Recommended Vaccines by Age

Vaccination is one of the best ways parents can protect infants, children, and teens from 16 potentially harmful diseases that can be very serious, may require hospitalization, or even be deadly.

And immunizations are not just for children. Protection from some childhood vaccines can wear off over time. Adults may also be at risk for vaccine-preventable disease due to age, job, lifestyle, travel, or health conditions.

Review the tabs below to learn what other vaccines you and your family may need. Check with your family’s healthcare professionals to make sure everyone is up to date on recommended vaccines.

Before leaving the hospital or birthing center, your baby receives the first of 3 doses of the vaccine that protects against Hepatitis B. Hepatitis B virus can cause chronic swelling of the liver and possible lifelong complications. It’s important to protect infants and young children from hepatitis B because they are more likely than adults to develop incurable chronic (long term) infection that can result in liver damage and liver cancer.

Recommended Immunization for for Kids fron Birth to 6 Years Old
Recommednded Chind & Adolescent Immunization Schedule

Recommended Adult Immunization Schedule
Immunization Schedule for Children Under 18Yrs & Younger

Immunization Schedule
Recommended Immunizations for Children from Birth through 6 years Old

Protect your baby by providing immunity early in life. Starting at 1 to 2 months of age, your baby receives the following vaccines to develop immunity from potentially harmful diseases:

  • Hepatitis B (2nd dose)

  • Diphtheria, tetanus, and whooping cough (pertussis) (DTaP)

  • Haemophilus influenzae type b (Hib)

  • Polio (IPV)

  • Pneumococcal (PCV)

  • Rotavirus (RV)

Immunization Schedule
Recommended Immunizations for Children from Birth through 6 years Old

Protect your baby by providing immunity early in life. Stay on track with the recommended vaccine schedule. At 4 months of age, your baby receives the following vaccines to develop immunity from potentially harmful diseases:

  • Diphtheria, tetanus, and whooping cough (pertussis) (DTaP)

  • Haemophilus influenzae type b (Hib)

  • Polio (IPV)

  • Pneumococcal (PCV)

  • Rotavirus (RV)

  • Hepatitis B (HepB)

Immunization Schedule
Recommended Immunizations for Children from Birth through 6 years Old

Protect your baby by providing immunity early in life. Stay on track with the recommended vaccine schedule. At 6 months of age, your baby receives the following vaccines to develop immunity from potentially harmful diseases:

  • Diphtheria, tetanus, and whooping cough (pertussis) (DTaP)

  • Haemophilus influenzae type b (Hib)

  • Polio (IPV)

  • Pneumococcal (PCV)

  • Rotavirus (RV)

  • Influenza (flu)

Immunization Schedule
Recommended Immunizations for Children from Birth through 6 years Old

There are usually no vaccinations scheduled between 7 and 11 months of age. However, if your baby has missed an earlier vaccination, now is a good time to “catch up.”

Babies 6 months and older should receive flu vaccination every flu season.

Immunization Schedule
Recommended Immunizations for Children from Birth through 6 years Ood.

By following the recommended schedule and fully immunizing your child by 2 years of age, your child should be protected against 14 vaccine preventable diseases. Between 12 and 23 months of age, your child receives the following vaccines to continue developing immunity from potentially harmful diseases:

  • Chickenpox (Varicella)

  • Diphtheria, tetanus, and whooping cough (pertussis) (DTaP)

  • Haemophilus influenzae type b (Hib)

  • Measles, mumps, rubella (MMR)

  • Polio (IPV) (between 6 through 18 months)

  • Pneumococcal (PCV)

  • Hepatitis A (HepA)

  • Hepatitis B (HepB)

Additionally, children should receive flu vaccination every flu season.

Immunization Schedule
Recommended Immunizations for Children from Birth through 6 years Old

Between 2 and 3 years of age, your child should visit the doctor once a year for check-ups.

Additionally, children should receive flu vaccination every flu season.

Immunization Schedule
Recommended Immunizations for Children from Birth through 6 years Old

Between 4 through 6 years of age, your child should visit the doctor once a year for check-ups. During this time, your child receives the following vaccines:

  • Diphtheria, tetanus and whooping cough (pertussis) (DTaP)

  • Polio (IPV)

  • Measles, mumps and rubella (MMR)

  • Chickenpox (varicella)

  • Influenza (flu) every year

Immunization Schedule
Recommended Immunizations for Children from Birth through 6 years Old

Between 7 and 10 years of age, your child should visit the doctor once a year for check-ups.

Additionally, children should receive flu vaccination every flu season.

Immunization Schedule
Recommended Immunizations for Preteens and Teens (7-18 years)

There are four vaccines recommended for preteens—these vaccines help protect your children, their friends, and their family members.

  • Meningococcal conjugate vaccine

  • HPV vaccine

  • Tdap

  • Flu vaccine every flu season

Immunization Schedule
Recommended Immunizations for Preteens and Teens (7-18 years)

Between 13 through 18 years old, your child should visit the doctor once each year for check-ups. This can be a great time to get any vaccines your teen may have missed or may need if traveling outside the United States.

Additional, everyone 6 months and older should receive flu vaccination every flu season.

Immunization Schedule
Recommended Immunizations for Preteens and Teens (7-18 years)

In addition to seasonal flu (influenza) vaccine and Td or Tdap vaccine (tetanus, diphtheria, and pertussis), you should also get HPV vaccine, which protects against the human papillomaviruses that cause most cervical, anal, and other cancers, as well as genital warts, if you were not vaccinated at a younger age (HPV vaccination is routinely recommended at age 11 or 12 years). HPV vaccination is also recommended for adults through age 26 years.

Some vaccines may be recommended for adults because of particular job or school-related requirements, health conditions, lifestyle or other factors. Some states require students entering colleges and universities to be vaccinated against certain diseases like meningitis due to increased risk among college students living in residential housing.

Immunization Schedules

Every adult should get the Tdap vaccine once if they did not receive it as an adolescent to protect against pertussis (whooping cough), and then a Td (tetanus, diphtheria) booster shot every 10 years. In addition, women should get the Tdap vaccine each time they are pregnant, preferably at 27 through 36 weeks.

Healthy adults aged 50 years and older should get a zoster vaccine to prevent shingles and the complications from the disease.

Some vaccines may be recommended for adults because of particular job or school-related requirements, health conditions, lifestyle or other factors.

Immunization Schedules

In addition to seasonal flu (influenza) vaccine and Td or Tdap vaccine (tetanus, diphtheria, and pertussis), people 65 years and older should also get:

  • Pneumococcal vaccines, which protect against pneumococcal disease, including infections in the lungs and bloodstream (recommended for all adults over 65 years old, and for adults younger than 65 years who have certain chronic health conditions)

  • Zoster vaccine, which protects against shingles (recommended for adults 50 years or older)

Immunization Schedules

Traditional vaccines contain either parts of microbes or whole microbes that have been killed or weakened so that they don’t cause disease. When your immune system confronts these harmless versions of the germs, it quickly clears them from your body.

Recommended Immunization for for Kids fron Birth to 6 Years Old
Recommednded Chind & Adolescent Immunization Schedule

Recommended Adult Immunization Schedule
Immunization Schedule for Children Under 18Yrs & Younger

Related Link: Vaccines & Immunization

Vaccines and Immunization

What Is a Vaccine?

Chances are you never had diphtheria. You probably don’t know anyone who has suffered from this disease, either. In fact, you may not know what diphtheria is. Similarly, diseases like whooping cough (pertussis), measles, mumps, and German measles (rubella) may be unfamiliar to you. In the 19th and early 20th centuries, these illnesses struck hundreds of thousands of people in the United States each year, mostly children, and tens of thousands of people died. The names of these diseases were frightening household words. Today, they are all but forgotten. That change happened largely because of vaccines.

Chances are you’ve been vaccinated against diphtheria. You may even have been exposed to the bacterium that causes it, but the vaccine prepared your body to fight off the disease so quickly that you were unaware of the infection. Vaccines take advantage of your body’s natural ability to learn how to combat many disease-causing germs, or microbes, that attack it. What’s more, your body “remembers” how to protect itself from the microbes it has encountered before. Collectively, the parts of your body that remember and repel microbes are called the immune system. Without the immune system, the simplest illness—even the common cold—could quickly turn deadly.

On average, your immune system takes more than a week to learn how to fight off an unfamiliar microbe. Sometimes that isn’t soon enough. Stronger microbes can spread through your body faster than the immune system can fend them off. Your body often gains the upper hand after a few weeks, but in the meantime you are sick. Certain microbes are so powerful, or virulent, that they can overwhelm or escape your body’s natural defenses. In those situations, vaccines can make all the difference.

Traditional vaccines contain either parts of microbes or whole microbes that have been killed or weakened so that they don’t cause disease. When your immune system confronts these harmless versions of the germs, it quickly clears them from your body. In other words, vaccines trick your immune system to teach your body important lessons about how to defeat its opponents.

Vaccine Benefits

Once your immune system is trained to resist a disease, you are said to be immune to it. Before vaccines, the only way to become immune to a disease was to actually get it and, with luck, survive it. This is called naturally acquired immunity. With naturally acquired immunity, you suffer the symptoms of the disease and also risk the complications, which can be quite serious or even deadly. In addition, during certain stages of the illness, you may be contagious and pass the disease to family members, friends, or others who come into contact with you.

The Impact of Vaccines in the United States


Baseline 20th Century Pre-Vaccine Annual Cases

2009 Cases

Percent Decrease

























Haemophilus influenzae type b, invasive












Widespread use of vaccines in the United States has eliminated or almost eliminated infectious diseases that were once terrifying household names. *Single case of oral vaccine-associated polio in 2009. Credit: Morbidity and Mortality Weekly Report, Centers for Disease Control and Prevention, 4/2/99, 11/12/10

Vaccines, which provide artificially acquired immunity, are an easier and less risky way to become immune. Vaccines can prevent a disease from occurring in the first place, rather than attempt to cure it after the fact.

Benefits for You and Others

It is also much cheaper to prevent a disease than to treat it. In a 2005 study on the economic impact of routine childhood immunization in the United States, researchers estimated that for every dollar spent, the vaccination program saved more than $5 in direct costs and approximately $11 in additional costs to society.

Vaccines protect not only yourself but also others around you. If your vaccine-primed immune system stops an illness before it starts, you will be contagious for a much shorter period of time, or perhaps not at all. Similarly, when other people are vaccinated, they are less likely to give the disease to you. Vaccines protect not only individuals but entire communities. That is why vaccines are vital to the public health goal of preventing diseases.

If a critical number of people within a community are vaccinated against a particular illness, the entire group becomes less likely to get the disease. This protection is called community, or herd, immunity. On the other hand, if too many people in a community do not get vaccinations, diseases can reappear. In 1989, low vaccination rates allowed a measles outbreak to occur in the United States. The outbreak resulted in more than 55,000 cases of measles and 136 measles-associated deaths.

How Vaccines Work

The human immune system is a complex network of cells and organs that evolved to fight off infectious microbes. Much of the immune system’s work is carried out by an army of various specialized cells, each type designed to fight disease in a particular way. The invading microbes first run into the vanguard of this army, which includes white blood cells called macrophages (literally, “big eaters”). The macrophages engulf as many of the microbes as they can.

Antigens Sound the Alarm

How do the macrophages recognize the microbes? All cells and microbes wear a “uniform” made up of molecules that cover their surfaces. Each human cell displays unique marker molecules unique to you. Microbes display different marker molecules unique to them. The macrophages and other cells of your immune system use these markers to distinguish among the cells that are part of your body, harmless bacteria that reside in your body, and harmful invading microbes that need to be destroyed.

The molecules on a microbe that identify it as foreign and stimulate the immune system to attack it are called “antigens.” Every microbe carries its own unique set of antigens, which are central to creating vaccines.

Macrophages digest most parts of the microbes but save the antigens and carry them back to the lymph nodes, bean-sized organs scattered throughout your body where immune system cells congregate. In these nodes, macrophages sound the alarm by “regurgitating” the antigens, displaying them on their surfaces so other cells, such as specialized defensive white blood cells called lymphocytes, can recognize them.

Lymphocytes Take Over

There are two major kinds of lymphocytes, T cells and B cells, and they do their own jobs in fighting off infection. T cells function either offensively or defensively. The offensive T cells don’t attack the microbe directly, but they use chemical weapons to eliminate the human cells that have already been infected. Because they have been “programmed” by their exposure to the microbe’s antigen, these cytotoxic T cells, also called killer T cells, can “sense” diseased cells that are harboring the microbe. The killer T cells latch onto these cells and release chemicals that destroy the infected cells and the microbes inside.

The defensive T cells, also called helper T cells, defend the body by secreting chemical signals that direct the activity of other immune system cells. Helper T cells assist in activating killer T cells, and helper T cells also stimulate and work closely with B cells. The work done by T cells is called the cellular or cell-mediated immune response.

B cells make and secrete extremely important molecular weapons called antibodies. Antibodies usually work by first grabbing onto the microbe’s antigen, and then sticking to and coating the microbe. Antibodies and antigens fit together like pieces of a jigsaw puzzle—if their shapes are compatible, they bind to each other.

Each antibody can usually fit with only one antigen. The immune system keeps a supply of millions and possibly billions of different antibodies on hand to be prepared for any foreign invader. It does this by constantly creating millions of new B cells. About 50 million B cells circulate in each teaspoonful of human blood, and almost every B cell—through random genetic shuffling—produces a unique antibody that it displays on its surface.

When these B cells come into contact with their matching microbial antigen, they are stimulated to divide into many larger cells, called plasma cells, which secrete mass quantities of antibodies to bind to the microbe.

Antibodies in Action

The antibodies secreted by B cells circulate throughout the human body and attack the microbes that have not yet infected any cells but are lurking in the blood or the spaces between cells. When antibodies gather on the surface of a microbe, it becomes unable to function. Antibodies signal macrophages and other defensive cells to come eat the microbe. Antibodies also work with other defensive molecules that circulate in the blood, called complement proteins, to destroy microbes.

The work of B cells is called the humoral immune response, or simply the antibody response. The goal of most vaccines is to stimulate this response. In fact, many infectious microbes can be defeated by antibodies alone, without any help from killer T cells.

Clearing the Infection: Memory Cells and Natural Immunity

When T cells and antibodies begin to eliminate the microbe faster than it can reproduce, the immune system finally has the upper hand. Gradually, the virus disappears from the body.

After the body eliminates the disease, some microbe-fighting B cells and T cells are converted into memory cells. Memory B cells can quickly divide into plasma cells and make more antibody if needed. Memory T cells can divide and grow into a microbe-fighting army. If re-exposure to the infectious microbe occurs, the immune system will quickly recognize how to stop the infection.

How Vaccines Mimic Infection

Vaccines teach the immune system by mimicking a natural infection. For example, the yellow fever vaccine, first widely used in 1938, contains a weakened form of the virus that doesn’t cause disease or reproduce very well. Human macrophages can’t tell that the vaccine viruses are weakened, so they engulf the viruses as if they were dangerous. In the lymph nodes, the macrophages present yellow fever antigen to T cells and B cells.

A response from yellow-fever-specific T cells is activated. B cells secrete yellow fever antibodies. The weakened viruses in the vaccine are quicky eliminated. The mock infection is cleared, and humans are left with a supply of memory T and B cells for future protection against yellow fever.


An adjuvant is a substance that is formulated as part of a vaccine to enhance its ability to induce protection against infection. Adjuvants help activate the immune system, allowing the antigens— pathogen components that elicit an immune response—in vaccines to stimulate a response that leads to long-term protection.

An effective vaccine stimulates both arms of the immune system: innate immunity and adaptive immunity. Innate immunity occurs within hours, as immune cells recognize an intruder. Adaptive immunity develops over several days and involves coordination and expansion of specific adaptive immune cells. This leads to immune memory, when cells specific to the pathogen are retained for later use. Vaccines made from weakened or killed pathogens contain naturally occurring adjuvants and can elicit potent protective immune responses. However, most vaccines developed today include small components of microbes, such as proteins, rather than the entire virus or bacterium. These vaccines often must be formulated with adjuvants to generate a strong, long-lasting protective immune response.

Vaccines to prevent infectious diseases have saved millions of lives worldwide, yet there remains a need for new and improved vaccines against existing and emerging infections. Efforts to develop safe and effective preventative vaccines increasingly involve the use of adjuvants—substances formulated as part of a vaccine to enhance its ability to induce protection against infection. Adjuvant discovery and development play critical roles in NIAID’s vaccine development efforts.

Types of Vaccines

Scientists take many approaches to designing vaccines against a microbe. These choices are typically based on fundamental information about the microbe, such as how it infects cells and how the immune system responds to it, as well as practical considerations, such as regions of the world where the vaccine would be used. The following are some of the options that researchers might pursue:

  • Live, attenuated vaccines

  • Inactivated vaccines

  • Subunit vaccines

  • Toxoid vaccines

  • Conjugate vaccines

  • DNA vaccines

  • Recombinant vector vaccines

Live, Attenuated Vaccines

Live, attenuated vaccines contain a version of the living microbe that has been weakened in the lab so it can’t cause disease. Because a live, attenuated vaccine is the closest thing to a natural infection, these vaccines are good “teachers” of the immune system: They elicit strong cellular and antibody responses and often confer lifelong immunity with only one or two doses.

Despite the advantages of live, attenuated vaccines, there are some downsides. It is the nature of living things to change, or mutate, and the organisms used in live, attenuated vaccines are no different. The remote possibility exists that an attenuated microbe in the vaccine could revert to a virulent form and cause disease. Also, not everyone can safely receive live, attenuated vaccines. For their own protection, people who have damaged or weakened immune systems—because they’ve undergone chemotherapy or have HIV, for example—cannot be given live vaccines.

Another limitation is that live, attenuated vaccines usually need to be refrigerated to stay potent. If the vaccine needs to be shipped overseas and stored by healthcare workers in developing countries that lack widespread refrigeration, a live vaccine may not be the best choice.

Live, attenuated vaccines are relatively easy to create for certain viruses. Vaccines against measles, mumps, and chickenpox, for example, are made by this method. Viruses are simple microbes containing a small number of genes, and scientists can therefore more readily control their characteristics. Viruses often are attenuated through a method of growing generations of them in cells in which they do not reproduce very well. This hostile environment takes the fight out of viruses: As they evolve to adapt to the new environment, they become weaker with respect to their natural host, human beings.

Live, attenuated vaccines are more difficult to create for bacteria. Bacteria have thousands of genes and thus are much harder to control. Scientists working on a live vaccine for a bacterium, however, might be able to use recombinant DNA technology to remove several key genes. This approach has been used to create a vaccine against the bacterium that causes cholera, Vibrio cholerae, although the live cholera vaccine has not been licensed in the United States.

Inactivated Vaccines

Scientists produce inactivated vaccines by killing the disease-causing microbe with chemicals, heat, or radiation. Such vaccines are more stable and safer than live vaccines: The dead microbes can’t mutate back to their disease-causing state. Inactivated vaccines usually don’t require refrigeration, and they can be easily stored and transported in a freeze-dried form, which makes them accessible to people in developing countries.

Most inactivated vaccines, however, stimulate a weaker immune system response than do live vaccines. So it would likely take several additional doses, or booster shots, to maintain a person’s immunity. This could be a drawback in areas where people don’t have regular access to health care and can’t get booster shots on time.

Subunit Vaccines

Instead of the entire microbe, subunit vaccines include only the antigens that best stimulate the immune system. In some cases, these vaccines use epitopes—the very specific parts of the antigen that antibodies or T cells recognize and bind to. Because subunit vaccines contain only the essential antigens and not all the other molecules that make up the microbe, the chances of adverse reactions to the vaccine are lower.

Subunit vaccines can contain anywhere from 1 to 20 or more antigens. Of course, identifying which antigens best stimulate the immune system is a tricky, time-consuming process. Once scientists do that, however, they can make subunit vaccines in one of two ways:

  • They can grow the microbe in the laboratory and then use chemicals to break it apart and gather the important antigens.

  • They can manufacture the antigen molecules from the microbe using recombinant DNA technology. Vaccines produced this way are called “recombinant subunit vaccines.”

A recombinant subunit vaccine has been made for the hepatitis B virus. Scientists inserted hepatitis B genes that code for important antigens into common baker’s yeast. The yeast then produced the antigens, which the scientists collected and purified for use in the vaccine. Research is continuing on a recombinant subunit vaccine against hepatitis C virus.

Toxoid Vaccines

For bacteria that secrete toxins, or harmful chemicals, a toxoid vaccine might be the answer. These vaccines are used when a bacterial toxin is the main cause of illness. Scientists have found that they can inactivate toxins by treating them with formalin, a solution of formaldehyde and sterilized water. Such “detoxified” toxins, called toxoids, are safe for use in vaccines.

When the immune system receives a vaccine containing a harmless toxoid, it learns how to fight off the natural toxin. The immune system produces antibodies that lock onto and block the toxin. Vaccines against diphtheria and tetanus are examples of toxoid vaccines.

Conjugate Vaccines

If a bacterium possesses an outer coating of sugar molecules called polysaccharides, as many harmful bacteria do, researchers may try making a conjugate vaccine for it. Polysaccharide coatings disguise a bacterium’s antigens so that the immature immune systems of infants and younger children can’t recognize or respond to them. Conjugate vaccines, a special type of subunit vaccine, get around this problem.

When making a conjugate vaccine, scientists link antigens or toxoids from a microbe that an infant’s immune system can recognize to the polysaccharides. The linkage helps the immature immune system react to polysaccharide coatings and defend against the disease-causing bacterium.

The vaccine that protects against Haemophilus influenzae type B (Hib) is a conjugate vaccine.

DNA Vaccines

The Making of a DNA Vaccine Against West Nile Virus.
Credit: NIAID

Once the genes from a microbe have been analyzed, scientists could attempt to create a DNA vaccine against it.

Still in the experimental stages, these vaccines show great promise, and several types are being tested in humans. DNA vaccines take immunization to a new technological level. These vaccines dispense with both the whole organism and its parts and get right down to the essentials: the microbe’s genetic material. In particular, DNA vaccines use the genes that code for those all-important antigens.

Researchers have found that when the genes for a microbe’s antigens are introduced into the body, some cells will take up that DNA. The DNA then instructs those cells to make the antigen molecules. The cells secrete the antigens and display them on their surfaces. In other words, the body’s own cells become vaccine-making factories, creating the antigens necessary to stimulate the immune system.

A DNA vaccine against a microbe would evoke a strong antibody response to the free-floating antigen secreted by cells, and the vaccine also would stimulate a strong cellular response against the microbial antigens displayed on cell surfaces. The DNA vaccine couldn’t cause the disease because it wouldn’t contain the microbe, just copies of a few of its genes. In addition, DNA vaccines are relatively easy and inexpensive to design and produce.

So-called naked DNA vaccines consist of DNA that is administered directly into the body. These vaccines can be administered with a needle and syringe or with a needle-less device that uses high-pressure gas to shoot microscopic gold particles coated with DNA directly into cells. Sometimes, the DNA is mixed with molecules that facilitate its uptake by the body’s cells. Naked DNA vaccines being tested in humans include those against the viruses that cause influenza and herpes.

Recombinant Vector Vaccines

Recombinant vector vaccines are experimental vaccines similar to DNA vaccines, but they use an attenuated virus or bacterium to introduce microbial DNA to cells of the body. “Vector” refers to the virus or bacterium used as the carrier.

In nature, viruses latch on to cells and inject their genetic material into them. In the lab, scientists have taken advantage of this process. They have figured out how to take the roomy genomes of certain harmless or attenuated viruses and insert portions of the genetic material from other microbes into them. The carrier viruses then ferry that microbial DNA to cells. Recombinant vector vaccines closely mimic a natural infection and therefore do a good job of stimulating the immune system.

Attenuated bacteria also can be used as vectors. In this case, the inserted genetic material causes the bacteria to display the antigens of other microbes on its surface. In effect, the harmless bacterium mimics a harmful microbe, provoking an immune response.

Researchers are working on both bacterial and viral-based recombinant vector vaccines for HIV, rabies, and measles.

Other Vaccine Ingredients

Vaccines may contain substances to maintain potency at less-than-optimal temperatures or to preserve sterility during production or after they are opened.

In addition to antigens and adjuvants, common vaccine components include the following:

  • Suspending fluid

  • Stabilizers

  • Preservatives

  • Trace components

A scientist holds a vial of freeze-dried vaccine. Credit: National Cancer Institute

Suspending fluid

Active vaccine components typically are suspended in sterile water, saline, or protein-containing liquids. Some vaccines are stored as freeze-dried powders and must be mixed with a liquid called a diluent before they can be administered. Diluents are specifically designed for each vaccine to ensure proper safety and potency.


Stabilizers are additives that protect vaccines from adverse conditions like high temperatures. Commonly used stabilizers include the sugars sucrose and lactose, the amino acid glycine, and monosodium glutamate, an amino acid salt. Proteins such as human or bovine serum albumin and gelatin also are used as stabilizers.


Preservatives such as phenol, phenoxyethanol, and thimerosal may be included in vaccines to prevent bacterial or fungal contamination. Phenol is a disinfectant and antiseptic. Phenoxyethanol is chemically related to phenol and also is used as a preservative in many cosmetics. Thimerosal is a mercury-containing compound that has been used as a preservative in some vaccines since the 1930s.

One product of the metabolism, or degradation within the body, of thimerosal is ethyl mercury, an organic derivative of mercury. A related compound found in many fish and shellfish, called methyl mercury, can be toxic to people at high levels (see a mercury exposure comparison chart). Due to concerns about mercury exposure, thimerosal was removed from most childhood vaccines by 2001 as a precautionary measure. Subsequent studies have shown that, unlike methyl mercury, ethyl mercury is quickly eliminated from the body and does not build up to toxic levels.

Trace components

A scientist checks chick embryo development before inoculating eggs with influenza virus suspension. Credit: Centers for Disease Control and Prevention

Some vaccines may contain residual quantities of components used during the manufacturing process, including inactivating agents, antibiotics, and cellular residuals. These agents are removed at the end of the manufacturing process, but trace amounts may be present in some vaccines.

Inactivating agents are used to eliminate the harmful effects of bacterial toxins or to render viruses incapable of causing disease. Examples of inactivating agents include formaldehyde and β-propiolactone. Formaldehyde is a naturally occurring chemical found in plants, animals, and the human body, where it plays a role in the synthesis of DNA and amino acids (the building blocks of proteins). Although prolonged exposure to high levels of formaldehyde can be harmful, the amount of the chemical present in certain vaccines is much lower than the amount naturally present in the body. Exposure to β-propiolactone also has been linked to health concerns. However, the chemical breaks down quickly in water-based solutions, and the very small amount of residual β-propiolactone in some vaccines is completely broken down and harmless.

Antibiotics sometimes are added to vaccines to ensure that bacterial contamination does not occur during the manufacturing process. Antibiotics used for this purpose include neomycin, streptomycin, polymyxin B, chlortetracyline, and amphotericin B. The antibiotics that are most likely to cause allergic reactions—penicillins, cephalosporins, and sulfonamides—are not used in vaccine manufacture.

Vaccine viruses can be produced in cells or cell culture, and trace amounts of cellular materials may be present in the final vaccine. The viruses incorporated into influenza and yellow fever vaccines, for example, are grown in chicken eggs, and the vaccines may contain traces of egg proteins. In general, people with egg allergy can receive these vaccines safely. In January 2013, the Food and Drug Administration approved the first egg-free flu vaccine, called Flublok. The antigens included in Flublok are produced in laboratory-grown insect cells.

Measles and mumps vaccine viruses are grown in chicken embryo tissue cultures. Studies have shown that the measles, mumps, and rubella (MMR) and measles, mumps, rubella, and varicella (MMRV) vaccines can be given safely to egg-allergic children, including those with severe allergy.

Other vaccine antigens, such as those used in hepatitis B vaccines and the human papillomavirus (HPV) vaccine Gardasil, are manufactured in yeast cells. These vaccines may contain small amounts of yeast proteins, which have not been shown to cause allergic reactions in people.

Vaccine Adjuvants

What Is a Vaccine Adjuvant?

An adjuvant is a substance that is formulated as part of a vaccine to enhance its ability to induce protection against infection. The word “adjuvant” comes from the Latin adjuvare and means “to help.” Adjuvants help activate the immune system, allowing the antigens—pathogen components that elicit an immune response—in vaccines to induce long-term protective immunity.

An effective vaccine stimulates both arms of the immune system: innate immunity and adaptive immunity. Innate immunity occurs within hours, as immune cells recognize a pathogen. Subsequently, the adaptive immune response develops over several days and involves coordination and expansion of adaptive immune cells called T and B cells. This leads to immune memory, when cells highly specific to the pathogen are retained for later use. Evidence suggests that adjuvants are important for activating the innate immune response, resulting in adaptive immunity with activation of T and B cells.

The first human vaccines were based on weakened or killed pathogens that cannot cause disease. These vaccines contain naturally occurring adjuvants and antigens and can elicit strong protective immune responses. Many of these types of vaccines are still widely used. For example, the seasonal flu shot contains killed influenza virus, and the nasal spray flu vaccine includes weakened virus.

The egg-free flu vaccine contains hemagglutinin (HA), the surface protein that binds influenza virus to the cell being infected, rather than killed influenza virus. HA antigen is produced using recombinant DNA technology. The HA gene is placed into baculovirus, a carrier virus that infects insect cells and is harmless to humans. Baculovirus-infected insect cells produce HA, which scientists harvest and purify from cell culture for inclusion in the vaccine. Credit: NIAID.

Most vaccines developed today include only the antigens that best stimulate the immune system, such as proteins, rather than the entire virus or microbe. For example, the egg-free flu vaccine contains an influenza virus protein that is produced in cell culture. Although this design makes vaccines safe and easier to produce, it often requires the incorporation of adjuvants to elicit a strong protective immune response.

Adjuvants Used in U.S. Vaccines

Alum, which is composed of aluminum salts, was the first vaccine adjuvant to be widely used in the United States. It has been used for more than 70 years. Alum is included in many U.S. vaccines, including those that prevent hepatitis B, human papillomavirus (HPV), and pneumococcus infections.

Alum was the only vaccine adjuvant in use in the United States until 2009, when the Food and Drug Administration approved Cervarix, an HPV vaccine that contains an adjuvant called AS04. This combination adjuvant is a mixture of alum and monophosphoryl lipid A (MPL), an immune-stimulating lipid (fat). Additional adjuvants have been licensed for use in other countries, and scientists continue to develop novel antigen-adjuvant combinations.

How Do Adjuvants Work?

A nurse administers a vaccine.

Credit: National Cancer Institute

Researchers have found that many vaccine adjuvants work by eliciting early or innate immune responses. Since the mid-1990s, scientists have made many new discoveries in the field of innate immunity. These advances have led to identification of many promising adjuvant candidates.

In some instances, scientists have identified the molecules on innate immune cells that adjuvants target, and these interactions can account for the adjuvant activity. However, the molecular mechanisms underlying the activity of many adjuvants are only partially understood. Researchers agree that adjuvants help direct particular types of immune responses, recruit specific populations of immune cells, and play a role in the ability of innate immune cells to shape the adaptive immune response (T and B cells). Adjuvants may function through a range of mechanisms. Increasing understanding of how adjuvants work to stimulate particular immune responses will play an important role in the development of new and improved vaccines.?

Benefits of Vaccine Adjuvants

Adjuvants have several important benefits, including the following:

Reducing the Amount of Antigen Required

Adding an adjuvant may reduce the amount of antigen, or pathogen component, required in a vaccine to elicit a protective immune response. The ability to increase the number of vaccine doses that can be produced for public use may be especially important during an epidemic or pandemic. For example, NIAID-supported scientists found that formulating an experimental H9N2 influenza vaccine with MF59 adjuvant greatly reduces the amount of antigen needed to elicit a strong protective response. Currently, MF59 is licensed for use as a vaccine adjuvant in Europe but not in the United States.

Reducing the Number of Vaccine Doses Needed

A person may need fewer doses of a vaccine containing a certain adjuvant because the immune response may be more effective. For example, results from clinical trials indicate that two doses of an investigational hepatitis B vaccine containing a novel adjuvant given over one month elicit potent, long-lasting protection. The current hepatitis B vaccine, which contains alum, requires three doses over six months. In addition, for a small number of people, the current vaccine does not confer immunity against the hepatitis B virus. Research suggests that the investigational vaccine is effective for almost everyone.

Enhancing Vaccine Effectiveness in Immunocompromised People

People with compromised immune systems, such as the elderly or the very young, may benefit from vaccines with adjuvants because their immune systems may require an extra boost to provide protection. For example, a European study showed that addition of MF59 adjuvant to a seasonal influenza vaccine boosted the vaccine’s effectiveness in young children from 43 percent to 89 percent.

Boosting the Immune-Stimulating Effects of Vaccines

Adjuvants are especially effective at boosting the immune-stimulating effects of newer vaccines, such as those made with purified antigens. By enhancing immune responses to pathogen antigens, adjuvants may help scientists develop vaccines against infectious diseases for which no effective vaccine currently exists, such as tuberculosis.

Offering Broad Protection

Adjuvanted vaccines may offer broad protection against related strains (types) of pathogens. For example, the human papillomavirus (HPV) vaccine Cervarix, which contains the AS04 adjuvant, is designed to prevent infection by HPV 16 and 18, the two strains that cause approximately 70 percent of cervical cancers. Results from clinical trials show that Cervarix protects against two additional cancer-causing strains, HPV 45 and 31.

Directing Specific Immune Responses

Adjuvants can direct specific immune responses to provide protection against the pathogen that the vaccine targets. Bacteria, viruses, and parasites use different infection strategies, and therefore, each is thwarted by different components of the immune system. Certain adjuvants may be more effective at stimulating responses to a particular vaccine antigen. Vaccine developers must tailor each antigen-adjuvant combination to maximize the safety and effectiveness of a vaccine. The availability of a toolbox of adjuvants would help scientists direct the different immune responses required against the many pathogens that cause disease. Therefore, to aid the development of new and improved vaccines, researchers are working to identify novel adjuvants and adjuvant-antigen combinations.

Like any medication, vaccines and adjuvants can cause side effects. The most common side effects of vaccines are mild and include redness or swelling at the injection site. However, in rare cases, vaccines may cause severe side effects such as allergic reactions. Identifying vaccine formulations that are safe as well as effective is a major focus of vaccine and adjuvant development research.

It is important to keep in mind, however, that the benefits of vaccines far outweigh the potential risks. Vaccines have greatly reduced the occurrence of many life-threatening diseases. For example, before the introduction of the measles vaccine, this disease affected over 500,000 people each year in the United States. According to the Centers for Disease Control and Prevention, an estimated 71 people were diagnosed with the disease in 2009, a 99.9 percent decrease from pre-vaccination levels.

Types of Vaccine Adjuvants

Only two adjuvants—alum and AS04—are used in commercially available vaccines in the United States, but others have been approved for use in Europe, and many others are being tested in clinical trials.

Some types of compounds being used or tested as adjuvants are highlighted below.

Pathogen Components

Naturally occurring parts of pathogens used as adjuvants can help trigger early non-specific, or innate, immune responses to vaccines. These adjuvants target various receptors inside or on the surface of innate immune cells. The innate immune system influences adaptive immune responses, which provide long-lasting protection against the pathogen that the vaccine targets. Examples of pathogen components tested and used as adjuvants include:

Poly(I:C) adjuvant comprises long strands of inosine and cytidine nucleotides. This image shows a single inosine-cytidine base pair. Credit: Wikimedia Commons

Monophosphoryl Lipid A

Monophosphoryl lipid A (MPL), an immune-stimulating lipid (fat), is combined with alum in the AS04 adjuvant used in the human papillomavirus vaccine Cervarix.


Poly(I:C) is synthetic double-stranded RNA, a molecular pattern associated with viral infection. In rhesus monkeys, poly(I:C)-containing vaccines against SIV—a close relative of HIV that causes an AIDS-like disease in monkeys—have elicited protective immune responses.

CpG DNA Adjuvants

CpG DNA adjuvants are short segments of DNA that include sequence motifs, or patterns, commonly found in bacterial DNA. Hepatitis B vaccines containing CpG-based adjuvants are being tested in clinical trials, and initial results suggest that the CpG-adjuvanted vaccines are safe and effective.


An emulsion is a blend of two liquids that are normally unmixable, such as water and oil. An oil-in-water emulsion called MF59 is used as an adjuvant in Fluad, an influenza vaccine available in Europe. MF59 helps recruit immune cells from the blood to the vaccine injection site.

Particulate Adjuvants

Particulate adjuvants form very small particles that can stimulate the immune system and also may enhance delivery of antigen to immune cells. Examples of particulate adjuvants include:


Alum, the most commonly used vaccine adjuvant, consists of aluminum salts that are not soluble in water. Alum is included in numerous vaccines, including those that prevent hepatitis B and human papillomavirus. Scientists are beginning to understand how alum stimulates vaccine-induced immunity. Gaining information about the mechanisms that alum uses to activate the immune system will help increase understanding of adjuvant function and facilitate the design of new vaccine adjuvants.


Virosomes, particles that resemble viruses but are noninfectious, are included as adjuvants in the flu vaccine Inflexal and the hepatitis A vaccine Epaxal, both licensed in Europe. The virosomes incorporated into these vaccines have antigens and other viral proteins on their surfaces, but they cannot cause infection because they do not contain any viral genetic material. Certain immune cells recognize these virus-like particles and engulf them. These cells then present the antigen to adaptive immune cells, which mount a protective response.


Cytokines are small proteins that serve as chemical messengers of the immune system. Because of their role in coordinating immune responses, some cytokines have been evaluated as vaccine adjuvants. For example, scientists have conducted animal studies to evaluate interleukin 12 (IL-12) as an adjuvant in vaccines against various bacterial and viral infections. Results from these studies suggest that IL-12 may increase protective immunity to some respiratory pathogens.

Combination Adjuvants

Combinations of adjuvants, such as AS04, also are of interest because of their ability to elicit multiple protective immune responses. Adjuvants that have a modest effect when used alone may induce a more potent immune response when used together.

Combination adjuvant research is in the early stages. Scientists must work to identify how adjuvants can be combined to elicit immune responses that are useful for a given antigen. A long-range goal of this line of research is to develop a toolbox of adjuvants that can be combined in different ways to elicit a certain type of immune response.

Source: Centers for Disease Control and Prevention,  HHS

Common Infections and Childhood Conditions

Childhood Immunization

Also called: Shots 

Today, children in the United States routinely get vaccines that protect them from more than a dozen diseases such as measles, polio, and tetanus. Most of these diseases are now at their lowest levels in history, thanks to years of immunization. Children must get at least some vaccines before they may attend school.

Vaccines help make you immune to serious diseases without getting sick first. Without a vaccine, you must actually get a disease in order to become immune to the germ that causes it. Vaccines work best when they are given at certain ages. For example, children don't receive measles vaccine until they are at least one year old. If it is given earlier it might not work as well. The Centers for Disease Control and Prevention publishes a schedule for childhood vaccines.

Although some of the vaccines you receive as a child provide protection for many years, adults need immunizations too.

Infectious Diseases

Also called: Communicable diseases 

Infectious diseases kill more people worldwide than any other single cause. Infectious diseases are caused by germs. Germs are tiny living things that are found everywhere - in air, soil and water. You can get infected by touching, eating, drinking or breathing something that contains a germ. Germs can also spread through animal and insect bites, kissing and sexual contact. Vaccines, proper hand washing and medicines can help prevent infections.

There are four main kinds of germs:

  • Bacteria - one-celled germs that multiply quickly and may release chemicals which can make you sick

  • Viruses - capsules that contain genetic material, and use your own cells to multiply

  • Fungi - primitive plants, like mushrooms or mildew

  • Protozoa - one-celled animals that use other living things for food and a place to live

Bacterial Infections

Bacteria are living things that have only one cell. Under a microscope, they look like balls, rods, or spirals. They are so small that a line of 1,000 could fit across a pencil eraser. Most bacteria won't hurt you - less than 1 percent of the different types make people sick. Many are helpful. Some bacteria help to digest food, destroy disease-causing cells, and give the body needed vitamins. Bacteria are also used in making healthy foods like yogurt and cheese.

But infectious bacteria can make you ill. They reproduce quickly in your body. Many give off chemicals called toxins, which can damage tissue and make you sick. Examples of bacteria that cause infections include Streptococcus, Staphylococcus, and E. coli.

Antibiotics are the usual treatment. When you take antibiotics, follow the directions carefully. Each time you take antibiotics, you increase the chances that bacteria in your body will learn to resist them. Later, you could get or spread an infection that those antibiotics cannot cure.

Fungal Infections

Also called: Mycoses 

If you have ever had athlete's foot or a yeast infection, you can blame a fungus. A fungus is a primitive organism. Mushrooms, mold and mildew are examples. Fungi live in air, in soil, on plants and in water. Some live in the human body. Only about half of all types of fungi are harmful.

Some fungi reproduce through tiny spores in the air. You can inhale the spores or they can land on you. As a result, fungal infections often start in the lungs or on the skin. You are more likely to get a fungal infection if you have a weakened immune system or take antibiotics.

Fungi can be difficult to kill. For skin and nail infections, you can apply medicine directly to the infected area. Oral antifungal medicines are also available for serious infections.

Parasitic Diseases

Parasites are living things that use other living things - like your body - for food and a place to live. You can get them from contaminated food or water, a bug bite, or sexual contact. Some parasitic diseases are easily treated and some are not.

Parasites range in size from tiny, one-celled organisms called protozoa to worms that can be seen with the naked eye. Some parasitic diseases occur in the United States. Contaminated water supplies can lead to Giardia infections. Cats can transmit toxoplasmosis, which is dangerous for pregnant women. Others, like malaria, are common in other parts of the world.

If you are traveling, it's important to drink only water you know is safe. Prevention is especially important. There are no vaccines for parasitic diseases. Some medicines are available to treat parasitic infections.


Also called: Rubeola 

Measles is an infectious disease caused by a virus. It spreads easily from person to person. It causes a blotchy red rash. The rash often starts on the head and moves down the body. Other symptoms include

  • Fever

  • Cough

  • Runny nose

  • Conjunctivitis (pink eye)

  • Feeling achy and run down

  • Tiny white spots inside the mouth

Sometimes measles can lead to serious problems. There is no treatment for measles, but the measles-mumps-rubella (MMR) vaccine can prevent it.

"German measles", also known as rubella, is a completely different illness.


Mumps is an illness caused by the mumps virus. It starts with

  • Fever

  • Headache

  • Muscle aches

  • Tiredness

  • Loss of appetite

After that, the salivary glands under the ears or jaw become swollen and tender. The swelling can be on one or both sides of the face. Symptoms last 7 to 10 days. Serious complications are rare.

You can catch mumps by being with another person who has it. There is no treatment for mumps, but the measles-mumps-rubella (MMR) vaccine can prevent it.

Before the routine vaccination program in the United States, mumps was a common illness in infants, children and young adults. Now it is a rare disease in the U.S.


Also called: German measles, Three day measles 

Rubella is an infection caused by a virus. It is usually mild with fever and a rash. About half of the people who get rubella do not have symptoms. If you do get them, symptoms may include

  • A rash that starts on the face and spreads to the body

  • Mild fever

  • Aching joints, especially in young women

  • Swollen glands

Rubella is most dangerous for a pregnant woman's baby. It can cause miscarriage or birth defects.

Rubella spreads when an infected person coughs or sneezes. People without symptoms can still spread it. There is no treatment, but the measles-mumps-rubella (MMR) vaccine can prevent it.


Also called: Herpes zoster, Postherpetic neuralgia 

Shingles is a disease caused by the varicella-zoster virus - the same virus that causes chickenpox. After you have chickenpox, the virus stays in your body. It may not cause problems for many years. As you get older, the virus may reappear as shingles. Although it is most common in people over age 50, anyone who has had chickenpox is at risk.

You can't catch shingles from someone who has it. However, if you have a shingles rash, you can pass the virus to someone who has never had chickenpox. This would usually be a child, who could get chickenpox instead of shingles. The virus spreads through direct contact with the rash, and cannot spread through the air.

Early signs of shingles include burning or shooting pain and tingling or itching, usually on one side of the body or face. The pain can be mild to severe. Rashes or blisters appear anywhere from one to 14 days later. If shingles appears on your face, it may affect your vision or hearing. The pain of shingles may last for weeks, months, or even years after the blisters have healed.

There is no cure for shingles. Early treatment with medicines that fight the virus may help. These medicines may also help prevent lingering pain.

A vaccine may prevent shingles or lessen its effects. The vaccine is recommended for people 60 or over. In some cases doctors may give it to people ages 50 to 59.


Also called: Varicella 

Chickenpox is an infection caused by the varicella-zoster virus. Most cases are in children under age 15, but older children and adults can get it. It spreads very easily from one person to another.

The classic symptom of chickenpox is an uncomfortable, itchy rash. The rash turns into fluid-filled blisters and eventually into scabs. It usually shows up on the face, chest, and back and then spreads to the rest of the body. Other symptoms include

  • Fever

  • Headache

  • Tiredness

  • Loss of appetite

Chickenpox is usually mild and lasts 5 to 10 days. Calamine lotions and oatmeal baths can help with itching. Acetaminophen can treat the fever. Do not use aspirin for chickenpox; that combination can cause Reye syndrome.

Chickenpox can sometimes cause serious problems. Adults, babies, teenagers, pregnant women, and those with weak immune systems tend to get sicker from it. They may need to take antiviral medicines.

Once you catch chickenpox, the virus usually stays in your body. You probably will not get chickenpox again, but the virus can cause shingles in adults. A chickenpox vaccine can help prevent most cases of chickenpox, or make it less severe if you do get it.

Coronavirus Infections

Coronaviruses are common viruses that most people get some time in their life. They are common throughout the world, and they can infect people and animals. Several different coronaviruses can infect people and make them sick. They usually cause mild to moderate upper-respiratory illness. But, some coronaviruses can cause severe illness.

Coronaviruses probably spread through the air by coughing or sneezing, or by close personal contact. If you get infected, symptoms may include

  • Runny nose

  • Cough

  • Sore throat

  • Fever

You may be able to reduce your risk of infection by washing your hands often with soap and water, not touching your eyes, nose, or mouth, and avoiding close contact with people who are sick. There is no vaccine to prevent coronavirus infection. There are no specific treatments. You can relieve symptoms with pain and fever medicines and rest.


Also called: Bronchopneumonia  

Pneumonia is an infection in one or both of the lungs. Many germs, such as bacteria, viruses, and fungi, can cause pneumonia. You can also get pneumonia by inhaling a liquid or chemical. People most at risk are older than 65 or younger than 2 years of age, or already have health problems.

Symptoms of pneumonia vary from mild to severe. See your doctor promptly if you

  • Have a high fever

  • Have shaking chills

  • Have a cough with phlegm that doesn't improve or gets worse

  • Develop shortness of breath with normal daily activities

  • Have chest pain when you breathe or cough

  • Feel suddenly worse after a cold or the flu

Your doctor will use your medical history, a physical exam, and lab tests to diagnose pneumonia. Treatment depends on what kind you have. If bacteria are the cause, antibiotics should help. If you have viral pneumonia, your doctor may prescribe an antiviral medicine to treat it.

Preventing pneumonia is always better than treating it. Vaccines are available to prevent pneumococcal pneumonia and the flu. Other preventive measures include washing your hands frequently and not smoking.

Haemophilus Infections

Haemophilus is the name of a group of bacteria. There are several types of Haemophilus. They can cause different types of illnesses involving breathing, bones and joints, and the nervous system.

One common type, Hib (Haemophilus influenzae type b), causes serious disease. It usually strikes children under 5 years old. Your child can get Hib disease by being around other children or adults who may have the bacteria and not know it. The germs spread from person to person. If the germs stay in the child's nose and throat, the child probably will not get sick. But sometimes the germs spread into the lungs or the bloodstream, and then Hib can cause serious problems such as meningitis and pneumonia.

There is a vaccine to prevent Hib disease. All children younger than 5 years of age should be vaccinated with the Hib vaccine.


Also called: Spinal meningitis 

Meningitis is inflammation of the thin tissue that surrounds the brain and spinal cord, called the meninges. There are several types of meningitis. The most common is viral meningitis, which you get when a virus enters the body through the nose or mouth and travels to the brain. Bacterial meningitis is rare, but can be deadly. It usually starts with bacteria that cause a cold-like infection. It can block blood vessels in the brain and lead to stroke and brain damage. It can also harm other organs. Pneumococcal infections and meningococcal infections can cause bacterial meningitis.

Anyone can get meningitis, but it is more common in people whose bodies have trouble fighting infections. Meningitis can progress rapidly. You should seek medical care quickly if you have

  • A sudden fever

  • A severe headache

  • A stiff neck

Early treatment can help prevent serious problems, including death. Vaccines can prevent some of the bacterial infections that cause meningitis. Parents of adolescents and students living in college dorms should talk to a doctor about the vaccination.


 Encephalitis is an inflammation of the brain. Usually the cause is a viral infection, but bacteria can also cause it. It can be mild or severe. Most cases are mild. You may have flu-like symptoms. With a mild case, you may just need rest, plenty of fluids, and a pain reliever.

Severe cases need immediate treatment. Symptoms of severe cases include

  • Severe headache

  • Sudden fever

  • Drowsiness

  • Vomiting

  • Confusion

  • Seizures

In babies, additional symptoms may include constant crying, poor feeding, body stiffness, and bulging in the soft spots of the skull.

Severe cases may require a stay in the hospital. Treatments include oral and intravenous medicines to reduce inflammation and treat infection. Patients with breathing difficulties may need artificial respiration. Some people may need physical, speech, and occupational therapy once the illness is under control.

West Nile Virus

Also called: WNV 

West Nile virus (WNV) is an infectious disease that first appeared in the United States in 1999. Infected mosquitoes spread the virus that causes it. People who get WNV usually have no symptoms or mild symptoms. The symptoms include a fever, headache, body aches, skin rash, and swollen lymph glands. They can last a few days to several weeks, and usually go away on their own.

If West Nile virus enters the brain, however, it can be life-threatening. It may cause inflammation of the brain, called encephalitis, or inflammation of the tissue that surrounds the brain and spinal cord, called meningitis. A physical exam, health history and laboratory tests can diagnose it.

Older people and those with weakened immune systems are most at risk. There are no specific vaccines or treatments for human WNV disease. The best way to avoid WNV is to prevent mosquito bites:

  • Use insect repellent

  • Get rid of mosquito breeding sites by emptying standing water from flower pots, buckets or barrels

  • Stay indoors between dusk and dawn, when mosquitoes are most active

  • Use screens on windows to keep mosquitoes out

Insect Bites and Stings

Also called: Bug bites  

Most insect bites are harmless, though they sometimes cause discomfort. Bee, wasp, and hornet stings and fire ant bites usually hurt. Mosquito, flea, and mite bites usually itch. Insects can also spread diseases. In the United States, some mosquitoes spread West Nile virus. Travelers outside the United States may be at risk for malaria and other infections.

To prevent insect bites and their complications

  • Don't bother insects

  • Use insect repellant

  • Wear protective clothing

  • Be careful when you eat outside because food attracts insects

  • If you know you have severe allergic reactions to insect bites, carry an emergency epinephrine kit


Also called: Bubonic plague, Pneumonic plague 

Plague is an infection caused by the bacterium Yersinia pestis. The bacteria are found mainly in rats and in the fleas that feed on them. People and other animals can get plague from rat or flea bites. In the past, plague destroyed entire civilizations. Today plague is uncommon, due to better living conditions and antibiotics.

There are three forms of plague:

  • Bubonic plague causes the tonsils, adenoids, spleen, and thymus to become inflamed. Symptoms include fever, aches, chills, and tender lymph glands.

  • In septicemic plague, bacteria multiply in the blood. It causes fever, chills, shock, and bleeding under the skin or other organs.

  • Pneumonic plague is the most serious form. Bacteria enter the lungs and cause pneumonia. People with the infection can spread this form to others. This type could be a bioterror agent.

Lab tests can diagnose plague. Treatment is a strong antibiotic. There is no vaccine.

Biodefense and Bioterrorism

A bioterrorism attack is the deliberate release of viruses, bacteria, or other germs to cause illness or death. These germs are often found in nature. But they can sometimes be made more harmful by increasing their ability to cause disease, spread, or resist medical treatment.

Biological agents spread through the air, water, or in food. Some can also spread from person to person. They can be very hard to detect. They don't cause illness for several hours or days. Scientists worry that anthrax, botulism, Ebola and other hemorrhagic fever viruses, plague, or smallpox could be used as biological agents.

Biodefense uses medical measures to protect people against bioterrorism. This includes medicines and vaccinations. It also includes medical research and preparations to defend against bioterrorist attacks.


Also called: Vaccination 

Shots may hurt a little, but the diseases they can prevent are a lot worse. Some are even life-threatening. Immunization shots, or vaccinations, are essential. They protect against things like measles, mumps, rubella, hepatitis B, polio, diphtheria, tetanus, and pertussis (whooping cough). Immunizations are important for adults as well as children.

Your immune system helps your body fight germs by producing substances to combat them. Once it does, the immune system "remembers" the germ and can fight it again. Vaccines contain germs that have been killed or weakened. When given to a healthy person, the vaccine triggers the immune system to respond and thus build immunity.

Before vaccines, people became immune only by actually getting a disease and surviving it. Immunizations are an easier and less risky way to become immune.


Smallpox is a disease caused by the Variola major virus. Some experts say that over the centuries it has killed more people than all other infectious diseases combined. Worldwide immunization stopped the spread of smallpox three decades ago. The last case was reported in 1977. Two research labs still keep small amounts of the virus. Experts fear bioterrorists could use the virus to spread disease.

Smallpox spreads very easily from person to person. Symptoms are flu-like. They include

  • High fever

  • Fatigue

  • Headache

  • Backache

  • A rash with flat red sores

There is no treatment. Fluids and medicines for pain or fever can help control symptoms. Most people recover, but some can die. Those who do recover may have severe scars.

The U.S. stopped routine smallpox vaccinations in 1972. Military and other high-risk groups continue to get the vaccine. The U.S. has increased its supply of the vaccine in recent years. The vaccine makes some people sick, so doctors save it for those at highest risk of disease.


Antibiotics are powerful medicines that fight bacterial infections. Used properly, antibiotics can save lives. They either kill bacteria or keep them from reproducing. Your body's natural defenses can usually take it from there.

Antibiotics do not fight infections caused by viruses, such as

  • Colds

  • Flu

  • Most coughs and bronchitis

  • Sore throats, unless caused by strep

If a virus is making you sick, taking antibiotics may do more harm than good. Each time you take antibiotics, you increase the chances that bacteria in your body will be able to resist them. Later, you could get or spread an infection that those antibiotics cannot cure. Methicillin-resistant Staphylococcus aureus (MRSA) causes infections that are resistant to several common antibiotics.

When you take antibiotics, follow the directions carefully. It is important to finish your medicine even if you feel better. If you stop treatment too soon, some bacteria may survive and re-infect you. Do not save antibiotics for later or use someone else's prescription.


Also called: Methicillin-resistant Staphylococcus aureus 

MRSA stands for methicillin-resistant Staphylococcus aureus. It causes a staph infection (pronounced "staff infection") that is resistant to several common antibiotics. There are two types of infection. Hospital-associated MRSA happens to people in healthcare settings. Community-associated MRSA happens to people who have close skin-to-skin contact with others, such as athletes involved in football and wrestling.

Infection control is key to stopping MRSA in hospitals. To prevent community-associated MRSA

  • Practice good hygiene

  • Keep cuts and scrapes clean and covered with a bandage until healed

  • Avoid contact with other people's wounds or bandages

  • Avoid sharing personal items, such as towels, washcloths, razors, or clothes

  • Wash soiled sheets, towels, and clothes in hot water with bleach and dry in a hot dryer

If a wound appears to be infected, see a health care provider. Treatments may include draining the infection and antibiotics.

Staphylococcal Infections

Also called: Staph 

Staph is short for Staphylococcus, a type of bacteria. There are over 30 types, but Staphylococcus aureus causes most staph infections (pronounced "staff infections"), including

  • Skin infections

  • Pneumonia

  • Food poisoning

  • Toxic shock syndrome

  • Blood poisoning (bacteremia)

Skin infections are the most common. They can look like pimples or boils. They may be red, swollen and painful, and sometimes have pus or other drainage. They can turn into impetigo, which turns into a crust on the skin, or cellulitis, a swollen, red area of skin that feels hot.

Anyone can get a staph skin infection. You are more likely to get one if you have a cut or scratch, or have contact with a person or surface that has staph bacteria. The best way to prevent staph is to keep hands and wounds clean. Most staph skin infections are easily treated with antibiotics or by draining the infection. Some staph bacteria such as MRSA (methicillin-resistant Staphylococcus aureus) are resistant to certain antibiotics, making infections harder to treat.

Infection Control

Every year, lives are lost because of the spread of infections in hospitals. Health care workers can take steps to prevent the spread of infectious diseases. These steps are part of infection control.

Proper hand washing is the most effective way to prevent the spread of infections in hospitals. If you are a patient, don't be afraid to remind friends, family and health care providers to wash their hands before getting close to you.

Other steps health care workers can take include

  • Covering coughs and sneezes

  • Staying up-to-date with immunizations

  • Using gloves, masks and protective clothing

  • Making tissues and hand cleaners available

  • Following hospital guidelines when dealing with blood or contaminated items


Cellulitis is an infection of the skin and deep underlying tissues. Group A strep (streptococcal) bacteria are the most common cause. The bacteria enter your body when you get an injury such as a bruise, burn, surgical cut, or wound.

Symptoms include

  • Fever and chills

  • Swollen glands or lymph nodes

  • A rash with painful, red, tender skin. The skin may blister and scab over.

Your health care provider may take a sample or culture from your skin or do a blood test to identify the bacteria causing infection. Treatment is with antibiotics. They may be oral in mild cases, or intravenous (through the vein) for more severe cases.


Impetigo is a skin infection caused by bacteria. It is usually caused by staphylococcal (staph) bacteria, but it can also be caused by streptococcal (strep) bacteria. It is most common in children between the ages of two and six. It usually starts when bacteria get into a break in the skin, such as a cut, scratch, or insect bite.

Symptoms start with red or pimple-like sores surrounded by red skin. These sores can be anywhere, but usually they occur on your face, arms and legs. The sores fill with pus, then break open after a few days and form a thick crust. They are often itchy, but scratching them can spread the sores.

Impetigo can spread by contact with sores or nasal discharge from an infected person. You can treat impetigo with antibiotics.


Also called: Viral hepatitis 

Your liver is the largest organ inside your body. It helps your body digest food, store energy, and remove poisons. Hepatitis is an inflammation of the liver.

Viruses cause most cases of hepatitis. The type of hepatitis is named for the virus that causes it; for example, hepatitis A, hepatitis B or hepatitis C. Drug or alcohol use can also cause hepatitis. In other cases, your body mistakenly attacks healthy cells in the liver.

Some people who have hepatitis have no symptoms. Others may have

  • Loss of appetite

  • Nausea and vomiting

  • Diarrhea

  • Dark-colored urine and pale bowel movements

  • Stomach pain

  • Jaundice, yellowing of skin and eyes

Some forms of hepatitis are mild, and others can be serious. Some can lead to scarring, called cirrhosis, or to liver cancer.

Sometimes hepatitis goes away by itself. If it does not, it can be treated with drugs. Sometimes hepatitis lasts a lifetime. Vaccines can help prevent some viral forms.


Also called: Acquired immunodeficiency syndrome, AIDS, HIV, Human immunodeficiency virus 

HIV stands for human immunodeficiency virus. It kills or damages the body's immune system cells. AIDS stands for acquired immunodeficiency syndrome. It is the most advanced stage of infection with HIV.

HIV most often spreads through unprotected sex with an infected person. It may also spread by sharing drug needles or through contact with the blood of an infected person. Women can give it to their babies during pregnancy or childbirth.

The first signs of HIV infection may be swollen glands and flu-like symptoms. These may come and go a month or two after infection. Severe symptoms may not appear until months or years later.

A blood test can tell if you have HIV infection. Your health care provider can perform the test, or call the national referral hotline at 1-800-CDC-INFO (24 hours a day, 1-800-232-4636 in English and en español; 1-888-232-6348 - TTY).

There is no cure, but there are many medicines to fight both HIV infection and the infections and cancers that come with it. People can live with the disease for many years.

Meningococcal Infections

Meningococci are a type of bacteria that cause serious infections. The most common infection is meningitis, which is an inflammation of the thin tissue that surrounds the brain and spinal cord. Meningococci can also cause other problems, including a serious bloodstream infection called sepsis.

Meningococcal infections can spread from person to person. Risk factors include

  • Age - it is more common in infants, teens, and young adults

  • Living in close quarters, such as in college dorms or military settings

  • Certain medical conditions, such as not having a spleen

  • Travel to areas where meningococcal disease is common

In its early stages, you may have flu-like symptoms and a stiff neck. But the disease can progress quickly and can be fatal. Early diagnosis and treatment are extremely important. Lab tests on your blood and cerebrospinal fluid can tell if you have it. Treatment is with antibiotics. Since the infection spreads from person to person, family members may also need to be treated.

Legionnaires' Disease

Also called: Legionellosis 

Legionnaires' disease is a type of pneumonia caused by bacteria. You usually get it by breathing in mist from water that contains the bacteria. The mist may come from hot tubs, showers, or air-conditioning units for large buildings. The bacteria don't spread from person to person.

Symptoms of Legionnaires' disease include high fever, chills, a cough, and sometimes muscle aches and headaches. Other types of pneumonia have similar symptoms. You will probably need a chest x-ray to diagnose the pneumonia. Lab tests can detect the specific bacteria that cause Legionnaires' disease.

Most people exposed to the bacteria do not become sick. You are more likely to get sick if you

  • Are older than 50

  • Smoke

  • Have a chronic lung disease

  • Have a weak immune system

Legionnaires' disease is serious and can be life-threatening. However, most people recover with antibiotic treatment.

Pneumocystis Infections

Pneumocystis jirovec is a tiny fungus that lives in the lungs of many people. Most people's immune systems keep the fungus under control. But if your immune system is weak, the fungus can make you very sick.

The most common problem of infection is pneumocystis pneumonia (PCP). PCP once was the major cause of death for people with HIV/AIDS. But now, it is possible to prevent or treat most cases. The key to surviving PCP is early treatment. The first signs of PCP are difficulty breathing, fever and a dry cough. If you have these symptoms, see your doctor right away.

Cytomegalovirus Infections

Also called: CMV 

Cytomegalovirus (CMV) is a virus found around the world. It is related to the viruses that cause chickenpox and infectious mononucleosis (mono). Between 50 percent and 80 percent of adults in the United States have had a CMV infection by age 40. Once CMV is in a person's body, it stays there for life.

CMV is spread through close contact with body fluids. Most people with CMV don't get sick and don't know that they've been infected. But infection with the virus can be serious in babies and people with weak immune systems. If a woman gets CMV when she is pregnant, she can pass it on to her baby. Usually the babies do not have health problems. But some babies can develop lifelong disabilities.

A blood test can tell whether a person has ever been infected with CMV. Most people with CMV don't need treatment. If you have a weakened immune system, your doctor may prescribe antiviral medicine. Good hygiene, including proper hand washing, may help prevent infections.


Also called: Break-bone fever, Dengue fever 

Dengue is an infection caused by a virus. You can get it if an infected mosquito bites you. Dengue does not spread from person to person. It is common in warm, wet areas of the world. Outbreaks occur in the rainy season. Dengue is rare in the United States.

Symptoms include a high fever, headaches, joint and muscle pain, vomiting, and a rash. In some cases, dengue turns into dengue hemorrhagic fever, which causes bleeding from your nose, gums, or under your skin. It can also become dengue shock syndrome, which causes massive bleeding and shock. These forms of dengue are life-threatening.

There is no specific treatment. Most people with dengue recover within 2 weeks. Until then, drinking lots of fluids, resting and taking non-aspirin fever-reducing medicines might help. People with the more severe forms of dengue usually need to go to the hospital and get fluids.

To lower your risk when traveling in dengue-prone countries

  • Wear insect repellent with DEET

  • Wear clothes that cover your arms, legs and feet

  • Close unscreened doors and windows


Also called: Ebola hemorrhagic fever, Ebola virus disease 

Ebola hemorrhagic fever is caused by a virus. It is a severe and often fatal disease. It can affect humans and other primates. Researchers believe that the virus first spreads from an infected animal to a human. It can then spread from human to human through direct contact with a patient's blood or secretions.

Symptoms of Ebola may appear anywhere from 2 to 21 days after exposure to the virus. Symptoms usually include

  • Fever

  • Headache

  • Joint and muscle aches

  • Weakness

  • Diarrhea

  • Vomiting

  • Stomach pain

  • Lack of appetite

Other symptoms including rash, red eyes, and internal and external bleeding, may also occur.

The early symptoms of Ebola are similar to other, more common, diseases. This makes it difficult to diagnose Ebola in someone who has been infected for only a few days. However, if a person has the early symptoms of Ebola and there is reason to suspect Ebola, the patient should be isolated. It is also important to notify public health professionals. Lab tests can confirm whether the patient has Ebola.

There is no cure for Ebola. Treatment involves supportive care such as fluids, oxygen, and treatment of complications. Some people who get Ebola are able to recover, but many do not.

Fifth Disease

Also called: Erythema infectiosum 

Fifth disease is a viral infection caused by parvovirus B19. The virus only infects humans; it's not the same parvovirus that dogs and cats can get. Fifth disease mostly affects children. Symptoms can include a low fever, cold symptoms, and a headache. Then you get a red rash on your face. It looks like a "slapped cheek." The rash can spread to the arms, legs, and trunk. Adults who get it might also have joint pain and swelling.

Fifth disease spreads easily, through saliva and mucus. You can get it when an infected person coughs or sneezes. Frequently washing your hands might help prevent getting the virus. Most people become immune to the virus after having it once.

Fifth disease is usually mild and goes away on its own. However, it can be serious if you

  • Are pregnant

  • Are anemic

  • Have cancer or a weak immune system

Hantavirus Infections

Also called: HPS 

Hantavirus pulmonary syndrome (HPS) is a rare but deadly viral infection. It is spread by mice and rats. They shed the virus in their urine, droppings, and saliva. Tiny droplets with the virus can enter the air. People can get the disease if they breathe infected air or come into contact with rodents or their urine or droppings. You cannot catch it from people.

Early symptoms of HPS include

  • Fatigue

  • Fever

  • Muscle aches, especially in the thighs, hips and back

  • Headaches

  • Chills

  • Dizziness

  • Nausea, vomiting, diarrhea or abdominal pain

Later symptoms include coughing and shortness of breath.

Controlling rodents in and around your house is the best way to prevent infection. If you have been around rodents and have symptoms of fever, deep muscle aches, and severe shortness of breath, see your doctor immediately.

There is no specific treatment, cure, or vaccine for HPS. Patients may do better if it is recognized early and they get medical care in an intensive care unit. They often need to use a breathing machine and have oxygen therapy.

Hemorrhagic Fevers

Also called: VHFs 

Viral hemorrhagic fevers (VHFs) are a group of illnesses caused by four families of viruses. These include the Ebola and Marburg, Lassa fever, and yellow fever viruses. VHFs have common features: they affect many organs, they damage the blood vessels, and they affect the body's ability to regulate itself. Some VHFs cause mild disease, but some, like Ebola or Marburg, cause severe disease and death.

VHFs are found around the world. Specific diseases are usually limited to areas where the animals that carry them live. For example, Lassa fever is limited to rural areas of West Africa where rats and mice carry the virus.

The risk for travelers is low, but you should avoid visiting areas where there are disease outbreaks. Because there are no effective treatments for some of these viral infections, there is concern about their use in bioterrorism.

Hepatitis C

Also called: HCV 

Your liver is the largest organ inside your body. It helps your body digest food, store energy, and remove poisons. Hepatitis is an inflammation of the liver. One type, hepatitis C, is caused by the hepatitis C virus (HCV). It usually spreads through contact with infected blood. It can also spread through sex with an infected person and from mother to baby during childbirth.

Most people who are infected with hepatitis C don't have any symptoms for years. If you do get symptoms, you may feel as if you have the flu. You may also have jaundice, a yellowing of skin and eyes, dark-colored urine, and pale bowel movements. A blood test can tell if you have it. Usually, hepatitis C does not get better by itself. The infection can last a lifetime and may lead to scarring of the liver or liver cancer. Medicines sometimes help, but side effects can be a problem. Serious cases may need a liver transplant.

There is no vaccine for HCV.

Herpes Simplex

Also called: HSV 

Herpes is an infection that is caused by a herpes simplex virus (HSV). Oral herpes causes cold sores around the mouth or face. Genital herpes affects the genitals, buttocks or anal area. Genital herpes is a sexually transmitted disease (STD). It affects the genitals, buttocks or anal area. Other herpes infections can affect the eyes, skin, or other parts of the body. The virus can be dangerous in newborn babies or in people with weak immune systems.

There are two types of HSV:

  • HSV type 1 most commonly causes cold sores. It can also cause genital herpes.

  • HSV type 2 is the usual cause of genital herpes, but it also can infect the mouth.

HSV spreads through direct contact. Some people have no symptoms. Others get sores near the area where the virus has entered the body. They turn into blisters, become itchy and painful, and then heal.

Most people have outbreaks several times a year. Over time, you get them less often. Medicines to help your body fight the virus can help lessen symptoms and decrease outbreaks.

Cold Sores

Also called: Fever blister, Oral herpes 

Cold sores are caused by a contagious virus called herpes simplex. There are two types of herpes simplex virus. Type 1 usually causes oral herpes, or cold sores. Type 1 herpes virus infects more than half of the U.S. population by the time they reach their 20s. Type 2 usually affects the genital area

Some people have no symptoms from the infection. But others develop painful and unsightly cold sores that last for a week or more. Cold sores usually occur outside the mouth -- on the lips, chin, and cheeks, or in the nostrils. When they do occur inside the mouth, it is usually on the gums or the roof of the mouth.

There is no cure for cold sores. Medicines can relieve some of the pain and discomfort associated with the sores. These include ointments that numb the blisters, antibiotics that control secondary bacterial infections, and ointments that soften the crusts of the sores.

Genital Herpes

Also called: Herpes genitalis 

Genital herpes is a sexually transmitted disease (STD) caused by a herpes simplex virus (HSV). It can cause sores on your genital or rectal area, buttocks, and thighs. You can get it from having sex, even oral sex. The virus can spread even when sores are not present. Mothers can also infect their babies during childbirth.

Symptoms of herpes are called outbreaks. You usually get sores near the area where the virus has entered the body. They turn into blisters, become itchy and painful, and then heal. Sometimes people do not know they have herpes because they have no symptoms or very mild symptoms. The virus can be more serious in newborn babies or in people with weak immune systems.

Most people have outbreaks several times a year. Over time, you get them less often and the symptoms become milder. The virus stays in your body for life.

Medicines do not cure genital herpes, but they can help your body fight the virus. This can help lessen symptoms, decrease outbreaks, and lower the risk of passing the virus to others. Correct usage of latex condoms can reduce, but not eliminate, the risk of catching or spreading herpes.


Also called: Human papillomavirus 

Human papillomaviruses (HPV) are common viruses that can cause warts. There are more than 100 types of HPV. Most are harmless, but about 30 types put you at risk for cancer. These types affect the genitals and you get them through sexual contact with an infected partner. They can be either low-risk or high-risk. Low-risk HPV can cause genital warts. High-risk HPV can lead to cancers of the cervix, vulva, vagina, and anus in women. In men, it can lead to cancers of the anus and penis.

Although some people develop genital warts from HPV infection, others have no symptoms. Your health care provider can treat or remove the warts. In women, Pap tests can detect changes in the cervix that might lead to cancer. Both Pap and HPV tests are types of cervical cancer screening.

Correct usage of latex condoms greatly reduces, but does not eliminate, the risk of catching or spreading HPV. Vaccines can protect against several types of HPV, including some that can cause cancer.

Infectious Mononucleosis

Also called: Glandular fever, Kissing disease, Mono, Mononucleosis 

Infectious mononucleosis, or "mono", is an infection usually caused by the Epstein-Barr virus. The virus spreads through saliva, which is why it's sometimes called "kissing disease." Mono occurs most often in teens and young adults. However, you can get it at any age. Symptoms of mono include

  • Fever

  • Sore throat

  • Swollen lymph glands

Sometimes you may also have a swollen spleen. Serious problems are rare.

A blood test can show if you have mono. Most people get better in two to four weeks. However, you may feel tired for a few months afterward. Treatment focuses on helping symptoms and includes medicines for pain and fever, warm salt water gargles and plenty of rest and fluids.

Monkeypox Virus Infections

Monkeypox is a rare viral disease. It occurs mostly in central and western Africa. Wild rodents and squirrels carry it, but it is called monkeypox because scientists saw it first in lab monkeys. In 2003, it was reported in prairie dogs and humans in the U.S.

Centers for Disease Control and Prevention

Norovirus Infections

Also called: Norwalk virus infections 

Noroviruses are a group of related viruses. Infection with these viruses causes an illness called gastroenteritis, an inflammation of the stomach and intestines. It can spread from person to person, or through contaminated food or water. You can also get it if you touch a contaminated surface. Norovirus can be serious, especially for young children and older adults.

The most common symptoms of norovirus infection are

  • Diarrhea

  • Nausea and vomiting

  • Stomach pain

Other symptoms may include fever, headache or body aches.

Treatment includes bed rest and lots of liquids to prevent dehydration. There is no specific medicine to treat norovirus infections.

Proper hand washing and safe food preparation may help prevent infections.

Polio and Post-Polio Syndrome

Also called: Infantile paralysis, Poliomyelitis, PPS 

Polio is an infectious disease caused by a virus. The virus lives in an infected person's throat and intestines. It is most often spread by contact with the stool of an infected person. You can also get it from droplets if an infected person sneezes or coughs. It can contaminate food and water if people do not wash their hands.

Most people have no symptoms. If you have symptoms, they may include fever, fatigue, nausea, headache, flu-like symptoms, stiff neck and back, and pain in the limbs. A few people will become paralyzed. There is no treatment to reverse the paralysis of polio.

Some people who've had polio develop post-polio syndrome (PPS) years later. Symptoms include tiredness, new muscle weakness, and muscle and joint pain. There is no way to prevent or cure PPS.

The polio vaccine has wiped out polio in the United States and most other countries


Also called: Hemiplegia, Palsy, Paraplegia, Quadriplegia 

Paralysis is the loss of muscle function in part of your body. It happens when something goes wrong with the way messages pass between your brain and muscles. Paralysis can be complete or partial. It can occur on one or both sides of your body. It can also occur in just one area, or it can be widespread. Paralysis of the lower half of your body, including both legs, is called paraplegia. Paralysis of the arms and legs is quadriplegia.

Most paralysis is due to strokes or injuries such as spinal cord injury or a broken neck. Other causes of paralysis include

  • Nerve diseases such as amyotrophic lateral sclerosis

  • Autoimmune diseases such as Guillain-Barre syndrome

  • Bell's palsy, which affects muscles in the face

Polio used to be a cause of paralysis, but polio no longer occurs in the U.S.

Bell's Palsy

Bell's palsy is the most common cause of facial paralysis. It usually affects just one side of the face. Symptoms appear suddenly and are at their worst about 48 hours after they start. They can range from mild to severe and include

  • Twitching

  • Weakness

  • Paralysis

  • Drooping eyelid or corner of mouth

  • Drooling

  • Dry eye or mouth

  • Excessive tearing in the eye

  • Impaired ability to taste

Scientists think that a viral infection makes the facial nerve swell or become inflamed. You are most likely to get Bell's palsy if you are pregnant, diabetic or sick with a cold or flu.

Three out of four patients improve without treatment. With or without treatment, most people begin to get better within 2 weeks and recover completely within 3 to 6 months.


Also called: Hydrophobia 

Rabies is a deadly animal disease caused by a virus. It can happen in wild animals, including raccoons, skunks, bats and foxes, or in dogs, cats or farm animals. People get it from the bite of an infected animal.

In people, symptoms of rabies include fever, headache and fatigue, then confusion, hallucinations and paralysis. Once the symptoms begin, the disease is usually fatal. A series of shots can prevent rabies in people exposed to the virus. You need to get them right away. If an animal bites you, wash the wound well; then get medical care.

To help prevent rabies

  • Vaccinate your pet. Rabies vaccines are available for dogs, cats and farm animals

  • Don't let pets roam

  • Don't approach stray animals. Animals with rabies might be aggressive and vicious, or tired and weak

Animal Bites

Also called: Cat bites, Dog bites 

Wild animals usually avoid people. They might attack, however, if they feel threatened, are sick, or are protecting their young or territory. Attacks by pets are more common. Animal bites rarely are life-threatening, but if they become infected, you can develop serious medical problems.

To prevent animal bites and complications from bites

  • Never pet, handle, or feed unknown animals

  • Leave snakes alone

  • Watch your children closely around animals

  • Vaccinate your cats, ferrets, and dogs against rabies

  • Spay or neuter your dog to make it less aggressive

  • Get a tetanus booster if you have not had one recently

  • Wear boots and long pants when you are in areas with venomous snakes

If an animal bites you, clean the wound with soap and water as soon as possible. Get medical attention if necessary.

Respiratory Syncytial Virus Infections

Also called: RSV 

Respiratory syncytial virus (RSV) causes mild, cold-like symptoms in adults and older healthy children. It can cause serious problems in young babies, including pneumonia and severe breathing problems. Premature babies and those with other health problems have the highest risk. A child with RSV may have a fever, stuffy nose, cough, and trouble breathing. Lab tests can tell if your child has the virus. There is no specific treatment. You should give your child fluids to prevent dehydration. If needed, you can also give a pain reliever (not aspirin) for fever and headache.

RSV easily spreads from person to person. You can get it from direct contact with someone who has it or by touching infected objects such as toys or surfaces such as countertops. Washing your hands often and not sharing eating and drinking utensils are simple ways to help prevent the spread of RSV infection. There is currently no vaccine for RSV.

Rotavirus Infections

Rotavirus is a virus that causes gastroenteritis. Symptoms include severe diarrhea, vomiting, fever, and dehydration. Almost all children in the U.S. are likely to be infected with rotavirus before their 5th birthday.

Infections happen most often in the winter and spring. It is very easy for children with the virus to spread it to other children and sometimes to adults. Once a child gets the virus, it takes about two days to become sick. Vomiting and diarrhea may last from three to eight days.

There is no medicine to treat it. To prevent dehydration, have your child drink plenty of liquids. Your health care provider may recommend oral rehydration drinks. Some children need to go to the hospital for IV fluids. Two vaccines against rotavirus infections are available.


Also called: Verruca 

Warts are growths on your skin caused by an infection with humanpapilloma virus, or HPV. Types of warts include

  • Common warts, which often appear on your fingers

  • Plantar warts, which show up on the soles of your feet

  • Genital warts, which are a sexually transmitted disease

  • Flat warts, which appear in places you shave frequently

In children, warts often go away on their own. In adults, they tend to stay. If they hurt or bother you, or if they multiply, you can remove them. Chemical skin treatments usually work. If not, various freezing, surgical and laser treatments can remove warts

Traveler's Health

Traveling can increase your chances of getting sick. A long flight can increase your risk for deep vein thrombosis. Once you arrive, it takes time to adjust to the water, food, and air in another place. Water in developing countries can contain viruses, bacteria, and parasites that cause stomach upset and diarrhea. Be safe by using only bottled or purified water for drinking, making ice cubes, and brushing your teeth. If you use tap water, boil it or use iodine tablets. Food poisoning can also be a risk. Eat only food that is fully cooked and served hot. Avoid unwashed or unpeeled raw fruits and vegetables.

If you are traveling out of the country, you might also need vaccinations or medicines to prevent specific illnesses. Which ones you need will depend on what part of the world you're visiting, the time of year, your age, overall health status, and previous immunizations. See your doctor 4 to 6 weeks before your trip. Most vaccines take time to become effective.


Screening Tests and Vaccines

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Vaccines can protect you from harmful infections. Some adults think only children need vaccines. But this is not true. For instance, a yearly flu vaccine is recommended for adults of all ages, including healthy adults. You may need certain vaccines because of:

  • Your age

  • Your health or health history

  • Where you live

  • Where your work and the kind of work you do

  • Your lifestyle

Find out what vaccines you may need:

Screening Tests and Vaccines

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Screening tests for women

  • Where do these guidelines come from?

  • Screening tests

  • More information on screening tests for women

Check the guidelines listed here to find out about important screening tests for women. These guidelines are recommended by the U.S. Preventive Services Task Force. Keep in mind that these are guidelines only. Your doctor or nurse will personalize the timing of the screening tests you need based on many factors. Ask your doctor or nurse if you don’t understand why a certain test is recommended for you. Check with your insurance plan to find out which tests are covered. Insurance companies are required to cover many preventive services for women at not cost to you because of the Affordable Care Act.

Where do these guidelines come from?

The screening guidelines listed here are recommended by the U.S. Preventive Services Task Force (USPSTF). The USPSTF is a group of non-Federal experts in prevention (stopping disease before it starts). USPSTF recommendations are evidence-based. This means that science supports USPSTF screening guidelines. The USPSTF is made up of primary care providers (such as internists, pediatricians, family physicians, gynecologists/obstetricians, nurses, and health behavior specialists).

Get regular checkups

Your doctor or nurse can help you stay healthy. Ask your doctor or nurse how often you need to be seen for a routine checkup. Use this time to bring up any health concerns or questions you have. Make sure to ask about:

  • Tobacco use

  • Alcohol use

  • Depression

  • Weight

Screening tests

Screening tests

Ages 18–39

Ages 40–49

Ages 50–64

Ages 65 and older

Blood pressure test

Get tested at least every 2 years if you have normal blood pressure (lower than 120/80).

Get tested once a year if you have blood pressure between 120/80 and 139/89.

Discuss treatment with your doctor or nurse if you have blood pressure 140/90 or higher.

Get tested at least every 2 years if you have normal blood pressure (lower than 120/80).

Get tested once a year if you have blood pressure between 120/80 and 139/89.

Discuss treatment with your doctor or nurse if you have blood pressure 140/90 or higher.

Get tested at least every 2 years if you have normal blood pressure (lower than 120/80).

Get tested once a year if you have blood pressure between 120/80 and 139/89.

Discuss treatment with your doctor or nurse if you have blood pressure 140/90 or higher.

Get tested at least every 2 years if you have normal blood pressure (lower than 120/80).

Get tested once a year if you have blood pressure between 120/80 and 139/89.

Discuss treatment with your doctor or nurse if you have blood pressure 140/90 or higher.

Bone mineral density test
(osteoporosis screening)

Discuss with your doctor or nurse if you are at risk of osteoporosis.

Get this test at least once at age 65 or older.

Talk to your doctor or nurse about repeat testing.

Breast cancer screening

Discuss with your doctor or nurse.

Starting at age 50, get screened every 2 years.

Get screened every 2 years through age 74.

Age 75 and older, ask your doctor or nurse if you need to be screened.

Cervical cancer screening
(Pap test)

Get a Pap test every 3 years if you are 21 or older and have a cervix.

If you are 30 or older, you can get a Pap test and HPV test together every 5 years.

Get a Pap test and HPV test together every 5 years if you have a cervix.

Get a Pap test and HPV test together every 5 years if you have a cervix.

Ask your doctor or nurse if you need to get a Pap test.

Chlamydia test

Get tested for chlamydia yearly through age 24 if you are sexually active or pregnant.

Age 25 and older, get tested for chlamydia if you are at increased risk, pregnant or not pregnant.

Get tested for chlamydia if you are sexually active and at increased risk, pregnant or not pregnant.

Get tested for chlamydia if you are sexually active and at increased risk.

Get tested for chlamydia if you are sexually active and at increased risk.

Cholesterol test

Starting at age 20, get a cholesterol test regularly if you are at increased risk for heart disease.

Ask your doctor or nurse how often you need your cholesterol tested.

Get a cholesterol test regularly if you are at increased risk for heart disease.

Ask your doctor or nurse how often you need your cholesterol tested.

Get a cholesterol test regularly if you are at increased risk for heart disease.

Ask your doctor or nurse how often you need your cholesterol tested.

Get a cholesterol test regularly if you are at increased risk for heart disease.

Ask your doctor or nurse how often you need your cholesterol tested.

Colorectal cancer screening
(using fecal occult blood testing, sigmoidoscopy, or colonoscopy)

Starting at age 50, get screened for colorectal cancer.

Talk to your doctor or nurse about which screening test is best for you and how often you need it.

Get screened for colorectal cancer through age 75.

Talk to your doctor or nurse about which screening test is best for you and how often you need it.

Diabetes screening

Get screened for diabetes if your blood pressure is higher than 135/80 or if you take medicine for high blood pressure.

Get screened for diabetes if your blood pressure is higher than 135/80 or if you take medicine for high blood pressure.

Get screened for diabetes if your blood pressure is higher than 135/80 or if you take medicine for high blood pressure.

Get screened for diabetes if your blood pressure is higher than 135/80 or if you take medicine for high blood pressure.

Gonorrhea test

Get tested for gonorrhea if you are sexually active and at increased risk, pregnant or not pregnant.

Get tested for gonorrhea if you are sexually active and at increased risk, pregnant or not pregnant.

Get tested for gonorrhea if you are sexually active and at increased risk.

Get tested for gonorrhea if you are sexually active and at increased risk.

HIV test

Get tested for HIV at least once.

Discuss your risk with your doctor or nurse because you may need more frequent tests.

All pregnant women need to be tested for HIV.

Get tested for HIV at least once.

Discuss your risk with your doctor or nurse because you may need more frequent tests.

All pregnant women need to be tested for HIV.

Get tested for HIV at least once.

Discuss your risk with your doctor or nurse because you may need more frequent tests.

Get tested for HIV at least once if you are age 65 and have never been tested.

Get tested if you are at increased risk for HIV.

Discuss your risk with your doctor or nurse.

Syphilis test

Get tested for syphilis if you are at increased risk or pregnant.

Get tested for syphilis if you are at increased risk or pregnant.

Get tested for syphilis if you are at increased risk.

Get tested for syphilis if you are at increased risk.

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Screening tests for men

  • Where do these guidelines come from?

  • Screening tests

  • More information on screening tests for men

Check the guidelines listed here to find out about important screening tests for men. Keep in mind that these are guidelines only. Your doctor or nurse will personalize the timing of the screening tests you need based on many factors. Ask your doctor or nurse if you don't understand why a certain test is recommended for you. Check with your insurance plan to find out which tests are covered.

Where do these guidelines come from?

The screening guidelines listed here are recommended by the U.S. Preventive Services Task Force (USPSTF). The USPSTF is a group of non-Federal experts in prevention (stopping disease before it starts). USPSTF recommendations are evidence-based. This means that science supports USPSTF screening guidelines. The USPSTF is made up of primary care providers (such as internists, pediatricians, family physicians, gynecologists/obstetricians, nurses, and health behavior specialists).

Get regular checkups

Your doctor or nurse can help you stay healthy. Ask your doctor or nurse how often you need to be seen for a routine checkup. Use this time to bring up any health concerns or questions you have. Make sure to ask about:

  • Tobacco use

  • Alcohol use

  • Depression

  • Weight

Screening tests

Screening tests

Ages 18–39

Ages 40–49

Ages 50–64

Ages 65 and older

Abdominal aortic aneurysm screening

Get this one-time screening if you are age 65 to 75 and have ever smoked.

Blood pressure test

Get tested at least every 2 years if you have normal blood pressure (lower than 120/80).

Get tested once a year if you have blood pressure between 120/80 and 139/89.

Discuss treatment with your doctor or nurse if you have blood pressure 140/90 or higher.

Get tested at least every 2 years if you have normal blood pressure (lower than 120/80).

Get tested once a year if you have blood pressure between 120/80 and 139/89.

Discuss treatment with your doctor or nurse if you have blood pressure 140/90 or higher.

Get tested at least every 2 years if you have normal blood pressure (lower than 120/80).

Get tested once a year if you have blood pressure between 120/80 and 139/89.

Discuss treatment with your doctor or nurse if you have blood pressure 140/90 or higher.

Get tested at least every 2 years if you have normal blood pressure (lower than 120/80).

Get tested once a year if you have blood pressure between 120/80 and 139/89.

Discuss treatment with your doctor or nurse if you have blood pressure 140/90 or higher.

Cholesterol test

Starting at age 20 until age 35, get a cholesterol test if you are at increased risk for heart disease.

Starting at age 35 and older, get a cholesterol test regularly.

Ask your doctor or nurse how often you need your cholesterol tested.

Get a cholesterol test regularly.

Ask your doctor or nurse how often you need your cholesterol tested.

Get a cholesterol test regularly.

Ask your doctor or nurse how often you need your cholesterol tested.

Get a cholesterol test regularly.

Ask your doctor or nurse how often you need your cholesterol tested.

Colorectal cancer screening
(using fecal occult blood testing, sigmoidoscopy, or colonoscopy)

Starting at age 50, get screened for colorectal cancer.

Talk to your doctor or nurse about which screening test is best for you and how often you need it.

Get screened for colorectal cancer through age 75.

Talk to your doctor or nurse about which screening test is best for you and how often you need it.

Diabetes screening

Get screened for diabetes if your blood pressure is higher than 135/80 or if you take medicine for high blood pressure.

Get screened for diabetes if your blood pressure is higher than 135/80 or if you take medicine for high blood pressure.

Get screened for diabetes if your blood pressure is higher than 135/80 or if you take medicine for high blood pressure.

Get screened for diabetes if your blood pressure is higher than 135/80 or if you take medicine for high blood pressure.

HIV test

Get tested if you are at increased risk for HIV.

Discuss your risk with your doctor or nurse.

Get tested if you are at increased risk for HIV.

Discuss your risk with your doctor or nurse.

Get tested if you are at increased risk for HIV.

Discuss your risk with your doctor or nurse.

Get tested if you are at increased risk for HIV.

Discuss your risk with your doctor or nurse.

Syphilis screening

Get tested for syphilis if you are at increased risk.

Get tested for syphilis if you are at increased risk.

Get tested for syphilis if you are at increased risk.

Get tested for syphilis if you are at increased risk.

More information on Screening tests for men

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Glossaries and Medical Terminologies

Vaccine Glossary of Terms


Acellular vaccine:
A vaccine containing partial cellular material as opposed to complete cells.

Acquired Immune Deficiency Syndrome (AIDS): A medical condition where the immune system cannot function properly and protect the body from disease. As a result, the body cannot defend itself against infections (like pneumonia). AIDS is caused by the Human Immunodeficiency Virus (HIV). This virus is spread through direct contact with the blood and body fluids of an infected individual. High risk activities include unprotected sexual intercourse and intravenous drug use (sharing needles). There is no cure for AIDS, however, research efforts are on-going to develop a vaccine.

Active immunity: The production of antibodies against a specific disease by the immune system. Active immunity can be acquired in two ways, either by contracting the disease or through vaccination. Active immunity is usually permanent, meaning an individual is protected from the disease for the duration of their lives.

A short-term, intense health effect.

A substance (e.g. aluminum salt) that is added during production to increase the body's immune response to a vaccine.

Adverse events: Undesirable experiences occurring after immunization that may or may not be related to the vaccine.

Advisory Committee on Immunization Practices (ACIP): A panel of 10 experts who make recommendations on the use of vaccines in the United States. The panel is advised on current issues by representatives from the Centers for Disease Control and Prevention, Food and Drug Administration, National Institutes of Health, American Academy of Pediatrics, American Academy of Family Physicians, American Medical Association and others. The recommendations of the ACIP guide immunization practice at the federal, state and local level.

Allergy: A condition in which the body has an exaggerated response to a substance (e.g. food or drug). Also known as hypersensitivity.

An immediate and severe allergic reaction to a substance (e.g. food or drugs). Symptoms of anaphylaxis include breathing difficulties, loss of consciousness and a drop in blood pressure. This condition can be fatal and requires immediate medical attention.

An acute infectious disease caused by the spore-forming bacterium Bacillus anthracis. Anthrax most commonly occurs in hoofed mammals and can also infect humans.

A substance that fights bacteria.

A protein found in the blood that is produced in response to foreign substances (e.g. bacteria or viruses) invading the body. Antibodies protect the body from disease by binding to these organisms and destroying them.

Foreign substances (e.g. bacteria or viruses) in the body that are capable of causing disease. The presence of antigens in the body triggers an immune response, usually the production of antibodies.

Antibodies capable of destroying toxins generated by microorganisms including viruses and bacteria.

Antiviral: Literally "against-virus" -- any medicine capable of destroying or weakening a virus.

Joint pain.

Arthritis: A medical condition characterized by inflammation of the joints which results in pain and difficulty moving.

Association: The degree to which the occurrence of two variables or events is linked. Association describes a situation where the likelihood of one event occurring depends on the presence of another event or variable. However, an association between two variables does not necessarily imply a cause and effect relationship. The term association and relationship are often used interchangeably. See causal and temporal association.

Asthma: A chronic medical condition where the bronchial tubes (in the lungs) become easily irritated. This leads to constriction of the airways resulting in wheezing, coughing, difficulty breathing and production of thick mucus. The cause of asthma is not yet known but environmental triggers, drugs, food allergies, exercise, infection and stress have all been implicated.

Asymptomatic infection:
The presence of an infection without symptoms. Also known as inapparent or subclinical infection.

Attenuated vaccine:
A vaccine in which live virus is weakened through chemical or physical processes in order to produce an immune response without causing the severe effects of the disease. Attenuated vaccines currently licensed in the United States include measles, mumps, rubella, polio, yellow fever and varicella. Also known as a live vaccine.

Autism: A chronic developmental disorder usually diagnosed between 18 and 30 months of age. Symptoms include problems with social interaction and communication as well as repetitive interests and activities. At this time, the cause of autism is not known although many experts believe it to be a genetically based disorder that occurs before birth.


B cells: Small white blood cells that help the body defend itself against infection. These cells are produced in bone marrow and develop into plasma cells which produce antibodies. Also known as B lymphocytes.

Bacteria: Tiny one-celled organisms present throughout the environment that require a microscope to be seen. While not all bacteria are harmful, some cause disease. Examples of bacterial disease include diphtheria, pertussis, tetanus, Haemophilus influenzae, and pneumococcal.

Bias: Flaws in the collection, analysis or interpretation of research data that lead to incorrect conclusions.

Biological plausibility: A causal association (or relationship between two factors) is consistent with existing medical knowledge.

Bone marrow: Soft tissue located within bones that produce all blood cells, including the ones that fight infection.

Booster shots: Additional doses of a vaccine needed periodically to "boost" the immune system. For example, the tetanus and diphtheria (Td) vaccine which is recommended for adults every ten years.

Brachial neuritis:
Inflammation of nerves in the arm causing muscle weakness and pain.

Breakthrough infection: Development of a disease despite a person's having responded to a vaccine.


Causal association:
The presence or absence of a variable (e.g. smoking) is responsible for an increase or decrease in another variable (e.g. cancer). A change in exposure leads to a change in the outcome of interest.

Chickenpox: See Varicella.

Chronic health condition: A health related state that lasts for a long period of time (e.g. cancer, asthma).

Combination vaccine: Two or more vaccines administered in a single dose in order to reduce the number of shots given. For example, the MMR (measles, mumps, rubella) vaccine.

Communicable: That which can be transmitted from one person or animal to another. Also known as infectious.

Crohn's disease:
A chronic medical condition characterized by inflammation of the bowel. Symptoms include abdominal pain, diarrhea, fever, loss of appetite and weight loss. The cause of Crohn's disease is not yet known, but genetic, dietary and infectious factors may play a part.

Community immunity: A situation in which a sufficient proportion of a population is immune to an infectious disease (through vaccination and/or prior illness) to make its spread from person to person unlikely. Even individuals not vaccinated (such as newborns and those with chronic illnesses) are offered some protection because the disease has little opportunity to spread within the community. Also known as herd immunity.

Conjugate vaccine:
The joining together of two compounds (usually a protein and polysaccharide) to increase a vaccine's effectiveness.

Inflammation of the mucous membranes surrounding the eye causing the area to become red and irritated. The membranes may be irritated because of exposure to heat, cold or chemicals. This condition is also caused by viruses, bacteria or allergies.

A condition in a recipient which is likely to result in a life-threatening problem if a vaccine were given.

Convulsion: See Seizure.

Crib or Cot Death: See Sudden Infant Death Syndrome (SIDS)


A muscle in the upper arm where shots are usually given.

Demyelinating disorders:
A medical condition where the myelin sheath is damaged. The myelin sheath surrounds nerves and is responsible for the transmission of impulses to the brain. Damage to the myelin sheath results in muscle weakness, poor coordination and possible paralysis. Examples of demyelinating disorders include Multiple Sclerosis (MS), optic neuritis, transverse neuritis and Guillain-Barre Syndrome (GBS).

Diabetes: A chronic health condition where the body is unable to produce insulin and properly breakdown sugar (glucose) in the blood. Symptoms include hunger, thirst, excessive urination, dehydration and weight loss. The treatment of diabetes requires daily insulin injections, proper nutrition and regular exercise. Complications can include heart disease, stroke, neuropathy, poor circulation leading to loss of limbs, hearing impairment, vision problems and death.

A bacterial disease marked by the formation of a false membrane, especially in the throat, which can cause death.

Disease: Sickness, illness or loss of health.


Efficacy rate:
A measure used to describe how good a vaccine is at preventing disease.

Inflammation of the brain caused by a virus. Encephalitis can result in permanent brain damage or death.

A general term describing brain dysfunction. Examples include encephalitis, meningitis, seizures and head trauma.

The occurrence of disease within a specific geographical area or population that is in excess of what is normally expected.

The continual, low-level presence of disease in a community

Erythema Multiforme:
A medical condition characterized by inflammation of the skin or mucous membranes (including the mouth, throat and eyes). Erthema Multiforme has been reported following infection. Symptoms persist anywhere from 2 days to 4 weeks and include skin lesions, blisters, itching, fatigue, joint pain and fever.

The cause of.

Exposure: Contact with infectious agents (bacteria or viruses) in a manner that promotes transmission and increases the likelihood of disease.


Relating to fever; feverish.


Guillain-Barre Syndrome (GBS):
A rare neurological disease characterized by loss of reflexes and temporary paralysis. Symptoms include weakness, numbness, tingling and increased sensitivity that spreads over the body. Muscle paralysis starts in the feet and legs and moves upwards to the arms and hands. Sometimes paralysis can result in the respiratory muscles causing breathing difficulties. Symptoms usually appear over the course of one day and may continue to progress for 3 or 4 days up to 3 or 4 weeks. Recovery begins within 2-4 weeks after the progression stops. While most patients recover, approximately 15%-20% experience persistent symptoms. GBS is fatal in 5% of cases.


Haemophilus influenzae type b (Hib):
A bacterial infection that may result in severe respiratory infections, including pneumonia, and other diseases such as meningitis.

Hepatitis A: A minor viral disease, that usually does not persist in the blood; transmitted through ingestion of contaminated food or water.

Hepatitis B: A viral disease transmitted by infected blood or blood products, or through unprotected sex with someone who is infected.

Hepatitis C: is a liver disease caused by the Hepatitis C virus (HCV), which is found in the blood of persons who have the disease. HCV is spread by contact with the blood of an infected person.

Hepatitis D: is a defective virus that needs the hepatitis B virus to exist. Hepatitis D virus (HDV) is found in the blood of persons infected with the virus.

Hepatitis E: is a virus (HEV) transmitted in much the same way as hepatitis A virus. Hepatitis E, however, does not often occur in the United States.

Herd immunity: See Community immunity.

Herpes Zoster: A disease characterized by painful skin lesions that occur mainly on the trunk (back and stomach) of the body but which can also develop on the face and in the mouth. Complications include headache, vomiting, fever and meningitis. Recovery may take up to 5 weeks. Herpes Zoster is caused by the same virus that is responsible for chickenpox. Most people are exposed to this virus during childhood. After the primary infection (chickenpox), the virus becomes dormant, or inactivated. In some people the virus reactivates years, or even decades, later and causes herpes zoster. Also known as the shingles.

Hives: The eruption of red marks on the skin that are usually accompanied by itching. This condition can be caused by an allergy (e.g. to food or drugs), stress, infection or physical agents (e.g. heat or cold). Also known as uticaria.

A condition in which the body has an exaggerated response to a substance (e.g. food or drug). Also known as an allergy.

A condition in which the body has a weakened or delayed reaction to a substance.


Immune globulin:
A protein found in the blood that fights infection. Also known as gamma globulin.

Immune system: The complex system in the body responsible for fighting disease. Its primary function is to identify foreign substances in the body (bacteria, viruses, fungi or parasites) and develop a defense against them. This defense is known as the immune response. It involves production of protein molecules called antibodies to eliminate foreign organisms that invade the body.

Immunity: Protection against a disease. There are two types of immunity, passive and active. Immunity is indicated by the presence of antibodies in the blood and can usually be determined with a laboratory test. See active and passive immunity

The process by which a person or animal becomes protected against a disease. This term is often used interchangeably with vaccination or inoculation.

When the immune system is unable to protect the body from disease. This condition can be caused by disease (like HIV infection or cancer) or by certain drugs (like those used in chemotherapy). Individuals whose immune systems are compromised should not receive live, attenuated vaccines.

Inactivated vaccine:
A vaccine made from viruses and bacteria that have been killed through physical or chemical processes. These killed organisms cannot cause disease.

Inapparent infection: The presence of infection without symptoms. Also known as subclinical or asymptomatic infection.

Incidence: The number of new disease cases reported in a population over a certain period of time.

Incubation period: The time from contact with infectious agents (bacteria or viruses) to onset of disease.

Infectious: Capable of spreading disease. Also known as communicable.

Infectious agents: Organisms capable of spreading disease (e.g. bacteria or viruses).

Inflammation: Redness, swelling, heat and pain resulting from injury to tissue (parts of the body underneath the skin). Also known as swelling.

Inflammatory Bowel Disease (IBD): A general term for any disease characterized by inflammation of the bowel. Examples include colitis and Crohn's disease. Symptoms include abdominal pain, diarrhea, fever, loss of appetite and weight loss.

Influenza: A highly contagious viral infection characterized by sudden onset of fever, severe aches and pains, and inflammation of the mucous membrane.

Investigational vaccine: A vaccine that has been approved by the Food and Drug Administration (FDA) for use in clinical trials on humans. However, investigational vaccines are still in the testing and evaluation phase and are not licensed for use in the general public. 


Yellowing of the skin and eyes. This condition is often a symptom of hepatitis infection.


An abnormal change in the structure of an organ, due to injury or disease.

Live vaccine: A vaccine in which live virus is weakened (attenuated) through chemical or physical processes in order to produce an immune response without causing the severe effects of the disease. Attenuated vaccines currently licensed in the United States include measles, mumps, rubella, shingles (herpes zoster), varicella, and yellow fever. Also known as an attenuated vaccine.

Lupus: A disease characterized by inflammation of the connective tissue (which supports and connects all parts of the body). Chronic swelling of the connective tissue causes damage to the skin, joints, kidneys, nervous system and mucous membranes. The disease begins with fever, joint pain and fatigue. Additional symptoms continue to develop over the years including nausea, fatigue, weight loss, arthritis, headaches and epilepsy. Problems with heart, lung and kidney function may also result. This condition is diagnosed most frequently in young women but also occurs in children.

Lyme disease: A bacterial disease transmitted by infected ticks. Human beings may come into contact with infected ticks during outdoor activities (camping, hiking). Symptoms include fatigue, chills, fever, headache, joint and muscle pain, swollen lymph nodes and a skin rash (in a circular pattern). Long-term problems include arthritis, nervous system abnormalities, irregular heart rhythm and meningitis. Lyme disease can be treated with antibiotics. A vaccine was available from 1998 to 2002.

Lymphocytes: Listen[MP3-95 KB]
Small white blood cells that help the body defend itself against infection. These cells are produced in bone marrow and develop into plasma cells which produce antibodies. Also known as B cells.


A large cell that helps the body defend itself against disease by surrounding and destroying foreign organisms (viruses or bacteria).

Skin lesions, normally red-colored.

Measles: A contagious viral disease marked by the eruption of red circular spots on the skin.

Memory Cell: A group of cells that help the body defend itself against disease by remembering prior exposure to specific organisms (e.g. viruses or bacteria). Therefore these cells are able to respond quickly when these organisms repeatedly threaten the body.

Inflammation of the brain and spinal cord that can result in permanent brain damage and death.

["men in joe en sef uh LIGHT iss"] -- inflammation of the brain and meninges (membranes) that involves the encephalon (area inside the skull) and spinal column.

Tiny organisms (including viruses and bacteria) that can only be seen with a microscope.

Mucosal membranes:
The soft, wet tissue that lines body openings specifically the mouth, nose, rectum and vagina.

Multiple Sclerosis:
Multiple sclerosis (MS) is a disease of the central nervous system characterized by the destruction of the myelin sheath surrounding neurons, resulting in the formation of "plaques." MS is a progressive and usually fluctuating disease with exacerbations (patients feeling worse) and remissions (patients feeling better) over many decades. Eventually, in most patients, remissions do not reach baseline levels and permanent disability and sometimes death occurs. The cause of MS is unknown. The most widely held hypothesis is that MS occurs in patients with a genetic susceptibility and that some environmental factors "trigger" exacerbations. MS is 3 times more common in women than men, with diagnosis usually made as young adults. Also see demyelinating disorders.

Mumps: Acute contagious viral illness marked by swelling, especially of the parotid glands.


Inflammation of the nerves.

A general term for any dysfunction in the peripheral nervous system. Symptoms include pain, muscle weakness, numbness, loss of coordination and paralysis. This condition may result in permanent disability.


Optic neuritis:
A medical condition where vision deteriorates rapidly over hours or days. One or both eyes may be affected. This condition results for the demyelination of optic nerves. In most cases, the cause of optic neuritis is unknown. Patients may regain their vision or be left with permanent impairment. Also see demyelinating disorders.


A complication of mumps infection occurring in males (who are beyond puberty). Symptoms begin 7-10 days after onset of mumps and include inflammation of the testicles, headache, nausea, vomiting, pain and fever. Most patients recover but in rare cases sterility occurs.

Otitis Media:
A viral or bacterial infection that leads to inflammation of the middle ear. This condition usually occurs along with an upper respiratory infection. Symptoms include earache, high fever, nausea, vomiting and diarrhea. In addition, hearing loss, facial paralysis and meningitis may result.

Outbreak: Sudden appearance of a disease in a specific geographic area (e.g. neighborhood or community) or population (e.g., adolescents).


Pandemic: An epidemic occurring over a very large geographic area.

Marked by small red-colored elevation of the skin.

Passive immunity: Protection against disease through antibodies produced by another human being or animal. Passive immunity is effective, but protection is generally limited and diminishes over time (usually a few weeks or months). For example, maternal antibodies are passed to the infant prior to birth. These antibodies temporarily protect the baby for the first 4-6 months of life.

Pathogens: Organisms (e.g. bacteria, viruses, parasites and fungi) that cause disease in human beings.

(whooping cough) Bacterial infectious disease marked by a convulsive spasmodic cough, sometimes followed by a crowing intake of breath.

["pe TEEK ee ay"] -- a tiny reddish or purplish spot on the skin or mucous membrane, commonly part of infectious diseases such as typhoid fever.

Placebo: A substance or treatment that has no effect on human beings.

Inflammation of the lungs characterized by fever, chills, muscle stiffness, chest pain, cough, shortness of breath, rapid heart rate and difficulty breathing.

(polio) An acute infectious viral disease characterized by fever, paralysis, and atrophy of skeletal muscles.

Polysaccharide vaccines:
Vaccines that are composed of long chains of sugar molecules that resemble the surface of certain types of bacteria. Polysaccharide vaccines are available for pneumococcal disease, meningococcal disease and Haemophilus Influenzae type b.

Potency: A measure of strength.

Precaution: A condition in a recipient which may result in a life-threatening problem if the vaccine is given, or a condition which could compromise the ability of the vaccine to produce immunity.

Prevalence: The number of disease cases (new and existing) within a population over a given time period.

An early symptom indicating the onset of an attack or a disease.


Quarantine: The isolation of a person or animal who has a disease (or is suspected of having a disease) in order to prevent further spread of the disease.


Of or resulting from new combinations of genetic material or cells; the genetic material produced when segments of DNA from different sources are joined to produce recombinant DNA.

Reye Syndrome:
Encephalopathy (general brain disorder) in children following an acute illness such as influenza or chickenpox. Symptoms include vomiting, agitation and lethargy. This condition may result in coma or death.

Residual Seizure Disorder (RSD): See seizures.

Risk: The likelihood that an individual will experience a certain event.

A group of viruses that cause diarrhea in children.

Rubella: (German measles) Viral infection that is milder than normal measles but as damaging to the fetus when it occurs early in pregnancy.

See Measles.


Development of antibodies in the blood of an individual who previously did not have detectable antibodies.

Measurement of antibodies, and other immunological properties, in the blood serum.

Study measuring a person's risk of developing a particular disease.

Seizure: The sudden onset of a jerking and staring spell usually caused by fever. Also known as convulsions.

Severe Combined immune Deficiency (SCID): Included in a group of rare, life-threatening disorders caused by at least 15 different single gene defects that result in profound deficiencies in T- and B- lymphocyte function.

Shingles: See herpes zoster.

Side Effect: Undesirable reaction resulting from immunization

Smallpox: An acute, highly infectious, often fatal disease caused by a poxvirus and characterized by high fever and aches with subsequent widespread eruption of pimples that blister, produce pus, and form pockmarks. Also called variola.

Strain: A specific version of an organism. Many diseases, including HIV/AIDS and hepatitis, have multiple strains.

Subclinical infection: The presence of infection without symptoms. Also known as inapparent or asymptomatic infection.

Sudden Infant Death Syndrome (SIDS): The sudden and unexpected death of a healthy infant under 1 year of age. A diagnosis of SIDS is made when an autopsy cannot determine another cause of death. The cause of SIDS is unknown. Also known as "crib" or "cot" death.

Susceptible: Unprotected against disease.


Temporal association: Two or more events that occur around the same time but may be unrelated, chance occurrences.

Of, relating to, or causing developmental malformations.

Toxin-producing bacterial disease marked by painful muscle spasms.

Thimerosal is a mercury-containing preservative used in some vaccines and other products since the 1930's. There is no convincing evidence of harm caused by the low concentrations of thimerosal in vaccines, except for minor reactions like redness and swelling at the injection site. However, in July 1999, the Public Health Service agencies, the American Academy of Pediatrics, and vaccine manufacturers agreed that thimerosal should be reduced or eliminated in vaccines as a precautionary measure. Today, all routinely recommended childhood vaccines manufactured for the U.S. market contain either no thimerosal or only trace amounts with the exception of some flu vaccines. There are thimerosal-free influenza vaccines available.

Typhoid Fever: Typhoid fever is a life-threatening illness caused by the bacterium Salmonella Typhi. Persons with typhoid fever carry the bacteria in their bloodstream and intestinal tract.

The detection of antibodies in blood through a laboratory test.

Transverse Myelitis: ]
The sudden onset of spinal cord disease. Symptoms include general back pain followed by weakness in the feet and legs that moves upward. There is no cure and many patients are left with permanent disabilities or paralysis. Transverse Myelitis is a demyelinating disorder that may be associated with Multiple Sclerosis (MS). Also see demyelinating disorders.


The eruption of red marks on the skin that are usually accompanied by itching. This condition can be caused by an allergy (e.g. to food or drugs), stress, infection or physical agents (e.g. heat or cold). Also known as hives.


Injection of a killed or weakened infectious organism in order to prevent the disease.

A virus related to the smallpox and cowpox viruses, which is used in smallpox vaccine.

A product that produces immunity therefore protecting the body from the disease. Vaccines are administered through needle injections, by mouth and by aerosol.

Vaccine Adverse Event Reporting System (VAERS): A database managed by the Centers for Disease Control and Prevention and the Food and Drug Administration. VAERS provides a mechanism for the collection and analysis of adverse events associated with vaccines currently licensed in the United States. Reports to VAERS can be made by the vaccine manufacturer, recipient, their parent/guardian or health care provider. For more information on VAERS call (800) 822-7967.

Vaccine Safety Datalink Project (VSD): In order to increase knowledge about vaccine adverse events, the Centers for Disease Control and Prevention have formed partnerships with eight large Health Management Organizations (HMOs) to continually evaluate vaccine safety. The project contains data on more than 6 million people. Medical records are monitored for potential adverse events following immunization. The VSD project allows for planned vaccine safety studies as well as timely investigations of hypothesis.

(Chickenpox) -- An acute contagious disease characterized by papular and vesicular lesions.

See smallpox.

Characterized by small elevations of the skin containing fluid (blisters).

The presence of a virus in the blood.

The relative capacity of a pathogen to overcome body defenses.

Virus: A tiny organism that multiplies within cells and causes disease such as chickenpox, measles, mumps, rubella, pertussis and hepatitis. Viruses are not affected by antibiotics, the drugs used to kill bacteria.


Waning Immunity: The loss of protective antibodies over time.

Whooping Cough:

FDA Glossary of Terms


Abbreviated New Drug Application (ANDA)

The ANDA was established by the Waxman-Hatch Act. Under an ANDA, proof of bioequivalence is enough to satisfy FDA safety and efficacy requirements for a generic drug. In addition, the manufacturer of the generic must certify that the original drug is either (a) not patented, (b) has an expired patent, (c) has a patent expiry date before which the generic will not be sold, or (d) has an invalid patent or a patent that the generic does not infringe. If the manufacturer claims the original patent is invalid or not infringed, there is a thirty-month litigation period during which the FDA cannot approve the generic.

A-B-C-D Health Claims Categories

A-B-C-D Health Claim Categories refer to a scoring method by which health claims manufacturers can be measured based on the amount of supporting evidence. Since September 2003 the FDA has accepted applications for health claims from food items using a form of the A-B-C-D system where “A” represents “significant scientific agreement” and “D” represents “little scientific evidence supporting this claim.” Proponents believe this has allowed food producers to advertise benefits that have not met the FDAs proof-of-efficacy requirements. One option for labeling reform is that the FDA could accept similar qualified claims of health benefits from drugs.

As of 2008 the FDA has currently approved 12 health claims, while allowing 16 qualified health claims. The number of petitioned claims is uncertain. As of late 2007, members of Congress were calling for a halt of qualified health claims until a GAO study could be completed and had prompted the FDA to conduct a re-evaluation of a number of pre-existing qualified health claims, but no such halt has taken place.

In 2006 the European Union passed regulation electing to implement health benefit claims on food without a report card but with specific requirements for various claims that will be assessed by the national authority of a member state. It has since provided additional guidance on implementing the regulation.

The implementation of the food health claims categories, in response to a court decision from Pearson v. Shalala requiring the allowance of qualified health claims, has liberalized dietary supplement food sales by enabling producers to advertise and differentiate their products without meeting the FDA criteria for significant scientific agreement. However, the FDA still determines the grade received by a health claim, and therefore retains a form of pre-market approval of these qualified health claims.

Research has suggested that the distinctions as used in the food health claim labels have proven unclear to consumers in testing (IFIC, 2005, Derby and Levy, 2005, Teratanavat, 2005). The most recent GAO study notes that some organizations such as the American Medical Association, have called for the elimination of qualified health claims on the grounds that consumers cannot distinguish between the four existing categories.

Accelerated Development

After the IND has been filed, a drug that can be used by patients who are suffering from life-threatening or seriously debilitating conditions, for which no other drug treatment exists, can qualify for accelerated development. Approval can be based on surrogate endpoints or on an FDA determination that the drug can be used safely if distribution is limited.


Aspirin has been called the wonder drug of the twentieth century. It is used extensively in the treatment of mild to moderate pain, fever, and inflammation, and has also been discovered to be useful in the management and prevention of heart attacks and strokes (which are off-label uses) and perhaps also of colon cancer and other maladies. For many years, the FDA prohibited manufacturers from advertising or promoting the use of aspirin for heart attack victims, a decision that was responsible for thousands of needless deaths (see the section Advertising Restrictions). The FDA continues to prevent manufacturers from advertising and promoting some of aspirin’s many uses.

Luckily for Americans, aspirin was available in the United States long before the modern FDA (aspirin was known to Hippocrates, although that knowledge was lost and not rediscovered until the late eighteenth century). Given the FDA’s dangerously risk-averse attitude and its reliance on animal studies, many people have speculated that aspirin would not be approved by the FDA if it were discovered today(see, for example, Wardell and Lasagna 1975, 137–39). Although aspirin is in general a very safe drug, it can cause stomach bleeding and is responsible for some seven thousand deaths and seventy-six thousand hospitalizations per year in the United States (Grinspoon 1997). In addition, aspirin, along with a number of other familiar drugs such as penicillin, produces very negative effects in some laboratory animals. All of this leads us to the question, How many wonder drugs have we lost because of the FDA’s deadly overcaution?

Assurance of Quality and Safety

Consumers want quality and safety in their drugs and devices. Moreover, consumers, prior to purchase and use, want assurance of quality and safety. Society has three broad approaches to quality and safety assurance. The first is voluntary practices and institutions—such as reputation, knowers, and middlemen—which assure quality and safety because it is almost always unprofitable to harm or cheat the customer. The second is tort remedy, by which consumers who are harmed or cheated may litigate under the tort doctrines of fraud, negligence, breach of contract, and so on. The third is governmentally imposed restrictions on voluntary exchange, whereby government attempts to determine the quality and safety of goods and services, and prohibits exchange until it has given permission. The FDA represents the third approach, which is the only approach that entails coercion against innocent parties. The theme of this Web page is that the best way to meet the demand for assurance is the combination of voluntary means and the tort system. We argue that the third approach, government restriction, does not achieve anything beyond what would be achieved by the other two approaches, yet prevents people from consummating many important and legitimate activities and exchanges. We argue, essentially, that the demand for assurance, like the demand for clothing, is best met by the free-enterprise system working within a sensible tort system.

Baby Ventilator Incident

Krauss (1996) explains: “[In the early 1990s, the FDA] ordered hospitals to stop using specialized baby ventilators, which are irreplaceable in saving sick infants because they provide uniquely tiny breaths of air, because hospitals refused to ‘blind-test’ them and thereby condemn[ed] fifty percent of air-deprived infants. Dr. Martin Kessler of Georgetown University Medical Center estimates that scores of babies died as a result. Subsequent to the FDA decision, protest from doctors who pointed to named infants’ deaths were aired on the [ABC] television show ‘20/20’ [“So Safe You Could Die—Overregulation by the FDA,” broadcast 12 August 1994]. Only then did the agency again allow use of the ventilators” (468–69).

This incident (see also Some Remarks about Medical Devices) illustrate what it takes to pry permission from the FDA stranglehold. The special circumstances that made the public-information campaign successful in this case are, tragically, extremely rare. Usually, doctors are not able to identify the victims of the FDA’s withholding of new therapies.

Biological Drugs

Biological drugs (or biologics) such as insulin, penicillin, blood and blood products, vaccines, derivatives of natural substances, and extracts of living cells are grown or cultured in separate batches. Just as with beer or wine, the quality can vary considerably by batch depending on small differences in inputs. Thus, in addition to obtaining marketing approval, a biologics manufacturer previously also had to have its production methods and facilities FDA licensed. Moreover, every batch of biologics had to be FDA tested. Recent advances in biotechnology, however, have diminished the variation and made production more like that of nonbiological (or chemically synthesized) drugs. In 1995, the FDA announced simplified rules on “well-characterized” biologics, dropping manufacturing-facility licensing and batch certification in such cases. Today many biologics are treated in the same fashion as nonbiological drugs. The FDA’s rules on biologics were codified in the 1997 Modernization Act.

Breast Implants

In 1992, journalists highlighted claims by women that their silicone breast implants caused connective tissue diseases. Without clinical tests or clear scientific evidence, the FDA banned most implants and crusaded against the industry, leading to a $3.2 billion court settlement that drove manufacturer Dow Corning into bankruptcy. Studies by the University of Michigan, the University of Maryland, the Mayo Clinic, the Harvard Medical School, the American Medical Association, and others, however, have found no causal link between implants and connective tissue diseases. An independent panel of experts commissioned by the British government concluded that “Silicone gel breast implants are not associated with any greater health risk than other surgical implants.” And “In particular, there is no evidence of an association with an abnormal immune response or typical or atypical connective tissue diseases or syndromes.” The British study (Silicone Gel Breast Implants: The Report of the Independent Review Group [London: Department of Health, 1998]) references previous reviews and the voluminous scientific literature. Angell (1997) is an accessible yet scientifically accurate account of the breast implants controversy.

Brief Summary

The brief summary is a technical document written for physicians and other health care professionals that the FDA requires to accompany an advertisement for a drug. It is typically a page in length, written in small, often illegible print and is so technical that it is virtually incomprehensible to consumers. The brief summary is not required if the advertisement mentions the name of the drug but not the use or if the remedy is mentioned without the name of the drug. Because the brief summary typically requires an additional page in a printed ad or additional airtime in a TV or radio ad, many pharmaceutical companies have less incentive to inform consumers of useful information.

Dietary Supplement Health and Education Act of 1994 (DSHEA)

The DSHEA rejected the FDA’s attempt to regulate vitamins, minerals, oils, fibers, and other dietary supplements as drugs. Under the DSHEA, manufacturers can make statements of nutritional support but not drug claims. Manufacturer’s of St. John’s Wort, for example, may claim that St. John’s Wort “promotes healthy emotional balance and well-being,” but they cannot say St. John’s Wort “is useful in the treatment of depression.” The distinction is mostly one for lawyers, not consumers, considering that many consumers do take St. John’s Wort for depression. (Such consumers are in fact justified in doing so: a number of studies indicate that not only is St. John’s Wort effective at relieving mild cases of depression (e.g., Woelk 2000), but does so with fewer side effects than many antidepressive pharmaceuticals. In addition, St. John’s Wort is considerably cheaper than pharmaceuticals and does not require a prescription.) As another example, a manufacturer of cranberry juice might claim that “cranberry juice helps to maintain a healthy urinary tract” but could not maintain that cranberry juice is “useful in preventing a urinary tract infection (UTI)” despite the fact that millions of women do drink cranberry juice for that reason (although there is some scientific evidence that cranberry juice can prevent UTIs, it is, as of 2001, very preliminary).

The DSHEA also allowed manufacturers and retailers of dietary supplements to disseminate scientific information on the value and use of supplements.

More information can be found in the History section. The full text of the DSHEA can be found here. Pinco and Rubin (1996) offer a useful review of the legislation.

Drug Efficacy Study Implementation

The 1962 amendments authorized the FDA to test old as well as new drugs for efficacy. The FDA lacked the personnel to do these tests, so the National Academy of Sciences appointed a special committee to perform efficacy investigations on some four thousand pharmaceuticals. The committee, the Drug Efficacy Study Implementation (DESI), was composed of 160 physicians, who relied on their pharmacological knowledge, literature reviews, clinical experience, and intuition. The appointment of this group was somewhat paradoxical: instead of drawing on the knowledge of all doctors, which included knowledge about specific patients and what treatments had and had not worked on those patients, 160 doctors were empowered to decide for the nation in the absence of much relevant information.

Drug Lag and Drug Loss

Europe’s more efficient regulatory structure typically allows new drugs to be approved sooner in Europe than in the United States. The difference between the date of European adoption and that of U.S. adoption is known as drug lag. Drug lag has been important in the debate about the FDA because it is measurable and because U.S. legislators do not like to think that Europe does things better than the United States. Drug lag, however, is far from an ideal measure of the costs of the FDA. Note that drug lag will be reduced the more inefficient the European system becomes, but this is scant comfort for patients in the United States who die from lack of access to new drugs. Moreover, it is far from obvious that Europe has the best system of drug approval, even if it is faster than the system in the United States. More generally, as a result of the FDA’s long review times and extensive regulations, new drugs take longer to reach the marketplace than they would in a voluntary certification system. Because a voluntary certification system doesn’t presently exist, we cannot measure drug lag with respect to such a system, but such lag is almost certainly considerably longer than drug lag with respect to Europe.

The FDA does more than delay the introduction of new drugs; it also reduces the total number of new drugs created. This is known as drug loss. Drug loss is difficult to measure, although Peltzman’s (1973) results (see also the discussion in the text) suggest that it is very extensive.

Durham-Humphrey Amendment

The Durham-Humphrey Amendment codified the distinction between prescription and OTC drugs. A drug was to be an OTC drug unless (1) it was habit forming, (2) had potentially harmful effects or potentially harmful effects when used by a lay person, or (3) was limited to prescription use by a New Drug Application. Prior to this amendment, manufacturers decided whether a drug was to be sold OTC or by prescription only, but the company could be sued for misbranding if the FDA believed that the drug could not be properly labeled for consumer use.

More information on this amendment can be found in the History section.

Elixir Sulfanilamide

Elixir Sulfanilamide is a sulfa drug (antibiotic) released by Massengil in1937 in liquid form without prior toxicity testing of its solvent. The solvent diethylene glycol, used today as automotive antifreeze, caused the death of 107 people, mostly children. The chemist who created the elixir committed suicide. The “Elixir Sulfanilamide tragedy” prompted the passage of the Food, Drug, and Cosmetic Act of 1938. Although the deaths of 107 people were tragic, many more people have died because of FDA regulation. Deaths caused by drugs are seen, however, whereas deaths caused by a lack of drugs are unseen.

Ethical Drugs

The old term ethical drugs signified drugs advertised only to doctors. The expression refers to the original 1847 code of ethics of the AMA, which deemed advertising directly to the public to be unethical. Over time, the term came to mean legal drugs.

FDA Modernization Act of 1997

The 1997 Modernization Act moved in the direction of “reform”; thus, most of its requirements were in the direction of reducing FDA bureaucracy and speeding drugs and devices to patients. The act was, however, at best a modest reform package. Specifically, the Modernization Act reauthorized user fees for another five years, codified rules for fast-track approval, codified the rule that only one adequate and well-controlled clinical study and confirmatory evidence could be the basis of approval, and codified restrictive FDA policies on dissemination of information regarding off-label uses of drugs. (Washington Legal Foundation v. Friedman found such restrictions unconstitutional and further opened up the ability of firms to disseminate off-label information.) Concerning medical devices, the Modernization Act exempted most Class I and some Class II devices from premarket approval, and it increased physician authority to use investigational devices. Finally, in a variety of clauses, the FDA was required to provide manufacturers with better and more timely information concerning its procedures.

More information is available in the History section. The bill can be found online here.

Federal Trade Commission (FTC)

Set up in 1915 to restrain monopoly, the FTC monitored drug advertising from its inception until 1962, when the regulation of advertising of prescription drugs matter was transferred to the FDA. The FTC still regulates the advertising of OTC drugs, with a few exceptions, notably aspirin. On food products, the FDA and the FTC have split responsibilities, with the FDA regulating food labeling and the FTC regulating food advertising.

Form 510(k)

Manufacturers of a new medical device need not file a premarket approval form if the device is “substantially similar” to an already approved device that did not require a premarket approval form. Instead manufacturers may file the simpler form 510(k). The 510(k) was supposed to be a premarket notification that did not require approval. In the years following 1976, the FDA began to require that more and more information be included with the 510(k) notification. Now the industry considers the 510(k) to be the first in a series of premarket approval hurdles, rather than a notification. With the passage of the SMDA in 1990, the 510(k) officially became a premarket approval regulation.

Food, Drug, and Cosmetic Act of 1938

Passed after the Elixir Sulfanilamide tragedy, the Food, Drug, and Cosmetic Act required pharmaceutical manufacturers to submit a New Drug Application to prove the drugs’ safety. The act also provided the basis for the distinction between prescription and nonprescription drugs that was further developed in the Durham-Humphrey Amendment.

Generic Drugs

After a drug goes off-patent, any manufacturer who finds it profitable may produce an equivalent drug and sell it under the drug’s chemical or “generic” name. The original version is then called the brand-name drug, and the new competitive versions generic drugs. The Waxman-Hatch Act made it much easier for generic drugs to compete against their originals.

Good Manufacturing, Laboratory, and Clinical Practices (GMP, GLP, and GCP)

The various Good Practices are lengthy FDA rules and regulations governing manufacturing, laboratory, and clinical facilities. Most of the rules are obvious and include such things as, “Adequate washing facilities shall be provided, including hot and cold water, soap or detergent, air driers or single-service towels, and clean toilet facilities easily accessible to working areas,” and “Personnel shall practice good sanitation and health habits.” Many rules require the keeping of extensive written records. The current GMPs can be found here. Although the rules and accompanying inspections are not without utility, manufacturers rarely challenge the FDA, in part because they fear retaliation through arbitrary and capricious interpretation of the various standards and regulations (see, for example, the cases discussed by Volokh 1995).

The private sector also offers quality-control certification through such services as ISO 9000 Certification. The ISO 9000 standards are a series of standards for quality management that are produced by the Swiss organization International Organization for Standardization. The standards involve repeated audits and inspections.

Institutional Review Board (IRB)

IRBs review, approve, and monitor research involving human subjects in order to evaluate the ethical acceptability and the scientific validity of any such studies. An IRB is formally designated by an institution in which research takes places, such as a hospital or university. FDA regulations on IRB membership are quite strict. The IRB must be composed of at least five members including at least one scientific member, one nonscientific member, at least one person not affiliated with the research institution, no members with conflicts of interests, both genders if at all possible, and so forth. Research cannot begin until the IRB approves.

Investigational Device Exemption (IDE)

Medical devices must receive FDA approval before being marketed (since the 1976 Medical Device Amendments to the Food, Drug, and Cosmetic Act). Similar to an IND, an IDE allows companies to sell and use a limited number of devices for investigation purposes and clinical trials. The IDE exempts the device not only from the premarket approval regulation but also from a host of other reporting and recording regulations.

Investigational New Drug Application (IND)

Before testing a new drug on human subjects, the company must file an IND. Prior to filing an IND, the sponsor develops information on the chemistry of the drug so that it can be produced in batches of known strength and purity. In addition, the sponsor must conduct a number of animal studies to produce information on the pharmacology and toxicology of the drug. Information, for example, must be produced on the absorption, distribution, metabolism, and excretion properties of the drug. Finally, detailed protocols for testing on human subjects must be submitted. In addition, since 1971, the FDA has required that all proposed clinical studies be reviewed by an institutional review board. Technically, unless otherwise notified, the sponsor can begin clinical studies within thirty days (if the IRB approves). The FDA can, however, terminate an IND at any time; thus in practice the FDA must approve the IND proposal. The IND stage of drug approval is broken into three phases. The FDA exerts considerable control over all phases of the clinical trial process, and at any stage the FDA can and often does request additional clinical trials and changes in trial protocols.

Phase I
This phase consists of short-term clinical tests of the drug on twenty to eighty healthy volunteers to determine basic pharmacological and toxicological information in humans especially as regards safety. The FDA can stop clinical testing if they deem the drug unsafe.

Phase II
This phase consists of small-scale, longer-term tests for efficacy and safety. Typically the drug is tested in one hundred to three hundred patients. In phase II trials, dosage levels are experimented with to find optimal dosage levels, and further information on safety is collected.

Phase III
Large-scale testing for safety and effectiveness is conducted in phase III. Typically one thousand to three thousand patient volunteers are used in this phase. The primary information the FDA will use to decide whether the drug satisfies its (often arbitrary) benefit-risk relationship is developed in phase III trials. The trials are tightly controlled, may involve a large number of patients, and can take several months to several years for completion.

The Jungle

Upton Sinclair’s famous muckraking novel about the Chicago meatpacking industry contained outlandish, graphic images of Durham’s Pure Leaf Lard being made out of the remains of workmen who had fallen into the cooking vats. (See Libecap and Pasour for critical examinations of the issues raised in this book.) When this 1906 novel upset the public, regulation advocates used the public’s reaction to secure passage of the Pure Food and Drug Act of 1906 (as well as the Meat Inspection Act of 1906).

Kefauver-Harris Bill of 1962

Also known as the 1962 Amendments to the Food, Drug, and Cosmetic Act of 1938, the Kefauver-Harris bill required pharmaceutical firms to wait for FDA approval prior to marketing their product. By law, the FDA is supposed to review an NDA within 180 days, but no penalties for failure exist, and the FDA has never come close to meeting this requirement. Additionally, the 1962 Amendments required the firm to show that a drug is efficacious in addition to safe for all labeled uses. The 1962 Amendments also brought clinical research and development under the authority of the FDA. Drug sponsors henceforth had to file an Investigational New Drug Application and obtain FDA approval for all investigational studies involving humans. Laboratories and clinics engaged in research also became subject to Good Laboratory Practice and Good Clinical Practice regulations that required extensive paperwork.

More information can be found in the History section.

Knower Organization

An organization that knows more than the consumer about a seller’s reputation or about the quality and safety of the seller’s products is called a knower organization. The term usually refers to private, voluntary organizations. Knower organizations, when paid by the seller, often inspect quality and safety, and grant a seal of approval or certification mark, just as Underwriters’ Laboratories does for electronic safety, Orthodox Union does for kosher foods, Moody’s does for securities, medical schools do for newly graduated practitioners, and the American Dental Association does for dental products. Alternatively, knower organizations may investigate quality and safety, and sell their reports directly to consumers, as do Consumer Reports, credit bureaus, and doctors and pharmacists who recommend which drugs to take. Medical groups, hospital affiliations, and medical degrees are types of seals of approval that assure consumers that they can trust the doctor who recommends a drug. In the drug field, the growth and development of knowers and knower organizations are severely stunted by FDA command of the drug and device industries. Nonetheless, such organizations would surely expand and mature if people were freer in making their own drug choices.

Medical Device Amendments of 1976

These amendments greatly increased the FDA’s control over medical devices. The amendments divided medical devices into three classes. Class I devices are subject to general control requirements (certain records and reports provided to the FDA by the manufacturer); Class II devices are subject to general control and specific performance-based standards; and Class III devices are subject to a premarket approval process that is much like the approval process for new drugs. In addition, the amendments gave the FDA power to ban medical devices, to require manufacturers to inform consumers of potential hazards, and to force manufacturers to give refunds.

See the History section for more information.

Medical Device Reports

This law requires hospitals, ambulance services, surgical facilities, nursing homes, and outpatient facilities to file a report to the FDA if a device is “associated with” any death, injury, or illness. With respect to sick individuals, however, it’s often difficult to say whether a device is “associated with” an adverse event in any meaningful way. Medical device reports have thus involved extensive paperwork, a large fraction of which the FDA never reads (Higgs 1995c). Adverse events reports involving devices and patient death must be sent directly to the FDA, whereas reports of events that have caused injury or illness are sent to the manufacturer.


A retail drug store or pharmacy is an example of a middleman. The middleman purchases goods from suppliers and then sells to consumers. Middlemen are very important in providing assurance of quality and safety because they have repeated dealings with customers and wish to induce the customer to continue buying from them. A pharmacy that sold someone an unsafe drug not only would be subject to suit, but would probably lose that person’s business and perhaps the business of those who learned of the mishap. Seeking to build and preserve a good reputation, pharmacies have a strong incentive to exclude unsafe or ineffective drugs from their shelves. They have strong incentives to know which drugs are safe and which dangerous. Another form of middleman is the pharmaceutical company. The company purchases the inventions and discoveries of researchers, develops them into brand-name products, and then sells them to the public. To preserve the reputation of the brand name and to avoid lawsuits, the company thinks carefully before putting a new drug on the market. Another example of a middleman is a hospital or clinic that purchases supplies and equipment, and employs staff. Consumers have repeat dealings with the hospital, and the hospital has repeat dealings with its suppliers and staff; in this way, the middleman creates a bridge of reputation and trust from consumers to the suppliers and the staff.

National Formulary

Published by the U.S. Pharmacopoeia (USP), a private nonprofit organization, the National Formulary is the official compendium of standards for drugs, excipients, dietary supplements, and vitamins and minerals. The USPNF defines standards of strength, quality, purity, identity, packaging, labeling, and storage, and describes and defines the appropriate tests, assays, and analytical methods that are used to measure strength, purity, and so forth. The USP also publishes the USPDI, a compendium of drug information that is also officially recognized in the United States and in many other countries worldwide.

New Chemical Entities

In the early stages of research, a new substance is called a new chemical entity, a chemical entity that has never been used by humans and has been tested only on animals.

New Drug Application (NDA)

Under the Food, Drug, and Cosmetic Act of 1938, the NDA was submitted to the FDA enumerating the uses of the drug and providing evidence of its safety. If the FDA found no reason to object, the NDA was automatically approved within sixty days. But since 1962 the FDA evaluates proof of efficacy as well as proof of safety, and the company must wait for FDA approval no matter how long that takes. On average, the NDA review process lasts for two years (as of the mid-1990s, some evidence suggests times have shortened). The NDA review is handled by the FDA’s Center for Drug Evaluation and Research (CDER). Once the CDER deems the NDA fileable, the medical, biopharmaceutical, pharmacology, statistical, chemistry, and microbiology departments of the CDER review it. The length of an NDA application can reach one hundred thousand pages of material. If the departments pass the NDA, an advisory committee meets. If the advisory committee is satisfied with all of the findings, a labeling review takes place. Once the labeling review is complete, the NDA is approved, and the drug is ready to be marketed.

Nutrition Labeling and Education Act (NLEA)

The NLEA required food manufacturers to include nutritional labeling on most food products. The NLEA also codified the FDA’s authority to allow health claims on foods and dietary supplements. Although the intent of the NLEA was to increase the amount of information consumers received by broadening the health claims allowed on foods and dietary supplements, the FDA officials took an aggressive stance and announced that they planned to regulate supplements as drugs. The resulting backlash led to the passing of the Dietary Supplement Health and Education Act (DSHEA) of 1994.

On-Label Uses and Off-Label Uses

Many drugs that have gained FDA approval have uses other than those for which the drug was officially evaluated and approved. Once a drug has been approved for some use, however, it can be legally prescribed for any use. Approved uses are known as on-label uses, whereas other uses are off-label uses. Manufacturers may disseminate information, either in literature to doctors or in advertisements to the public, about on-label uses, subject to restrictions such as the brief summary. But disseminating information about off-label uses was prohibited between 1962 (the Kefauver Amendments) and 1997 (the Modernization Act). Off-label uses are often very important and common. Amoxicillin and tetracycline are today routinely used to treat stomach ulcers following Barry Marshall’s revolutionary discovery that ulcers are caused by Helicobacter pylori, but they are not approved for such uses (as of the late 1990s). Aspirin is also routinely used to prevent heart attack, even though it is not an approved use (as of 2000). Restriction on advertising and information dissemination have limited the information available to doctors and have thus sometimes prevented patients from receiving needed medication. Many of the FDA’s restrictions on dissemination of information related to off-label prescriptions were declared unconstitutional in Washington Legal Foundation v. Friedman D.D.C. See also the discussion in the text and Tabarrok (2000).

Orphan Drug Act (ODA) of 1983

The market for some drugs is small because the disease treated is rare or because only a small number of people do not respond satisfactorily to the existing therapies. Nevertheless, because there are many diseases that affect only a small number of people, the total number of Americans with an orphan disease has been estimated to be twenty to thirty million (Meyers 1991). Because the costs of getting through the FDA process are the same whether the intended market for the drug is fifty thousand patients or five million patients, drug loss has been especially prevalent for orphan diseases. The 1983 Orphan Drug Act, amended in 1984, recognized this problem, but rather than reducing review times or directly lowering the burden of FDA-required trials, it created more government programs to try to counter the effect of the FDA. In particular, the ODA provided for grants to defray the costs of testing products for rare diseases and gave sponsors of orphan products tax credits on their development costs. Most importantly, the FDA agreed that once it approved one sponsor’s drug, it would not approve any other similar drug for the same indication for a period of seven years. In effect, sponsors were given monopoly rights. Thus, the number of drugs for orphan indications was increased but at the cost of higher-priced drugs. A notable example of how the ODA has been abused is that the AIDS drug AZT was granted orphan status and has since earned many billions in sales revenue.

More information is available in the History section. See also Arno, Bonuck, and Davis (1995).

Over-the-Counter Drug

A drug that is available to the consumer without a prescription. As recently as 1940, all nonnarcotic drugs were available over the counter.

Parallel Tracking

Initially designed to help AIDS patients, parallel tracking makes drugs showing promising results in phase III of the IND process available to patients whose condition prevents them from participating in controlled clinical trials. Parallel tracking is similar to the treatment IND, a program started several years earlier.

Patent Medicine

Patent medicine is a term from the pre-1938 era signifying not that the drug was patented, but that it was advertised directly to the public and that its ingredients were not being fully disclosed. Patent medicines often contained alcohol, opiates, or cocaine, providing relief rather than cure.

Pearson v. Shalala

Pearson v. Shalala forced the FDA to relinquish some control over medical statements on dietary supplements. Congress authorized the FDA to pre-approve health claims on foods [in the Nutrition Labeling and Education Act (NLEA)] but the FDA created an undefined and apparently very difficult to pass standard for approving such health claims, and after 10 years had approved only 10 such claims (Steinborn and Todd 1999).

Durk Pearson and Sandy Shaw, supplement manufacturers, wanted to make four health claims on their dietary supplement labels. The proposed claims were “(1) Consumption of antioxidant vitamins may reduce the risk of certain kinds of cancers. (2) Consumption of fiber may reduce the risk of colorectal cancer. (3) Consumption of omega-3 fatty acids may reduce the risk of coronary heart disease. And (4) .8 mg of folic acid in a dietary supplement is more effective in reducing the risk of neural tube defects than a lower amount in foods in common form.”

Although there is scientific information supporting the claims and although such claims are widely heard in the mainstream health-media, the FDA refused to allow any of them. Pearson and Shaw sued in federal district court based on the First Amendment and the FDA’s failure to define their standard for accepting a health claim. After losing initially, the D.C. Court of Appeals ruled that dietary supplements may be labeled with medical claims as long as they bear a disclaimer that such claims have not received FDA approval.


A placebo is a pharmacologically inert capsule, injection, or procedure. The placebo effect is the improvement in well being that is due to medical attention coupled with the use of mere placebos.

The placebo effect must be distinguished from “regression to the mean,” the statistical likelihood that a sick person will get better absent any treatment. The placebo effect is best defined as the improvement in well being in a group treated with a placebo compared to a similar (ideally, randomly assigned) group that is not treated at all (Hróbjartsson and Gotzsche, 2001).

Though controversial, there is evidence that a significant placebo effect exists, especially when treating the symptoms of pain, stress, depression, and anxiety. Scientific evidence also supports the notion that a patient’s attitude and spirits affect her recovery. Brown and Severs provide a good description of how the placebo effect may be tied to such factors:

“A sense of control is restored when a patient decides to seek medical assistance. Furthermore, the symbols and rituals of healing—the doctor’s office, the stethoscope, a thorough physical examination, and a treatment prescription—offer reassurance. So, too, an explanation of the illness and the prognosis, when favorable, reduces fear and uncertainty . . . Plausible treatment mobilizes a patient’s hope and creates expectation of improvement” (Brown and Severs 1999, 33).

Brown and Severs provide a sample statement that a doctor might make to a patient when prescribing a placebo found to improve health—a statement that is truthful and nonmisleading yet might accommodate an improvement in attitude and spirits.

FDA efficacy requirements demand that a drug be proven “effective beyond a placebo.” Sobel (2002) argues that this standard unnecessarily reduces the development of and public access to placebos that would alleviate suffering.

Poison Squad

Early in the twentieth century, Harvey Wiley, chief of the Bureau of Chemistry, was intent on showing the dangers of an uncontrolled food industry. He recruited a volunteer group of young men and had them ingest large quantities of foods with additives and preservatives, such as formaldehyde and boric acid. The consequent ailments of the Poison Squad (1902–6) were well publicized and helped to pave the way for the Pure Food and Drugs Act of 1906.

Preclinical Research

The first stage in drug development, preclinical research, involves synthesis and purification testing in the lab and animal testing. Thousands of compounds are tested in preclinical research before a handful are chosen to enter the second stage, which requires filing of an IND.

Premarket Approval

Premarket approval means that regulators must authorize a product, process, batch, or facility before it is allowed to serve the market. That which is not specifically permitted is forbidden. Aaron Wildavsky (1988) has distinguished the hubristic anticipatory approach of premarket approval from the humble resilience approach of the freedom of contract plus postmarket inspection and recourse (through tort, legal, or recall procedures). Wildavsky argues that the resilience approach allows for flexibility, differentiation, experimentation, and entrepreneurship. Beginning with the 1902 Biologics Act, however, government control has consistently enacted the anticipation approach by expanding premarket approval requirements. Today, drugs and medical devices must obtain premarket approval by the FDA before the product is allowed on the market. Devices categorized as Class III require premarket approval. According to the 1976 Amendments, all new devices were automatically placed in Class III even if they were low-risk devices. Since the FDA Modernization Act of 1997, new low-risk devices can go through an abbreviated process.

Prescription Drugs

Drugs that consumers may purchase only if they have a doctor’s prescription, in contrast to OTC drugs, are called prescription drugs. Prescription requirements induce consumers to call on doctors; hence, they raise doctors’ income. Prescription requirements may also be viewed in relation to drug prohibition. Prescription laws give doctors the privilege of authorizing the sale of FDA-approved narcotics that are substitutes for illegal “recreational” drugs. To prevent doctors from becoming authorized “drug dealers,” the DEA and other authorities monitor and enforce against doctors who “overprescribe” narcotics (known as “script doctors”).

See also the subsection Prescription-Only Requirements.

Prescription Drug User Fee Act of 1992 (PDUFA)

Traditionally, the FDA, like other bureaucracies, obtained its funding from general tax revenues according to congressional appropriations. In addition to having biased incentives, the FDA has at times been slow to approve new drugs because it lacked adequate resources to hire enough competent investigators to examine NDAs. Thus, many people died as NDAs sat unexamined on reviewers’ desks. In 1992, Congress authorized the FDA to charge drug companies a user fee. The term fee is dubious because fee usually means payment for services rendered, but is it appropriate to call the FDA’s deliberation over whether to grant permission a “service”? The “user fee” is rather like ransom received for “the service” of releasing a kidnapped child.

In 2006 the FDA collected over $300 million in so-called user fees, which constituted 58 percent of its total drug and biological review funding (with the rest coming from FDA appropriations). The FDA must report these figures every year in a PDUFA financial report; the link is to the 2006 report. Initially authorized for five years, the fee act was extended for another five years in the FDA Modernization Act of 1997. Subsequently PDUFA III and PDUFA IV followed in five-year intervals.

User fees have reduced the FDA’s average review times and increased access to new drugs (Philipson et al. 2005 and Berndt et al. 2005) but total time to bring a drug to market was not changed appreciably because of increases in the clinical development time (GAO 2002, Kaitin and DiMasi 2000). The FDA must provide performance figures once a year in a PDUFA performance report; the link is to the 2006 report.

More information is available in the History section.

Proof of Efficacy

Part of the 1962 Amendments, the proof-of-efficacy standard requires firms to produce evidence demonstrating that their product is efficacious for claimed uses. The proof-of-efficacy standard creates the distinction between on-label and off-label uses. The FDA reasons that because off-label uses have not passed proof of efficacy, the company is banned from disseminating information about such uses.

Pure Food and Drugs Act of 1906

This act banned the adulteration and mislabeling of food and drugs. It required that products specify the quantity of certain substances (alcohol, morphine, opium, cocaine, heroin, alpha- or beta-eucaine, chloroform, cannabis indicia, chloral hydrate, and acetanilide). It declared the U.S. Pharmacopoeia and the National Formulary to be the official documents determining standards. If a drug differed from these standards, the difference had to be stated on the package. The act did not address advertisements. Regarding therapeutic claims for a drug, in 1911 the Supreme Court ruled that the act did not prohibit claims that were false but not fraudulent. Along similar lines, the Sherley Amendment of 1912 decisively banned fraudulent claims. In other words, drug sellers could make therapeutic claims, even false claims, as long as they could plausibly show that they believed their own claims.

Rare Diseases

Rare diseases, as defined by the Orphan Drug Act, are those diseases or conditions affecting less than two hundred thousand persons in the United States at the time of designation. Or they may be diseases or conditions that affect more than two hundred thousand persons but for which the costs of developing a drug cannot be recouped within seven years from sales in the United States.


If the United States and, say, Britain had drug approval reciprocity, then drugs approved in Britain would automatically and immediately gain approval in the United States as well. The logic of such a proposal suggests that the U.S. government ought to establish reciprocity with countries that have a proven record of approving safe drugs. Such an arrangement would eliminate the delay with which drugs approved abroad become available to Americans. The FDA opposes the proposal, presumably because the reform would introduce competition. American drug companies would apply to, say, the British authority for approval because it is more efficient and reasonable in reviewing applications.


In any industry, trade, or profession, a seller‘s trading partners, associates, and customers develop opinions of his trustworthiness. They develop a sense of whether the seller’s products and services live up to the quality and safety that he promises. A good reputation is one of the most important keys to success because a good reputation will bring satisfied customers calling again and will bring others who hear of the seller’s good reputation. If the seller sells an unsafe product, he not only will pay tort penalties, but will lose reputation and business. Reputation is generated by word of mouth and by other informal means, but also by various knower organizations that evaluate, rate, and report on the seller’s quality and safety.

Safe Medical Devices Act of 1990 (SMDA)

Passed in 1990, the SMDA has greatly broadened FDA authority over the medical devices industry. The act requires Medical Device Reports; not filing the reports can result in fines. The SMDA also formally changed the 510(k) procedure, which was originally intended to be a notification procedure, to a premarket approval procedure. The SMDA also permitted the assessment of substantial civil penalties for violating the Food, Drug, and Cosmetic Act relating to devices.

More information is available in the History section.

Seal of Approval

When a knower organization evaluates a product or service, it often grants a seal of approval such as a certification mark, a degree, or a rating, which helps to determine the seller’s reputation and provides assurance to consumers.

Sherley Amendment of 1912

See Pure Food and Drugs Act of 1906.

Sinclair, Upton

Socialist novelist and muckraker who wrote The Jungle in 1906. See Libecap and Pasour for critical examinations of the issues raised in this book.

Split-Label Proposal

The split-label proposal is a reform proposal that would reduce the FDA suppression of information. The product label would consist of a part for FDA-approved health and nutrition claims and a part for non-FDA-approved claims. (A larger stride toward medical freedom would be to permit the marketing of products not approved by the FDA, provided that the label clearly indicates that the product is not FDA approved.) Although retaining FDA certification for those who want assurance from the FDA, the split-label approach would increase the amount of information available to the consumer and evoke market mechanisms, such as knowers and middlemen, to provide nongovernmental assurance of quality and safety.
Supplemental New Drug Application (SNDA)

The off-label uses of a drug may become additional on-label uses if the company submits a Supplemental New Drug Application and the FDA approves the application. SNDAs may take years to process and can be expensive. When a drug is off-patent or if the off-label use is for only a small population, there is little incentive (except that it is easier to advertise on-label uses) for a firm to obtain an SNDA.

Surrogate Endpoints and Postmarketing Studies

It’s often very expensive or time-consuming to measure the effect of a drug on an ultimate goal such as mortality. Drugs to reduce cholesterol, for example, are intended ultimately to reduce the number of heart attacks and thus to lengthen life expectancy. It could take twenty or more years to test this hypothesis adequately, however. A surrogate endpoint, such as a reduction in cholesterol counts, is a more easily measured endpoint. A drug may be approved based on clinical trials showing a positive surrogate endpoint if there is evidence from other studies that the surrogate endpoint accurately predicts an ultimate benefit. (We know, for example, that men with high cholesterol are at greater risk of a heart attack, but this is not the same as knowing that a reduction in cholesterol will reduce heart attacks, although it is suggestive.) Postmarketing studies can continue to track the effectiveness of drugs that were approved using surrogate endpoint methodology.

The use of surrogate endpoints is controversial because a positive surrogate endpoint does not necessarily predict a positive ultimate endpoint. Encainide and flecainide were widely prescribed because they prevented premature beats of the heart on the theory that such prevention would reduce heart attacks. The Cardiac Arryhythmia Suppression Trial later showed that not only was this claim false but that encainide and flecainide could actually increase the number of heart attacks. See Moore (1995) and the brief discussion in Tabarrok (2000).


The sedative thalidomide was released in Europe in 1957 and taken by pregnant women to relieve morning sickness. Tragically, the drug caused severe birth defects in more than ten thousand children. When the horrible side effects were discovered, the drug was still pending approval by the FDA, which held up the drug for reasons unrelated to its danger to fetuses. Hence, the old, pre-1962 FDA was adequate in screening out thalidomide. Nonetheless, supporters of FDA power used the thalidomide tragedy to secure the 1962 Amendments, which vastly enhanced FDA power. Since that time, thalidomide has been a terrifying word. Yet as early as 1965 the drug was discovered to be effective in treating leprosy and in places other than the United States has long been the standard treatment for that disease. Thalidomide has also been used to treat other diseases, including lupus, some cancers, and Kaposi’s sarcoma. Yet only in 1998 did the FDA finally permit Americans to use thalidomide. Special rules require that doctors and their patients register with the drug manufacturer and the FDA before thalidomide can be prescribed; women who take the drug must agree to use two forms of contraception and to submit to biweekly pregnancy tests.

Treatment IND

This application allows drugs that are at the end of phase III clinical testing to be made available to patients who are suffering from a serious or immediately life-threatening condition when there is no other treatment available. An “immediately life-threatening” condition is defined as one that will result in death within a few months. Instituted in the late 1980s in response to the AIDS crisis, this practice is similar in effect to parallel tracking.

Types of Error in FDA Decisions

Even after extensive testing, the safety and effectiveness of a new drug are always somewhat uncertain. The FDA can thus never be certain that a new drug, device, use, or claim will be a net good or a net bad for society. Type 1 errors occur when the FDA approves a drug that ends up being a net bad for society. Type 2 errors occur when the FDA rejects a drug that would be a net good for society. Type 1 errors produce identifiable victims. Such errors are very visible and often result in major media attention, public concern, and congressional action against the FDA. Hence, the FDA has a strong incentive to avoid type 1 errors. The FDA makes sure that type 1 errors are rare by increasing the length of the drug approval process and by requiring more extensive clinical trials. Such overcaution is deadly, however, because it leads to more type 2 errors: not permitting a drug, device, use, or claim that would be a net good to society. Type 2 errors are less visible because patients, doctors, and journalists are usually unaware that a drug has been delayed or suppressed and that it would have saved individuals. The victims of type 2 errors, the people who would have lived if the FDA had not delayed the legal use of a new drug, are just as real as those who die because the FDA approved a bad drug, but they are known only in a statistical sense and are much less salient. Intelligent drug policy should aim to minimize the harm associated with both types of error. Although AIDS and cancer patients have sometimes been vocal in protesting FDA drug suppression, for the most part there is no informed, organized constituency to represent those who suffer as the consequences of type 2 errors. Thus, instead of minimizing total harm, the FDA focuses excessively on avoiding type 1 errors, resulting in many type 2 victims, invisible to the public eye but no less real.

For further discussion, see FDA Incentives.

Underwriters Laboratories Inc. (UL)

Underwriters Laboratories Inc. (UL) is a private, not-for-profit, product safety testing and certification organization. Founded in 1894, UL tests more than eighteen thousand different products for more than fifty thousand customers. It operates testing centers and has customers throughout the world. On a voluntary basis, manufacturers submit products to UL for testing and safety certification. There are no laws specifying that a UL mark must be used. (In the United States, many municipalities have laws, codes, or regulations that require a product to be tested by a nationally recognized testing laboratory before it can be sold in the area, but not necessarily by UL, so UL does not have a monopoly.)

UL successfully ensures high-quality standards in the fields of electrical products, fire suppression devices, automotive equipment, and much more. UL even certifies the electrical and mechanical aspects of medical devices. The success of UL in these fields suggests that UL and similar organizations might also ensure safe and high-quality drugs (Campbell 1999).

U.S. Pharmacopoeia and USP-DI

Published by U.S. Pharmacopoeia (USP), a private nonprofit organization, the USP-DI is a compendium of drug uses, covering both on-label and off-label uses. Using panels of expert physicians who evaluate the literature and clinical practice, the USP-DI presents information on which drugs are recommended for which uses, warnings, contraindications, dosages, etc. To keep up with best practices, it is updated regularly. The USP-DI is the best known of several such compendia. The USP also publishes the National Formulary.

The Complete Drug Reference, published jointly with Consumer Reports, is the consumer version of the USP-DI. The Complete Drug Reference contains more information than the Physicians Desk Reference (PDR), which is useful but compiles product label information only and thus does not deal with off-label usages.

Washington Legal Foundation v. Friedman D.D.C. (July 20, 1998)

Prior to this ruling, the FDA had maintained that manufacturers could not disseminate information about off-label uses to physicians, even photocopies of peer-reviewed journal articles, except under strict conditions (mainly that the manufacturer had to be in the process of submitting an SNDA for the off-label use). In WLF v. Friedman, the court ruled that many of the FDA’s restrictions violated the commercial free-speech rights of manufacturers. The FDA’s policies had in the meantime been codified by Congress in Section 401 of the FDA Modernization Act of 1997 (which did not become effective until late 1998). This aspect of the 1997 statute was subsequently struck down as unconstitutional by the same district court. On appeal, in Washington Legal Foundation v. Henney 202 F.3d 331 (D.C. Cir. 2000), the FDA backed down from its earlier position and reinterpreted section 401 of the Modernization Act in a way consistent with the district court’s ruling in WLF v. Friedman. Hence, the court decisions have broadened manufacturers’ freedom to disseminate information about off-label uses, though such freedom remains restricted.

Waxman-Hatch Act (1984 Drug Price Competition and Patent Term Restoration Act)

The 1984 Drug Price Act extended patent terms to account for the time it took a drug to receive FDA approval, and it reduced the barriers to entry for generic drug producers by allowing them to assert safety and efficacy based on information in the original NDA and on a proof that the original drug and generic drug are bioequivalent. The submission procedure for a generic drug is called an Abbreviated New Drug Application (ANDA).

More information is available in the History section.

Part 2: 

Drugs@FDA Glossary of Terms

 Abbreviated New Drug Application (ANDA) 

An Abbreviated New Drug Application (ANDA) contains data that, when submitted to FDA's Center for Drug Evaluation and Research, Office of Generic Drugs, provides for the review and ultimate approval of a generic drug product. Generic drug applications are called "abbreviated" because they are generally not required to include preclinical (animal) and clinical (human) data to establish safety and effectiveness.  Instead, a generic applicant must scientifically demonstrate that its product is bioequivalent (i.e., performs in the same manner as the innovator drug). Once approved, an applicant may manufacture and market the generic drug product to provide a safe, effective, low cost alternative to the American public.

Abbreviated New Drug Application (ANDA) Number 

This six-digit number is assigned by FDA staff to each application for approval to market a generic drug in the United States.

Active Ingredient 

An active ingredient is any component that provides pharmacological activity or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease, or to affect the structure or any function of the body of man or animals.

Approval History 

The approval history is a chronological list of all FDA actions involving one drug product having a particular FDA Application number (NDA).  There are over 50 kinds of approval actions including changes in the labeling, a new route of administration, and a new patient population for a drug product.


See New Drug Application (NDA),  Abbreviated New Drug Application ANDA), or Biologic License Application (BLA)

Approval Letter 

An official communication from FDA to a new drug application (NDA) sponsor that allows the commercial marketing of the product.

Application Number 

See FDA Application Number

 Biologic License Application (BLA)

Biological products are approved for marketing under the provisions of the Public Health Service (PHS) Act. The Act requires a firm who manufactures a biologic for sale in interstate commerce to hold a license for the product. A biologics license application is a submission that contains specific information on the manufacturing processes, chemistry, pharmacology, clinical pharmacology and the medical affects of the biologic product. If the information provided meets FDA requirements, the application is approved and a license is issued allowing the firm to market the product.

Biological Product

Biological products include a wide range of products such as vaccines, blood and blood components, allergenics, somatic cells, gene therapy, tissues, and recombinant therapeutic proteins. Biologics can be composed of sugars, proteins, or nucleic acids or complex combinations of these substances, or may be living entities such as cells and tissues. Biologics are isolated from a variety of natural sources — human, animal, or microorganism — and may be produced by biotechnology methods and other cutting-edge technologies. Gene-based and cellular biologics, for example, often are at the forefront of biomedical research, and may be used to treat a variety of medical conditions for which no other treatments are available.

In general, the term "drugs" includes therapeutic biological products.

Brand Name Drug

A brand name drug is a drug marketed under a proprietary, trademark-protected name.

Chemical Type

The Chemical Type represents the newness of a drug formulation or a new indication for an existing drug formulation.  For example, Chemical Type 1 is assigned to an active ingredient that has never before been marketed in the United States in any form.  (list of Chemical Types and their meanings)


The company (also called applicant or sponsor) submits an application to FDA for approval to market a drug product in the United States.

 Discontinued Drug Product  

Products listed in Drugs@FDA as "discontinued" are approved products that have never been marketed, have been discontinued from marketing, are for military use, are for export only, or have had their approvals withdrawn for reasons other than safety or efficacy after being discontinued from marketing.

Dosage Form 

A dosage form is the physical form in which a drug is produced and dispensed, such as a tablet, a capsule, or an injectable.


A drug is defined as:

  • A substance recognized by an official pharmacopoeia or formulary.

  • A substance intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease.

  • A substance (other than food) intended to affect the structure or any function of the body.

  • A substance intended for use as a component of a medicine but not a device or a component, part or accessory of a device.

  • Biological products are included within this definition and are generally covered by the same laws and regulations, but differences exist regarding their manufacturing processes (chemical process versus biological process.) 

Drug Product  

The finished dosage form that contains a drug substance, generally, but not necessarily in association with other active or inactive ingredients.

 FDA Action Date  

The action date tells when an FDA regulatory action, such as an original or supplemental approval, took place.

FDA Application Number  

This number, also known as the NDA (New Drug Application) number, is assigned by FDA staff to each application for approval to market a new drug in the United States. One drug can have more than one application number if it has different dosage forms or routes of administration

 Generic Drug

A generic drug is the same as a brand name drug in dosage, safety, strength, how it is taken, quality, performance, and intended use. Before approving a generic drug product, FDA requires many rigorous tests and procedures to assure that the generic drug can be substituted for the brand name drug. The FDA bases evaluations of substitutability, or "therapeutic equivalence," of generic drugs on scientific evaluations. By law, a generic drug product must contain the identical amounts of the same active ingredient(s) as the brand name product. Drug products evaluated as "therapeutically equivalent" can be expected to have equal effect and no difference when substituted for the brand name product.


The FDA approved label is the official description of a drug product which includes indication (what the drug is used for); who should take it; adverse events (side effects); instructions for uses in pregnancy, children, and other populations; and safety information for the patient.  Labels are often found inside drug product packaging.

 Marketing Status  

Marketing status indicates how a drug product is sold in the United States.   Drug products in Drugs@FDA are identified as:

  • Prescription

  • Over-the-counter

  • Discontinued

  • None - drug products that have been tentatively approved 

Medication Guide  

A medication guide contains information for patients on how to safely use a drug product.

 NDA (see  New Drug Application)

New Drug Application (NDA) 

When the sponsor of a new drug believes that enough evidence on the drug's safety and effectiveness has been obtained to meet FDA's requirements for marketing approval, the sponsor submits to FDA a new drug application (NDA). The application must contain data from specific technical viewpoints for review, including chemistry, pharmacology, medical, biopharmaceutics, and statistics. If the NDA is approved, the product may be marketed in the United States.  For internal tracking purposes, all NDA's are assigned an NDA number.

New Drug Application (NDA) Number 

This six digit number is assigned by FDA staff to each application for approval to market a new  drug in the United States. A drug can have more than one application number if it has different dosage forms or routes of administration. In Drugs@FDA, you can find the NDA number under the column named "FDA Application."

NME (see New Molecular Entity)

New Molecular Entity (NME)  

A New Molecular Entity is an active ingredient that has never before been marketed in the United States in any form.  Over-the-Counter Drugs (OTC)  

FDA defines OTC drugs as safe and effective for use by the general public without a doctor's prescription.

 Patient Package Insert (PPI)  

A patient package insert contains information for patients' understanding of how to safely use a drug product.

Pharmaceutical Equivalents

FDA considers drug products to be pharmaceutical equivalents if they meet these three criteria:

  • they contain the same active ingredient(s)

  • they are of the same dosage form and route of administration

  • they are identical in strength or concentration 

Pharmaceutically equivalent drug products may differ in characteristics such as

  • shape

  • release mechanism

  • labeling (to some extent)

  • scoring

  • excipients (including colors, flavors, preservatives) 

Prescription Drug Product

A prescription drug product requires a doctor's authorization to purchase.

Product Number  

A product number is assigned to each drug product associated with an NDA (New Drug Application).  If a drug product is available in multiple strengths, there are multiple product numbers.

 Reference Listed Drug (see RLD)


A review is the basis of FDA's decision to approve an application.  It is a comprehensive analysis of clinical trial data and other information prepared by FDA drug application reviewers.  A review is divided into sections on medical analysis, chemistry, clinical pharmacology, biopharmaceutics, pharmacology, statistics, and microbiology.

Review Classification

The NDA and BLA classification system provides a way of describing drug applications upon initial receipt and throughout the review process and prioritizing their review. (List of Review Classifications and their meanings)

RLD (Reference Listed Drug) 

A Reference Listed Drug (RLD) is an approved drug product to which new generic versions are compared to show that they are bioequivalent. A drug company seeking approval to market a generic equivalent must refer to the Reference Listed Drug in its Abbreviated New Drug Application (ANDA).  By designating a single reference listed drug as the standard to which all generic versions must be shown to be bioequivalent, FDA hopes to avoid possible significant variations among generic drugs and their brand name counterpart.


A route of administration is a way of administering a drug to a site in a patient. A comprehensive list of specific routes of administration appears in the CDER Data Standards Manual.


The strength of a drug product tells how much of the active ingredient is present in each dosage.


A supplement is an application to allow a company to make changes in a product that already has an approved new drug application (NDA). CDER must approve all important NDA changes (in packaging or ingredients, for instance) to ensure the conditions originally set for the product are still met.

Supplement Number 

A supplement number is associated with an existing FDA New Drug Application (NDA) number. Companies are allowed to make changes to drugs or their labels after they have been approved.  To change a label, market a new dosage or strength of a drug, or change the way it manufactures a drug, a company must submit a supplemental new drug application (sNDA).  Each sNDA is assigned a number which is usually, but not always, sequential, starting with 001.

Supplement Type 

Companies are allowed to make changes to drugs or their labels after they have been approved.  To change a label, market a new dosage or strength of a drug, or change the way it manufactures a drug, a company must submit a supplemental new drug application (sNDA).   The supplement type refers to the kind of change that was approved by FDA.  This includes changes in manufacturing, patient population, and formulation.

 Tentative Approval 

If a generic drug product is ready for approval before the expiration of any patents or exclusivities accorded to the reference listed drug product, FDA issues a tentative approval letter to the applicant. The tentative approval letter details the circumstances associated with the tentative approval. FDA delays final approval of the generic drug product until all patent or exclusivity issues have been resolved. A tentative approval does not allow the applicant to market the generic drug product.

 Therapeutic Biological Product

A therapeutic biological product is a protein derived from living material (such as cells or tissues) used to treat or cure disease.

 Therapeutic Equivalence (TE)

Drug products classified as therapeutically equivalent can be substituted with the full expectation that the substituted product will produce the same clinical effect and safety profile as the prescribed product. Drug products are considered to be therapeutically equivalent  only if they meet these criteria:

  • they are  pharmaceutical equivalents (contain the same  active ingredient(s); dosage form and route of administration; and strength.)

  • they are assigned by FDA the same therapeutic equivalence codes starting with the letter "A ." To receive a letter "A", FDA

  • designates a brand name drug or a generic drug to be the Reference Listed Drug (RLD).

  • assigns therapeutic equivalence codes based on data that a drug sponsor submits in an ANDA to scientifically demonstrate that its product is bioequivalent (i.e., performs in the same manner as the Reference Listed Drug).

 Therapeutic Equivalence (TE) Codes 

The coding system for therapeutic equivalence evaluations allows users to determine whether FDA has evaluated a particular approved product as therapeutically equivalent to other pharmaceutically equivalent products (first letter) and to provide additional information on the basis of FDA's evaluations (second letter). Sample TE codes: AA, AB, BC (More on TE Codes)

  • FDA assigns therapeutic equivalence codes to pharmaceutically equivalent drug products. A drug product is deemed to be therapeutically equivalent ("A" rated) only if:

  • a drug company's approved application contains adequate scientific evidence establishing through in vivo and/or in vitro studies the bioequivalence of the product to a selected reference listed drug. 

  • those active ingredients or dosage forms for which no in vivo bioequivalence issue is known or suspected.

  • Some drug products have more than one TE Code.

  • Those products which the FDA does not deem to be therapeutically equivalent are "B" rated. 

Over-the-counter drugs are not assigned TE codes.

Source:  U.S. Food & Drug Administration, FDA

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