"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."Probably the same kind of 'strong evidence' that there were WMDs in Iraq. But this isn't really about McCain per se - there is no shortage of people who share this stance - it's about the idea that mercury-based preservatives (thimerosal) in vaccines are responsible for a rise in autism.
First of all, is it even true that autism and autism spectrum disorders (ASD) are on the rise? It's possible that what we're seeing is an increase in diagnosis of ASD rather than an increase in the disorders themselves - either due to improved diagnostic tests or changes in the way these disorders are classified. This paper from the journal Pediatrics puts some numbers to that idea and shows that autism diagnoses took an upswing at the same time that diagnoses of mental retardation and learning disability declined suggesting that changes in diagnostics may explain the apparant autism epidemic. Orac at Respectful Insolence blogs about this paper in greater depth.
Regardless of whether autism is actually on the rise or not, it's still important to find out the underlying cause. Are mercury-containing vaccines the culprit? The science says no. A link between thimerosal-containing vaccines is not supported by science. Several studies have been done that show no causal link between mercury in vaccines and autism.
"But still," some will say, "we avoid eating certain fish because of mercury levels, so having it in vaccines makes no sense." First of all, the mercury build-up in fish (methyl-mercury) is different from the form in thimerosal (ethyl-mercury). Ethyl-mercury has a much shorter half life and does not build up in the body the same way. And that's beside the point: in the US thimerosal hasn't been used as a preservative in recommended childhood vaccines since 2001. Yet in the US and other countries that no longer use thimerosal, autism diagnoses continue to rise. This tells us that it's not the mercury, but more likely - as mentioned above - changes in the way autism spectrum disorders are identified.
For those who refuse getting vaccinated "to be on the safe side": Don't. Vaccines are responsible for the eradication of smallpox, near-eradication of polio and a host of other diseases (presumably, this is why anti-vaxers feel they can get away with it - because there's little fear of smallpox, polio and the like). Not receiving these routine childhood vaccinations has real public health implications. It's irresponsible to not have your children vaccinated.
As for John McCain, it's irresponsible for HIM to make such strong claims about a connection between mercury in vaccines and an autism epidemic. He needs to surround himself with better science advisors than that.
*Clinton says: "I am committed to make investments to find the causes of autism, including possible environmental causes like vaccines. [...] I will ensure that all vaccines are as safe as possible for our children by working to ensure that Thimerosal and mercury are removed from vaccines."
Obama says: "An Obama administration will go where the science and the facts lead us, whether it is about climate change or toxic heavy metals in our environment. [...] I support the removal of thimerosal from all vaccines and work to ensure that Americans have access to vaccines that are mercury free."
(source: Age of Autism)
Some people argue that these viewpoints are worse than the stronger McCain statement.