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Autism Spectrum Disorders Health Center

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New Intensity to Debate Over Autism Cause

Parents and Researchers Grapple With Claims That Autism Is Linked to Thimerosal in Vaccines


"When we first heard the IOM committee was meeting, we said the meeting was premature," Safe Minds' Bernard tells WebMD. "We told them to wait, that more research is coming out. They ignored us. They went ahead and had their meeting and missed a lot of evidence."

WebMD asked committee chairwoman Marie C. McCormick, MD, ScD, to comment. McCormick is professor of maternal and child health at Harvard School of Public Health.

"We had to make two kinds of assessments," McCormick tells WebMD. "One was, did we see any evidence thimerosal was associated with autism. We had five epidemiologic studies. None were perfect. But all pointed in the same direction of no association."

Those five studies included five observational studies, using different methods, looking for an association between autism and vaccination in Sweden, Denmark, the U.S., and the U.K. None was found. Autism rates continued to rise even after thimerosal was removed from vaccines.

Each of the studies had flaws. But they weren't nearly as flawed as Kennedy suggests, says IOM spokeswoman Christine Stencel.

"The IOM committee certainly knew of these issues and found the studies were relevant, that they were well designed, and that their data are valid," Stencel says.

But what of the "truckloads" of studies to which Kennedy points?

"We looked at basic science and asked if there was any indication of how thimerosal could cause autism," McCormick says. "We looked at over 200 scientific articles, and the evidence linking thimerosal to autism is purely theoretical at best."

This does not satisfy Bernard. She doesn't think the evidence proves thimerosal causes autism. But she does think the evidence points in that direction. If researchers don't follow up, she fears, valuable time will be lost.

"If you assume that there is a connection between mercury exposure and an outcome of autism, then by studying what mercury does, you will come a lot closer to learning how to treat these kids," Bernard says. "And if you find a role for mercury, we can do a lot more in terms of prevention. You can't just have effective treatment -- in today's science -- without understanding the root cause."

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