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General Vaccine Safety Concerns

Are vaccines safe?

The first definition of the word safe is "harmless." This definition would imply that any negative consequence of a vaccine would make the vaccine unsafe. Using this definition, no vaccine is 100 percent safe. Almost all vaccines can cause pain, redness or tenderness at the site of injection. And some vaccines cause more severe side effects. For example, the pertussis (or whooping cough) vaccine can cause persistent, inconsolable crying, high fever or seizures associated with fever. Although none of these severe symptoms result in permanent damage, they can be quite frightening to parents.

But, in truth, few things meet the definition of "harmless." Even everyday activities contain hidden dangers. For example, every year in the United States, 350 people are killed in bath- or shower-related accidents, 200 people are killed when food lodges in their windpipe, and 100 people are struck and killed by lightning. However, few of us consider eating solid food, taking a bath, or walking outside on a rainy day as unsafe activities. We just figure that the benefits of the activity clearly outweigh the risks.

The second definition of the word safe is "having been preserved from a real danger." Using this definition, the danger (the disease) must be significantly greater than the means of protecting against the danger (the vaccine). Or, said another way, a vaccine's benefits must clearly and definitively outweigh its risks.

To better understand the definition of the word safe when applied to vaccines, let's examine four different vaccines and the diseases they prevent:

Is the hepatitis B vaccine safe?

The hepatitis B vaccine has few side effects. However, one side effect is serious. About one of every 600,000 doses of hepatitis B vaccine is complicated by a severe allergic reaction called anaphylaxis. The symptoms of anaphylaxis are hives, difficulty breathing and a drop in blood pressure. Although no one has ever died because of the hepatitis B vaccine, the symptoms of anaphylaxis caused by the vaccine can be quite frightening.

On the other hand, every year about 5,000 people die soon after being infected with hepatitis B virus. In addition, about 10,000 people every year suffer severe liver damage (called cirrhosis) or liver cancer caused by hepatitis B virus. People are much more likely to develop these severe and often fatal consequences of hepatitis B virus infection if they get infected when they are very young children. For this reason, the hepatitis B vaccine is recommended for newborns.

Some parents wonder whether it is necessary to give the hepatitis B virus vaccine to newborns. They ask: "How is a baby going to catch hepatitis B?" But, before the hepatitis B virus vaccine, every year in the United States about 18,000 children less than 10 years of age caught hepatitis B virus from someone other than their mother. Some children catch it from another family member, and some children catch it from someone outside the home who comes in contact with the baby. About 1 million people in the United States are infected with hepatitis B virus. However, because hepatitis B virus can cause a silent infection (meaning without obvious symptoms), many people who are infected with hepatitis B virus don't know that they have it! So it can be hard to tell from whom you could catch hepatitis B virus. Worse yet, many people don't realize that you can catch hepatitis B virus after coming into contact with minute quantities of blood through casual contact with someone who is infected (for example, sharing washcloths or toothbrushes). In fact, a milliliter of blood (about one-fifth of a teaspoon) from someone who is infected can contain as many as one billion infectious viruses, so people can be infected with quantities of infected blood small enough that they are not visible to the naked eye.

Because the benefits of the hepatitis B vaccine clearly and definitively outweigh its risks, the hepatitis B vaccine is safe.

Was the old pertussis vaccine safe?

The old pertussis vaccine had far more risks than the hepatitis B vaccine. The old pertussis vaccine was called the "whole-cell" vaccine and had a high rate of severe side effects. Persistent, inconsolable crying occurred in one of every 100 doses, fever greater than 105 degrees occurred in one of every 330 doses, and seizures with fever occurred in one of every 1,750 doses. Due to negative publicity related to this vaccine, its use decreased in many areas of the world.

For example, the Japanese Ministry of Health decided to stop using the pertussis vaccine in 1975. In the three years before the vaccine was discontinued, there were 400 cases of pertussis and 10 deaths from pertussis in Japan. In the three years after the pertussis vaccine was discontinued, there were 13,000 cases of pertussis and 113 deaths! It should be noted that although the side effects of the pertussis vaccine were high, children didn't die from pertussis vaccine; however, they die die from pertussis infection. The Japanese Ministry of Health, realizing how costly their error had been, soon reinstituted the use of pertussis vaccine.

The children of Japan proved that, despite the side effects, the benefits of the old pertussis vaccine clearly outweighed the risks.

Scientific progress eventually led to the creation of another version of the pertussis vaccine. Known as the “acellular” pertussis vaccine, it was more purified, so instead of containing about 3,000 immunogenic proteins, it only contained two to five proteins. The ("acellular") pertussis vaccine became available in the United States in 1996. Children who received this vaccine had a much lower risk of severe side effects than those who received the old "whole-cell" vaccine. Therefore, the new pertussis vaccine is safer than the old pertussis vaccine. But because the benefits of the old pertussis vaccine outweighed its risks, it too was safe.

Is the pneumococcal vaccine safe?

Let's take a look at the pneumococcal vaccine. The pneumococcal vaccine was licensed in the United States in the year 2000 and was recommended for use in all children less than 5 years of age. Some parents chose to take a "wait-and-see" attitude. They reasoned that because the problems with the rotavirus vaccine were not revealed until the vaccine was given to 1 million children (see below, "Is the rotavirus vaccine safe?"), why not wait and see what happened after the pneumococcal vaccine was given to several million or more children.

However, the choice not to give the pneumococcal vaccine was not a risk-free choice. Before pneumococcal vaccine was first given to infants in 2000, every year in the United States about 700 children (less than 5 years old) got meningitis, 17,000 got bloodstream infections, and 71,000 got pneumonia from pneumococcus. So the choice not to give a pneumococcal vaccine was a choice to risk the severe, often permanent, and occasionally fatal consequences of pneumococcal infection. Parents should be reassured by two facts. First, the pneumococcal vaccine was tested in about 20,000 children before it was licensed for use. Second, the Haemophilus influenzae type b (Hib) vaccine is made in a manner almost identical to the pneumococcal vaccine (see How Are Vaccines Made?) and has been given safely to millions of children since 1990.

Is the rotavirus vaccine safe?

A new rotavirus vaccine was recommended for use in February 2006. This vaccine was tested in more than 70,000 infants. About half of the children received vaccine and the other half received a salt water solution. This large study showed the vaccine to be safe. Children who received the vaccine were not more likely to experience vomiting, diarrhea, fever, irritability or poor feeding than children who did not receive the vaccine.

The first rotavirus vaccine was withdrawn from use because of a problem with safety. The vaccine was found to cause a rare, but potentially very serious, side effect called intussusception. Intussusception occurs when one section of the small intestine folds into another section of the intestine. When this happens, the intestine can become blocked. Intussusception is a medical emergency, and children can die from the disease. The rotavirus vaccine was given to about 1 million children in the United States between 1998 and 1999. About one of every 10,000 children who were given the vaccine got intussusception (a total of about 100 children), and one child died because of the vaccine.

Because of the problem with intussusception in the previous vaccine, any new rotavirus vaccine had to be evaluated for this potential side effect as well. There are currently two rotavirus vaccines (RotaTeq® and Rotarix®) available in the U.S. Studies have shown that children who receive either of the rotavirus vaccines are no more likely to experience intussusception than those who did not receive the vaccine. Intussusception occurs naturally in about 1 of every 100,000 infants.

Systems are in place to protect children against rare side effects from vaccines

The previous rotavirus vaccine is an example of how rare side effects can be detected quickly. The rotavirus vaccine was tested in about 11,000 children before it was submitted to the FDA for licensure. After the vaccine was licensed and recommended for use (see below, "Who licenses, recommends and requires vaccines?"), the vaccine was given to about 1 million children.

A system called the Vaccines Adverse Event Reporting System (VAERS) initially found about 15 cases of an intestinal blockage called intussusception soon after administration of the vaccine. This was worrisome enough to the Centers for Disease Control and Prevention (CDC) to cause them to temporarily suspend use of the rotavirus vaccine until it could be determined whether the vaccine did, in fact, cause intussusception. Their analysis showed that intussusception occurred in about one of every 10,000 children who received the vaccine. Because only 11,000 children were tested before the vaccine was licensed, it was really not possible to pick up such a rare side effect. The result of the rotavirus vaccine experience is that at least 60,000 children had to be tested before the next vaccine was licensed.

Several other systems of study to understand the rate of vaccine side effects, such as the Vaccine Safety Data Link (VSD), are also available. The VSD also allows one to determine the background rate of side effects, meaning the rate of adverse events in children who don't receive a vaccine. So, in many ways, systems like the Vaccine Safety Data Link are better than VAERS because they allow one to determine whether a particular vaccine is the cause of a rare side effect.

In A Look at Each Vaccine, we discuss the risks and benefits of every vaccine in order to determine whether these vaccines are safe. 


Who licenses, recommends and requires vaccines?

Vaccines are only given to children after a long and careful review by a number of different groups. These different groups either: license, recommend or require vaccines.


The first of three processes, licensure, involves gaining approval from the Food and Drug Administration (FDA). As a result, it is the longest of these processes. It can take years, even decades, before pharmaceutical companies can actually start providing the vaccine. For example, the varicella vaccine took about 11 years to be licensed by the FDA.

Vaccines are usually made by first showing that they are safe and effective in experimental animals. Once this is established, the vaccine becomes an Investigational New Drug (IND) and the company is given an IND license to further study the safety and effectiveness of the vaccine in adults, and eventually, children. Again, these trials can take years, giving companies ample time to provide the FDA with proof of long-term safety and effectiveness.

Read more about pre-licensure studies»


The "recommendation" process begins only after a vaccine is licensed by the FDA. Doctors don't just decide to start giving the vaccine on their own. They seek the recommendations of the Advisory Committee on Immunization Practices (ACIP), which is part of the Centers for Disease Control and Prevention (CDC), the Committee on Infectious Diseases of the American Academy of Pediatrics (AAP), and the American Academy of Family Physicians (AAFP).

While the FDA licensure process involves determining the risks versus the benefits of a particular vaccine, the recommendation process considers the costs versus the benefits. Here's the distinction:


Just because a vaccine is recommended for use doesn't mean that it is required for use. State legislatures and health departments determine whether a vaccine is required. They examine the practicality of requiring it for every child within the state. Factored into this equation is whether a local or state government can afford to pay for the vaccines of children whose parents can't afford it.

From a parent's perspective, vaccine requirements shouldn't matter. If a vaccine is considered to be safe and effective by the FDA, and useful for children by the ACIP, AAP and AAFP, then the vaccine is of value and should be given. Local health care budgets, although they determine whether a vaccine is to be required for school entry, have little to do with whether a vaccine is safe, effective and useful.


Why do we still need vaccines?

We still need vaccines for the following reasons:


Is natural infection better than immunization?

It is true that natural infection almost always causes better immunity than vaccines. Whereas immunity from disease often follows a single natural infection, immunity from vaccines usually occurs only after several doses. However, the difference between vaccination and natural infection is the price paid for immunity.

The price paid for immunity after natural infection might be pneumonia from chickenpox, mental retardation from Haemophilus influenzae type b (Hib), pneumonia from pneumococcus, birth defects from rubella, liver cancer from hepatitis B virus, or death from measles.

Immunization with vaccines, like natural infections, induces long-lived immunity, but unlike natural infection, does not extract such a high price for immunity.

Of interest, a few vaccines induce a better immune response than natural infection:


Reviewed by: Paul A. Offit, MD
Date: April 2013

Materials in this section are updated as new information and vaccines become available. The Vaccine Education Center staff regularly reviews materials for accuracy.

You should not consider the information in this site to be specific, professional medical advice for your personal health or for your family's personal health. You should not use it to replace any relationship with a physician or other qualified healthcare professional. For medical concerns, including decisions about vaccinations, medications and other treatments, you should always consult your physician or, in serious cases, seek immediate assistance from emergency personnel.


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