3/5/08 Update: Asked about autism again at an event yesterday, Sen. McCain did not continue to draw the connection between the disorder and vaccine preservatives, but instead stressed the need for continued research and more funding for education.
Politicians often make bold policy statements, but rarely wade into the more uncertain waters of biological research. That is why many were surprised to hear presidential candidate John McCain confidently state, in reference to autism at a town hall meeting in Texas:
It’s indisputable that autism is on the rise among 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.
These statements are actually quite disputable, in at least three ways. On the most general level, they are unwise because they use extreme language to convey absolute certainty. Scientific theories of biological causation are rarely certain, but the cause of autism is particularly murky. There have been dozens of hypotheses, from genetic mutations to poor parenting to environmental toxins. None of these has been confirmed, in part because there are no certain biological markers for autism, making epidemiological research more difficult.
The absence of biological markers leads to the second objectionable part of the statements, that "autism is on the rise". While it is indisputable that the number of children diagnosed with autism has been rising in the 21st century, these numbers need nuanced analysis. Due to intensified study and public awareness campaigns, parents and doctors are much more likely to notice social abnormalities and to advocate for a diagnosis. This may result in the proper diagnosis of many children who would previously have slipped through the cracks entirely, or been diagnosed with other behavioral disorders like ADHD.
Even if autism diagnoses are rising, this would actually undermine McCain's last point that the cause is preservatives in vaccines because those preservatives were discontinued years ago. It is true that the shelf-life of certain vaccines was extended with thimerosal, a type of mercury, but studies have shown that this type of mercury is expunged from the body much quicker than the dangerous mercury often consumed in fish. Still, it is probably a good thing that thimerosal is no longer used, because mercury can sometimes cause irreparable damage and there is no reason to take any risk with out children, however small. Ultimately, it seems unlikely that thimerosal is the culprit because diagnoses have increased even after it was removed. There is no "strong evidence"; in fact, none of the over 5000 pharmaceutical lawsuits have presented enough evidence to win a trial.
Political candidates stumping for office often talk about how things ought to be, a practice that is incompatible with the progress of science through cautious observation and incremental improvement. Autism, like many issues in mental health, remains a subject of intense research and debate. It's important that politicians encourage continued discovery and betterment of human health, based on scientific evidence and research, and build policy around facts that have achieved a scientific consensus.
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