John McCain hopped into the autism/thimerosal debate last week when he related, “It’s indisputable that autism is on the rise among children….and there’s strong evidence that indicates that it’s got to do with a preservative in vaccines.” (Hat tip: Campaign K-12; also see On Special Education’s take on McCain’s argument.)
The trouble is that no decent study has ever established a link between autism and thimerosal. For example, consider this article published in JAMA, which compared kids exposed to vaccines with and without thimerosal and concluded, “The risk of autism and other autistic-spectrum disorders did not differ significantly between children vaccinated with thimerosal-containing vaccine and children vaccinated with thimerosal-free vaccine.” Or check out this literature review, published in Pediatrics, which also came to the same conclusion. What’s more, autism rates have continued to increase even after thimerosal was removed from kids’ vaccines.
Despite this body of evidence, advocacy groups like the National Autism Association continue to argue otherwise. They’re using a recent ruling in favor of an autistic child’s vaccination case to further trumpet this claim; check out their press release entitled, “Government Concludes Vaccines Caused Autism.”
The “autism epidemic” has received enormous press attention, but many reporters have neglected the diagnostic process. Is it possible that children who are now labeled autistic would have been classified as mentally retarded or learning disabled a few decades ago? According to a study published in Pediatrics by the University of Wisconsin’s Paul Shattuck, diagnostic substitution may account for a non-trivial proportion of increasing autism prevalence rates. Another article, published in the Journal of Autism and Developmental Disorders, concluded that diagnostic substitution may account for a third of the increase in autism cases. Shattuck nicely summarized this problem in his op-ed in the New York Times last year:
Most of the more mildly affected children who are considered to be on the spectrum today would never have qualified for an autism diagnosis using older criteria. This expansion of criteria makes it impossible to compare apples to apples when looking at data on long-term trends, because what counts as “autism” is simply quite different today.
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