Thimerosal-containing vaccines and autistic spectrum disorder: a critical review of published original data.

Pediatrics. 2004 Sep;114(3):793-804. Related Articles, Links


Thimerosal-containing vaccines and autistic spectrum disorder: a critical
review of published original data.

Parker SK, Schwartz B, Todd J, Pickering LK.

Department of Pediatrics, Children's Hospital and University of Colorado
Health Sciences Center, Denver, Colorado 80262, USA.

OBJECTIVE: The issue of thimerosal-containing vaccines as a possible cause
of autistic spectrum disorders (ASD) and neurodevelopmental disorders (NDDs)
has been a controversial topic since 1999. Although most practitioners are
familiar with the controversy, many are not familiar with the type or
quality of evidence in published articles that have addressed this issue. To
assess the quality of evidence assessing a potential association between
thimerosal-containing vaccines and autism and evaluate whether that evidence
suggests accepting or rejecting the hypothesis, we systematically reviewed
published articles that report original data pertinent to the potential
association between thimerosal-containing vaccines and ASD/NDDs. METHODS:
Articles for analysis were identified in the National Library of Medicine's
Medline database using a PubMed search of the English-language literature
for articles published between 1966 and 2004, using keywords thimerosal,
thiomersal, mercury, methylmercury, or ethylmercury alone and combined with
keywords autistic disorder, autistic spectrum disorder, and
neurodevelopment. In addition, we used the "related links" option in PubMed
and reviewed the reference sections in the identified articles. All original
articles that evaluated an association between thimerosal-containing
vaccines and ASD/NDDs or pharmacokinetics of ethylmercury in vaccines were
included. RESULTS: Twelve publications that met the selection criteria were
identified by the literature search: 10 epidemiologic studies and 2
pharmacokinetic studies of ethylmercury. The design and quality of the
studies showed significant variation. The preponderance of epidemiologic
evidence does not support an association between thimerosal-containing
vaccines and ASD. Epidemiologic studies that support an association are of
poor quality and cannot be interpreted. Pharmacokinetic studies suggest that
the half-life of ethylmercury is significantly shorter when compared with
methylmercury. CONCLUSIONS: Studies do not demonstrate a link between
thimerosal-containing vaccines and ASD, and the pharmacokinetics of
ethylmercury make such an association less likely. Epidemiologic studies
that support a link demonstrated significant design flaws that invalidate
their conclusions. Evidence does not support a change in the standard of
practice with regard to administration of thimerosal-containing vaccines in
areas of the world where they are used.

PMID: 15342856 [PubMed - in process]