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Vaccines and Side Effects: The Facts

What about serious side effects? How often do they occur, and should you worry about them? This is an issue that has been studied repeatedly and intensively. Here are some facts that should help put your mind at ease.

Yes, there are reports of serious side effects that have been blamed on vaccines. But proving that the vaccine caused these side effects is often hard to do. In many cases, children simply develop illnesses around the time they’ve received a vaccine, and the immunizations get blamed unfairly. Don’t forget that infants and children are given vaccinations at a time in life when certain health conditions begin and become apparent to both parent and doctor. In most cases, the evidence just isn’t there to support a cause-and-effect link with vaccines.


That’s the case with the myth linking the diphtheria-tetanus-pertussis (DTP) vaccine with sudden infant death syndrome (SIDS). The first dose of the vaccine is administered when a baby is 2 months old, which coincides with the time of life when the risk of SIDS is highest. Thus, you would expect some SIDS deaths to occur in this age group, whether children receive the immunization. In fact, a number of studies dating back to the 1980s looked at the incidence of SIDS deaths occurring at the time of the DTP vaccine. The researchers concluded that the number of deaths was at a level about equal to the number that would be expected to take place by chance. In short, there just isn’t any scientific evidence linking the vaccine with SIDS. Even so, many of the myths surrounding vaccines seem to have a life of their own. Below, you’ll find a description of some of these unfounded claims, as well as a look at what the scientific evidence shows.

Measles-Mumps-Rubella Vaccine and Autism

Autism is made up of many chronic developmental disorders and is often first diagnosed in toddlers. The number of cases of autism is reportedly on the rise, and some critics insist that the measles-mumps-rubella (MMR) vaccine is to blame. Others say the increase can be attributed to better reporting of autism cases by doctors. In 2001 and again in 2004, the Institute of Medicine (IOM) Immunization Safety Review Committee, an independent body of experts who have no conflict of interest with pharmaceutical companies or organizations that make vaccine recommendations, studied a possible MMR-autism link and found no evidence supporting such a connection. A panel of experts brought together by the AAP reached the same conclusion. Most of the authors of the original study linking MMR to autism have retracted their support of the study.

Risks of Thimerosal?

Since the 1930s, some vaccines have included a mercury-containing preservative called thimerosal. It has been used as an additive to vaccines because of its ability to prevent contamination by bacteria or fungi. Critics have argued that thimerosal-containing vaccines are the cause of a number of neurologic and developmental disorders, ranging from autism to attention-deficit/hyperactivity disorder and speech and language delays. The IOM safety committee studied this issue and concluded that the evidence favors rejection of a causal relationship between thimerosal-containing vaccines and autism. Since the end of 2001, most of the vaccines recommended by the AAP are available in thimerosal-free formulations. Some vaccines, such as the MMR, polio, and chickenpox vaccines, have never contained thimerosal.

Multiple Immunizations and Immune Disorders

Because some immunizations are given together, parents are often concerned that multiple vaccines might trigger health problems associated with the immune system. Can they increase your child’s risk of infections? Can they lead to the development of type 1 diabetes or various allergic diseases including asthma? After looking at this issue, the IOM committee concluded that there is no evidence of a cause-and-effect relationship between multiple immunizations and a greater risk of infections and/or type 1 diabetes. As for a link with asthma and other allergic disorders, there simply isn’t enough evidence to either accept or reject a connection with multiple vaccinations given together.

Hepatitis B Vaccines and Multiple Sclerosis

Although critics have claimed that hepatitis B immunizations can cause or trigger a relapse of multiple sclerosis, the IOM safety committee could find no scientific support for this theory.  The same report also concluded that there is no evidence that the hepatitis B vaccine causes other types of nervous system problems, including Guillain-Barre syndrome.

Last Updated
Immunizations &Infectious Diseases: An Informed Parent's Guide (Copyright © 2006 American Academy of Pediatrics)
The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
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