Autism is one of the most severe and disruptive of all childhood disorders - with a high level of disruption that of course lasts well into adulthood. With both genetic and environmental elements at work in it, autism (which affects boys at least three times more often than girls and is found in all races and throughout the world) is a communicative disorder that interferes with an individual's ability to form social relationships as well as to communicate with others. As might well be expected to be the case with any severe condition the etiology of which is understood a number of "folk" explanations for the condition have developed, including the idea that childhood vaccinations (and especially the mercury-based preservative Thimerosal that is used in the formulation of many vaccines) is responsible for triggering the condition. This paper argues against any connection between Thimerosal and autism (or rather argues that no such condition has yet been established; it would not be good science to argue that such a connection will never be established). However, and this is an important initial caveat to make, simply because no connection has been found does not mean that all such "folk" explanations of medical or scientific phenomena should be dismissed. Scientists, and especially medical researchers, are sometimes too quick to assume that those who lack formal training in the sciences are entirely unqualified to make the kinds of observations that lead to scientific breakthroughs, but this is simply not true. Anyone who is intelligent and careful can make important, scientific observations about the world around us. This is what parents, baffled by the affects of autism on their children, have attempted to do: The fact that they have (in so far as current scientific investigation has so far consistently demonstrated) been wrong does not mean that any future claims about the world by non-scientists can be dismissed out of hand rather than through careful scientific evidence.

It seems unlikely that advocacy groups would have looked to Thimerosal as a possible cause of autism if the disease were itself better understood. However, it remains one of the most mysterious...

Autism is distinguished by a number of often dramatic and sometimes even violent symptoms that often prevent autistic children from being educated and prevent autistic adults from forming non-familial relationships or holding down jobs. Autism is primarily marked by significant withdrawal from the world and an extreme aversion to entering the social spaces of other people as well as by a range of behaviors that may appear bizarre to others (Smith etal, 1994; Paluszny, 1979).
A number of studies have investigated whether there is any link between childhood vaccines and autism. Such a link was originally proposed by the children of parents with autism, in part because the symptoms of autism often appear soon after vaccinations (this is not surprising since the onset of autistic symptoms tends to occur at the same time in all children; this age is also - for unrelated reasons - the time at which most children are receiving one of their sets of childhood vaccines. The other reason that Thimerosal has been selected by advocacy groups as a possible cause (or if not cause at least "trigger" of autism) is that it is a mercury-based product. Most people are aware of the fact that mercury in some forms is highly toxic; it is not therefore surprising that parents whose children have been diagnosed as autistic after being vaccinated with a serum that contains mercury should question its safety. However, as the Federal Drug Administration notes, it is important to understand the properties of the specific mercury compound in question:

Thimerosal, which is approximately 50% mercury by weight, has been one of the most widely used preservatives in vaccines. It is metabolized or degraded to ethylmercury and thiosalicylate. Ethylmercury is an organomercurial that should be distinguished from methylmercury, a related substance that has been the focus of considerable study (http://www.fda.gov/cber/vaccine/thimerosal.htm#thi).

Methylmercury is a neurotoxin of considerable potency; the toxicity of ethylmercury is certainly lower, although it may prompt allergic reactions and (as is true of all substances)…