Vaccines = autism? Scientists say no.

• Position: Trends And Transitions

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...