Mercury rising: exposing the vaccine-autism myth

Skeptic, Fall, 2007 by Matthew Normand, Jesse Dallery

ON JUNE 11, 2007, NEARLY 5,000 PARENTS OF autistic children fried a lawsuit against the federal government, claiming that childhood vaccines (specifically the mercury-containing thimerosal in the vaccines) caused their children's autism. The previous year the New York Times ran a column that was skeptical of the alleged link between autism and vaccines. It generated the following comment on an Internet message board, typical of the anecdotal analyses that perpetuate the claim:

   You say, "There is no proven link" between mercury and autism.
   There also is "no proven link" between going outside in the rain
   and cold without a hat or coat and getting the sniffles. Look at
   the data: the epidemic of autism mirrors the administration of
   vaccines with mercury. Now that they are off the shelves (more or
   less), the cases are going down.

Here we see how the writer dismisses scientific evidence that fails to support a link between cold and illness and vaccines and autism in favor of her personal experiences. And the vaccine-autism controversy is not constrained to a small fringe group of parents or advocates. Increasingly, people of position and power are leaping into the fray, spurred on by vocal groups demanding action. For example, an article by Robert E Kennedy, Jr. appeared in a June 2005 issue of Rolling Stone magazine] that alleged thimerosal-containing vaccines were at the heart of the autism epidemic and, moreover, that the government was aware of this and actively engaged in a cover-up.

This article makes five points concerning the relation between thimerosal-containing vaccines and autism: (1) the dangers of mercury are well established, but this does not lead inexorably to a relationship between vaccines containing thimerosal and autism; (2) a number of well controlled studies have failed to uncover any correlation between the delivery of the vaccines and the onset of autism; (3) even if some correlation existed there are a number of alternative explanations for the correlation that do not assume any causal relationship between the vaccine and autism; (4) much attention has been given to a possible government cover up, which is certainly of concern if true but is otherwise independent of the problems with claims of a link between thimerosal and autism; and (5) the type of public hysteria manifested in the current controversy is not new and we would be well served to learn from similar controversies of recent times.

Mercury, Thimerosal, and the Potential for Harm

Science has told us unequivocally that mercury is bad for our bodies. In sufficient doses, mercury kills cells that it contacts, causes neurological damage in humans and other animals, and generally wreaks havoc on living things. Yet since the 1930s, thimerosal has been used as a preservative in vaccines. (2) One of the breakdown products of thimerosal is ethylmercury, which is an organic compound of mercury. Public concern about thimerosal is certainly understandable, but does this mean that concern about a link between vaccines and autism is justified as well? In a word, no. Mercury might do a number of nasty things to the human body, and concern about it is therefore justified, but that does not mean it causes autism.

Ethylmercury is not the same thing as its cousin, methylmercury. Cumulative and high doses of methylmercury can produce renal and neurologic damage. It can build up in the brain and stay in the body for a long time. Ethylmercury is more, well, mercurial. It is expelled rapidly from the body and does not accumulate. Nevertheless, guidelines for the ingestion of ethylmercury were based on those for methylmercury. Around the same time these guidelines were formalized, children were receiving more vaccines that contained thimerosal. For example, in the early 1990s the Haemophilus influenzae b and hepatitis B became staple features of the vaccine schedule for infants, which already included another thimerosal-containing vaccine (diphtheria tetanus and variants). Based on the very conservative guidelines established by the Environmental Protection Agency (EPA), it was concluded that by age two some children might be receiving excessive levels of ethylmercury when considered in the context of known risks of methylmercury exposure. (3)

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Against this backdrop enter skyrocketing rates of autism diagnoses. In California, the Department of Developmental Services reported a 273'% increase from 1987 to 1998 in the number of individuals served under the category of autism. (4) Surely this increase in rates was caused by an environmental source, right? In 2001, the Institute of Medicine (IOM) Immunization Safety Review Committee held a public meeting to address the link between one environmental source--thimerosal and autism. At the meeting, Mark Blaxill, a board member of a nonprofit organization dedicated to investigating the risks of mercury exposure, presented a graph showing the estimated cumulative dose of thimerosal to the estimated prevalence of autism in California. (5) The increasing trend lines during the early 1990s were right on top of each other, about as dose as you can get to perfect correlation in ecological data. Such orderly correlations are all that it takes to convince the uncritical eye.