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Vaccine safety
Vaccines work best when as many people as possible receive them. When more people receive immunizations, the possibility of anyone being exposed to a vaccine-preventable disease is lower. The United States currently has the safest, most effective vaccine supply in history. By law, years of testing are required before a vaccine can be licensed. Once in use, vaccines are continually monitored for safety and effectiveness. The Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) continually work to make already safe vaccines even safer.
Thimerosal and autism
Thimerosal is a mercury-containing preservative. It has been in use since the 1930s to prevent contamination in multidose vials of vaccines. There is no convincing evidence of harm caused by the low doses of thimerosal in vaccines, except for minor reactions such as redness and swelling at the injection site. However, in July 1999 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. Since 2001, with the exception of some influenza vaccines, thimerosal is not used as a preservative in childhood vaccines. The American Academy of Pediatrics, the American Medical Association, the CDC and the Institute of Medicine agree that scientific research does not support a link between thimerosal in vaccines and autism.
Measles, mumps and rubella (MMR) vaccine and autism
In 1998, a study of autistic children published in “The Lancet” questioned a connection between MMR vaccine and autism. The 1998 study has a number of limitations. For example, the study was very small, involving only 12 children. This is too few cases to make any generalizations about the causes of autism. In addition, the researchers suggested that MMR vaccination caused bowel problems in the children, which then led to autism. However, in some of the children studied, symptoms of autism appeared before symptoms of bowel disease. In 2004, 10 of the 13 authors of the 1998 study retracted the study's interpretation. The retraction appeared in the March 6, 2004, edition of “The Lancet.” The authors said the data did not establish a causal link between the MMR vaccine and autism. No published scientific evidence exists that shows any benefit from separating the combination MMR vaccine into three individual shots.
In 2004, a report by the Institute of Medicine concluded there is no association between autism and the MMR vaccine or vaccines that contain thimerosal as a preservative.
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