IOM Report: No Link between Vaccines and Austism: There Is No Link between Autism and the Measles-Mumps-Rubella (MMR) Vaccine or the Vaccine Preservative Thimerosal, According to a Report Released by the Institute of Medicine's (IOM) Immunization Safety Review Committee
Meadows, Michelle, FDA Consumer
The report, released in May 2004, was prepared by a committee of independent experts established by the IOM in 2001 at the request of the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH) to evaluate evidence on potential links between childhood vaccines and health problems. The agencies explored the issue because of growing controversy and questions from the public about vaccine safety.
Some parents have expressed concern because the symptoms of autism typically emerge in a child's second year of life, around the same time children first receive the MMR vaccine. Autism is a complex set of severe developmental disorders characterized by repetitive behavior and impaired social interaction and communication abilities. Other concerns the committee looked at include the use of thimerosal, a mercury-based compound used as a vaccine preservative, because many forms of mercury are known to damage the nervous system in high doses.
Review of the Research
This latest IOM report follows two reports on vaccines and autism published in 2001. The committee determined then that the evidence did not show an association between the MMR vaccine and autism, but that more evidence was needed regarding thimerosal. "The committee concluded that the evidence available at that time was inadequate to accept or reject a causal relationship between thimerosal and neurodevelopmental disorders," says Marie McCormick, M.D., Sc.D., chairwoman of the immunization safety committee and a professor at the Harvard School of Public Health.
The committee revisited these issues because several studies exploring possible links between vaccines and autism have been published since 2001. Committee members concluded that the hypothesis about how the MMR vaccine and thimerosal could trigger autism lacks supporting evidence. Their conclusions were based on a careful review of well-designed studies and other information from researchers and parents.
Five large studies in the United States, the United Kingdom, Denmark, and Sweden done since 2001 found no evidence of a link between autism and vaccines containing thimerosal. And 14 large studies consistently showed no link between the MMR vaccine and autism. The committee also reviewed several studies that did report associations between vaccines and autism and found that these studies had limitations and lacked supporting evidence.
The committee reviewed potential biological links between vaccines and autism and found them to be only theoretical. Examples of some of the hypothesized links include a suggestion that the measles virus in the MMR vaccine might lodge in the intestines and trigger the release of toxins that could lead to autism. Another hypothesis is that the MMR vaccine might stimulate the release of immune factors that damage the central nervous system. Yet another hypothesis is that thimerosal may interfere with biochemical systems in the brain, thereby causing autism. But according to the IOM report, no evidence has slaown that the immune system or its activation play a direct role in causing autism, and autism has not been documented as being a result of exposure to high doses of mercury.
"There is no convincing evidence of serious harm from the low doses of thimerosal in vaccines," says Karen Midthun, M.D., deputy director for medicine in the FDA's Center for Biologics Evaluation and Research (CBER). …