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Vaccine Safety

Concerns About Vaccine Safety

Updated: 09/26/2007

Decades ago, when thousands of children and adults in the United States contracted smallpox, diphtheria, poliomyelitis or measles each year, (1) vaccine safety concerns were not very common. People were more afraid of the diseases themselves than of possible side effects of the vaccines. Because of the success of vaccines, the situation is very different today: the diseases aren’t feared and concerns about vaccine safety are common.

Fortunately, the majority of parents understand the benefits of immunizations. But it is hard for some to appreciate risks that they don’t see. For example, most parents today have never seen a child paralyzed by polio, or choking to death from diphtheria, or brain damaged by measles. As a consequence, fear of these diseases does not—but should—haunt parents as it did historically.

It is also difficult to understand the importance of new vaccines that target illnesses that many know little about, like a vaccine to prevent infection by the sexually-transmitted human papillomaviruses (HPV). Looking at an innocent 10 year old, it is hard to imagine her being sexually active, much less her being at risk of cervical cancer decades later because she wasn’t vaccinated against HPV, a common infection that causes no symptoms.

While no vaccine is 100% safe, serious side effects are rare. However, because many vaccines are given to children at the ages when developmental and other problems are first being recognized, some parents may think that vaccines are to blame—it is difficult to grasp that the coincidence of timing does not mean that the vaccine caused the problem.

To compound the problem, the media carries stories about children whose parents believe that their child has been harmed by a vaccine, naturally causing concerns among other parents. And then, when parents try to get more information on the Internet, their concerns can be further heightened because the information they find may seem reasonable—but may be very wrong.

The vaccine-preventable diseases are not gone

Although we personally don’t see them very often, (2) these illnesses are very much waiting for an opportunity to return. Except for smallpox (for which we no longer give vaccine), the vaccine-preventable diseases are still here. For example, tetanus—which does not spread from person-to-person—is still in the soil; cases of mumps and rubella (and congenital rubella) continue to occur; and measles—the most contagious disease—is active many places in the world, often arriving in our midst by airplane.

When an unimmunized child develops a vaccine-preventable disease, the child gets all the risks of that disease: 1-4 per thousand will die from measles, half will die from tetanus, 1-2 per hundred will develop paralytic polio, and so on.

Much of the protection against vaccine-preventable diseases that we have in our country is because so many children are immunized. Having many immunized children indirectly protects those who cannot get vaccine and protects those children for whom the vaccine didn’t work—because no vaccine protects 100% of those who get it. Indirect protection occurs because susceptible children are not exposed to the disease-causing agents.

That is why we need to continue giving vaccines, even if we don’t see the diseases they prevent. To not immunize a child can have tragic consequences for the child, the child’s family, and for the child’s classmates and friends.

Vaccine safety concerns and risk perception

No vaccine is 100% effective; no vaccine is 100% safe. As with any drug, there are risks and side effects with vaccines, although serious side effects are rare. However, there is a much higher standard of safety expected of preventive vaccines than for drugs because vaccines are given to many people most of whom are healthy.

For example, people tolerate far less risk from the vaccine used to prevent infection with Haemophilus influenzae type b than they do the antibiotics that are used to treat the infections it causes.

Research shows that people respond better to some types of risks than others. Natural risks (such as infections for which there are no vaccines) are better tolerated than manmade risks (such as vaccine side effects). Also, risks that affect adults are better tolerated than risks affecting our children. Risks that are perceived to have unclear benefits may be less tolerated than risks where the benefits are understood.

For example, because measles, mumps and rubella (MMR) are no longer epidemic in the United States, some parents incorrectly assume that the risks of contracting the diseases are lower than the risk of their child experiencing an adverse reaction to MMR vaccine. They conclude that there may be little benefit from immunizing their child, hence there may seem to be no reason to take the risk of an adverse event. However, serious side effects from the MMR vaccine are rare—but there have been introductions of measles from other countries, cases of rubella and a large outbreak of mumps in 2006. (2) These infections remain a risk to children and communities; many are “just a plane ride away”.

Perception of risk depends on people’s experiences and knowledge. A person who experienced an adverse event after vaccination—or thinks that they know someone who did—will perceive vaccines as riskier than a person who has not. Conversely, one who has survived a vaccine-preventable disease—or a physician who has had to treat that disease—will likely be an advocate for vaccines.

Many vaccines are given to children at the ages when developmental and other problems are being recognized for the first time. Because something happened at about the same time that a vaccine was given, does not mean that one caused the other.

Missing information

Information may be available but that information may be unknown. Families need to be aware of the risks of exposure to infection, the importance of the proportion of children who are immune, and what the actual risks of complications from the different infections are. Without this information, families are uninformed and may develop a false sense of security and regard immunizations as unimportant.

For example, many are unaware that their community is at risk for exposure to the vaccine-preventable diseases. Others may not realize that their child could become ill if exposed to a vaccine-preventable disease—even if their child has received the vaccine.

In contrast to the uninformed, needed information may just not exist. For example, when a vaccine safety concern is first suggested, the necessary data to support or reject the hypothesis may not yet have been collected—in fact sometimes this may take several years of research.

The experience concerning the concern that thimerosal in vaccines might cause autism—first suggested in 1999—is illustrative of this. In 2001, when the Institute of Medicine’s Immunization Safety Review Committee first examined the issue, there was little data available about exposure to thimerosal in vaccines among children who subsequently were recognized as being autistic. Thus the Committee was unable to say that there was no such association. By 2004, however, much more scientific data was available and the IOM Committee concluded that there was no association between vaccines and autism. (3)

Misinformation (false or misleading information)

The uninformed person can unwittingly spread misinformation. However, there are also intentional misinformers, who actively seek to mislead others.

Unfortunately, the timing and widespread use of vaccines make them easy scapegoats to be blamed for all sorts of serious illnesses, particularly those diseases that are poorly understood. Of course not all vaccine safety concerns are misinformation—only those that persist despite the evidence against them.

Misinformation tends to rely on emotion-filled stories about bad things that happened to children or were first recognized—coincidental in time with vaccine administration. Misinformation is often presented with distorted or misquoted scientific studies.(4

Many media stories use faulty reports and parental concerns to depict a “controversy” about vaccines, failing to mention that the scientific community does not feel that a controversy exists. For example, in spite of the substantial evidence now available that allows rejection of the hypotheses that vaccines cause autism, there are some who continue to state that they do. These claims now fall into the category of misinformation but may continue to be portrayed in media stories as ‘controversies’.

Does it matter if other children are not vaccinated?

The unimmunized child is at risk from vaccine preventable diseases. For example, a couple in Tennessee, confused about vaccine safety because of what they had read on the Internet, decided to delay their daughter’s vaccinations. Some time later, the baby girl was stricken with a form of meningitis that could have been prevented by a vaccine. (5

In addition to a child’s personal risk, the unimmunized child puts all children at risk because unimmunized children are more likely to acquire—and they are more likely to spread—vaccine preventable diseases within the community. (6-8)

This is the reason why all parents should be concerned when other parents do not have their children fully immunized.


1. CDC. (1999). Impact of vaccines universally recommended for children—United States, 1900-1998. MMWR 48(12): 243-8.

2. CDC. (2007). Table 2. Reported cases of notifiable diseases, United States-2006. MMWR 56(33): 853-63

3. Institute of Medicine. Immunization Safety Review: Vaccines and Autism. Washington, DC: National Academies Press 2004.

4. Wolfe RM, Sharp LK, Lipsky MS (2002). Content and Design Attributes of Antivaccination Web Sites. JAMA, 287:3245-3248.

5. Snyder B. Vaccines’ safety, morality hit home for girl’s parents. The Tennessean, September 17, 2000.

6. Salmon DA, Haber M, Gangarosa EJ, et al. (1999). Health Consequences of Religious and Philosophical Exemptions From Immunization Laws: Individual and Societal Risk of Measles. JAMA 282:47-53.

7. Gangarosa EJ, Galazka AM, Wolfe CR, et al (1998). Impact of anti-vaccine movements on pertussis control: the untold story. Lancet, 351(9099):356-361.

8. CDC. (2006). Mumps outbreak at a summer camp—New York, 2005. MMWR 55(7): 175-7.

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