Safety of Thimerosal-Containing
Vaccines: Verstraeten
T, Davis R, DeStefano F, Lieu T, Rhodes P, Black S, Shinefield H, Chen
R Abstract: Pediatrics 2003 112(5):1039-1048 Findings There is ongoing concern and controversy about children who receiving vaccines that contain thimerosal, an organic preservative containing 49% mercury. Information about the effects of parenteral exposure to these compounds in humans is limited to a few case reports, none of which involved exposure from vaccines. Vaccines, however, constitute a nearly universal exposure for children in the United States and most other countries. To evaluate the theoretical concerns of the potentially toxic effects of thimerosal in vaccines, Dr. Verstraeten and his colleagues studied neurodevelopmental outcomes among a large group of children with documented exposure to varying levels of thimerosal from vaccinations in several health maintenance organizations (HMOs). In phase I of the study, the authors screened for potential associations between thimerosal-containing vaccines and neurological disorders in 124,170 infants born between 1992-1999 at 2 HMOs; in phase II of the study, the most common disorders associated with exposure in phase I were re-evaluated in 16,717 children who were born during 1991-1997 in another HMO. In phase I at one HMO, cumulative exposure at 3 months resulted in a significant positive association with tics (a condition in which a part of the body moves repeatedly, quickly, suddenly and uncontrollably). At the second HMO B, increased risks of language delay were found for cumulative exposure at 3 months and 7 months. In phase II at the third HMO, no significant associations were found. In no analyses were significant increased risks found for autism or attention-deficit disorder. Conclusions This study found no consistent significant associations between thimerosal-containing vaccines and neurodevelopmental outcomes. Conflicting results were found at different HMOs for certain outcomes. However, in the independent population of children, the associations seen in Phase I could not be repeated and this lack of consistency argues against an associationsThe authors suggest, for resolving these conflicting findings, studies with uniform neurodevelopmental assessments of children with a range of cumulative thimerosal exposures are needed.
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