Vaccines = autism? Scientists say no.

No link between autism and childhood vaccines has been proven, but the mere suggestion has had a negative impact on public health. Unvaccinated children have succumbed to and spread diseases that could have been prevented, as parents in eight states pushed legislation to restrict certain substances in childhood immunizations they believe could cause autism.

But the entire outcry may be unwarranted, according to a recent report by the Institute of Medicine at The National Academies.

Certain parent groups have claimed that thimerosal, a mercury-based preservative used in some vaccines and other products since the 1930s, may cause autism. The 2004 report concluded that there is no association between autism and vaccines that contain thimerosal.

The Food and Drug Administration (FDA) Modernization Act called in 1999 for a study of the risk of all mercury-containing food and drugs. As part of this effort, the FDA conducted a review of mercury content in vaccines.

The FDA's review, however, found no evidence of harm caused by doses of thimerosal in vaccines, except for minor local reactions. Nevertheless, in July 1999 the Public Health Service agencies, the American Academy of Pediatrics and vaccine manufacturers agreed that thimerosal levels in vaccines should be reduced or eliminated as a precautionary measure.

The consequent publicity in 1999 led some parent groups to campaign against use of the vaccines--not just the preservative.

Today, all routinely recommended early childhood vaccines in the United States, except the flu vaccine, contain only trace amounts of thimerosal or none at all. In addition, the MMR vaccine, the chickenpox and the polio vaccines have never contained thimerosal.

The Institute of Medicine Immunization Safety Review Committee, which examined the information and consists of expert physicians and scientists, who have no connections to the pharmaceutical industry, recommends that future autism research look into causes other than vaccines.

Iowa passed a bill banning the administration of any vaccine that contains more than a trace of thimerosal. The new law does not apply to early childhood immunizations for influenza or during an emergency or epidemic. At press time, a similar bill in California was waiting for the governor's signature.