An Investigation into the Supposed Link between Thimerosal-containing Vaccines and Autism

Thimerosal, a mercury-containing preservative used in vaccines, was implicated in 1997 to be linked to autism. Recent in vitro studies suggest that the concentration of thimerosal, and subsequently ethyl mercury, present in vaccines is not cytotoxic. A paucity of studies done specifically with thimerosal has led lawmakers to base regulations on the toxicological profile of methyl mercury. However, recent in vivo studies show a marked difference in the toxicological profiles of ethyl mercury, a metabolite of thimerosal, and methyl mercury. Neither in vitro nor in vivo studies, then, implicate thimerosal as a toxic agent at the concentrations present in vaccines. Epidemiological studies have been conducted in various countries assessing if a causal relationship exists between autism and thimerosal-containing vaccines. Though there is a concern that the ethyl mercury in thimerosal may cause neurotoxicity, which may lead to autism, large scale epidemiological studies have not been able to support this claim. In 2004, after critical review of major epidemiological studies, the Institute of Medicine’s Immunization Safety Committee released a report stating that a relationship between autism and mercury was not found. The media, however, (mainly small, local sources) have disproportionately covered stories supporting a link, taking advantage of the desperation felt by those personally affected by autism in order to increase sales. This, in turn, has caused many parents, especially parents of autistic children, to be hesitant to vaccinate their children. In order to address this, thimerosal was removed from all vaccines in the US market. While not justified in terms of reducing the risk of autism, the removal of thimerosal was justified in that it ensures that mislead parents will continue to vaccinate their children.