Last week at a campaign event, John McCain was asked to comment on the connection between Autism and the presence of mercury in childhood vaccines. His response, according to ABC News, was: “It’s indisputable that [autism] is on the rise amongst children, the question is what’s causing it. And we go back and forth and there’s strong evidence that indicates that it’s got to do with a preservative in vaccines.”

McCain thus marched headlong into the bitter autism wars of the last few years, and placed himself firmly on the wrong side. There has certainly been a sharp rise in autism diagnoses in the last thirty years, though it is actually far from clear whether this is because the condition has become more common or tests for it have become more frequent and advanced. Either way there is no evidence-none, zero-connecting autism to vaccines.

The preservative McCain mentioned is called Thimerosal. Thimerosal does contain a form of mercury, though it is a form called ethyl mercury which metabolizes very quickly and does not remain in the body. But Thimerosal has been removed from childhood vaccines, with the exception of the flu vaccine, in an effort to reduce the overall exposure of children to mercury, which in very high concentrations (very much higher than those ever found in vaccines) can of course be harmful.

The decision to remove Thimerosal from vaccines was not motivated by any connection to autism, and indeed, despite years of intense study, no such connection has ever been shown. On the contrary, studies conducted since the removal of Thimerosal from vaccines have shown no consequent decrease in autism diagnoses.

The supposed connection was proposed in the 1990s by a study that has since been shown both methodologically and ethically flawed (as detailed by Caitrin Nicol in a recent issue of The New Atlantis). But unfortunately some parents of autistic children latched on to the theory, and have engaged in an intense public effort to link vaccines and autism in the public mind.

The effort has included a lobbying campaign in Washington, which relies on the energy and devotion of the parents involved. In 2005, while serving as the White House staffer charged with such issues, I received thousands upon thousands of faxes from one autism group demanding that the government immediately remove any vaccines containing Thimerosal from the market. Several members of Congress have been persuaded, and in fact one early version of the 2008 budget bill covering the department of Health and Human Services included a provision prohibiting funds in the federal Vaccines for Children program from paying for vaccines that contain Thimerosal. The Bush administration strongly opposed the provision, arguing it “could result in children not receiving any flu vaccine,” and it was eventually removed.

But well beyond politics, the campaign has real consequences. By planting baseless fears in the minds of parents, it has caused a real decline in the number of children being vaccinated, which could contribute to the resurgence of some diseases thought to be things of the past, like mumps.

Autism is a very sensitive issue, and getting past the vaccine debate will require real care, and serious attention to the facts. Unfortunately John McCain showed neither in this instance, and his comment will no doubt needlessly extend the debate, as advocates of the vaccines-autism link point to his words for support, and (if he is elected) demand that he follow up with restrictions on vaccine availability. McCain should correct himself, and soon.