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AN INVESTIGATION INTO THE SUPPOSED LINK BETWEEN THIMEROSAL-CONTAINING VACCINES AND AUTISM RUPALI AVASARE, CHRISTINA FUENTES, LYNN NGO BE.104—May 10, 2005 Abstract 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. 1
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Autism is a neurological disorder that is characterized by deficits in verbal and nonverbal communication, social interaction, and repetitive behaviors or interests. Autism technically consists of five disorders with varying severity—termed autism spectrum disorders—and is now estimated to affect as many as one in every 166 children. While research continues to investigate this disorder, which was first identified in 1943, as of now there are no known causes of autism and no consistent finding as to the changes that occur in the brains of autistic patients. Because of this, diagnosing and treating autism are challenging endeavors. 1 The Food and Drug Administration (FDA) Modernization Act of 1997 prompted a review of mercury-containing drugs by the FDA. This review lead to a concern for the usage of thimerosal-containing vaccines, revealing that certain vaccines used since 1991 contained ethyl mercury levels that, for a six-month-old infant, were higher than the Environmental Protection
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This note was uploaded on 11/11/2011 for the course BIO 20.010j taught by Professor Lindagriffith during the Spring '06 term at MIT.

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