Thimerosal-Containing Vaccines and Autistic Spectrum Disorder: A Critical Review of Published Original Data. Parker SK, Schwartz B, Todd J, and Pickering LK. Pediatrics 2004;114:793-804.
What is the quality of the evidence assessing a link between thimerosal-containing vaccines (TCV) and neurodevelopmental disorders (NDD), including autism and autism spectrum disorders (ASD)?
This study sought to identify—from the National Library of Medicine’s Medline database (PubMed) and the Cochrane Library—all research publications reporting original data that were published between 1966 and 2004 that examined 1) for an association of TCV and autism, ASD, or NDD and 2) the human pharmokinetics (the accumulation and elimination from the body) of ethylmercury, the potential toxin in thimerosal.
The authors then evaluated each publication for the study design, the methods used, the types of analyses performed, and what interpretations could be made from the studies.
The authors identified 14 published studies, 10 epidemiologic and 4 pharmacokinetic. Each publication was critically reviewed.
The quality of the reviewed articles varied significantly:
Of the published literature identified by this study, the majority of the epidemiological studies did not demonstrate an association between TCV and autism. A small number of epidemiological studies suggesting an association were found to be of poor quality with methodological flaws that made interpretation impossible.
What little data there are about the pharmacokinetics of thimerosal also suggest that an association is less likely.
The findings from an increasing number of studies should provide reassurance that there continues to be no evidence of an association between autism, ASD, or NDD and TCV. Many of the studies reviewed in this article have also been reviewed on this Web site.