Latest Study Fails to Find Thimerosal-Autism Link
A government-funded study on thimerosal-containing vaccines and immunoglobulin preparations has failed to find a link between the mercury-based preservative and the risk of autism spectrum disorder (ASD). The research, published online in the journal Pediatrics, “should reassure parents about following the recommended immunization schedule,” says Dr. Frank Destefano of the US Centers for Disease Control and Prevention.
Thimerosal Has Been Removed from Most Childhood Vaccines
Thimerosal is a mercury-containing organic compound that has been used as a preservative in a number of biological and drug products since the 1930’s, according to the US Food and Drug Administration. The product is used to help prevent potentially life-threatening contamination from harmful microbes. However, due to a concern about mercury toxicity, thimerosal has been removed from or reduced to trace amounts in all vaccines routinely recommended for children 6 years of age or younger with the exception of inactivated influenza vaccine.
Mercury-containing vaccines have been debated over the past decade when a small study by Dr. Andrew Wakefield warned that certain preventative vaccines, particularly the MMR vaccine, was linked to autism spectrum disorder. The study has recently been retracted by The Lancet, where it originally appeared, and Dr. Wakefield has lost his medical license.
Because the cause of the recent rise of autism spectrum disorders among children cannot yet be pinpointed, research continues into thimerosal to prove or disprove its safety.
Dr. Frank Destefano, director of the Immunization Safety Office at the CDC and the study's senior author, and colleagues including Cristofer S. Price of Abt Associates in Cambridge MA conducted a case-control study between 1994 and 1999 that included 256 children with ASD and 752 matched controls. The team gathered immunization records for the children and their mothers and compiled a thimerosal exposure level “score”.
The researchers found no link between vaccinations, whether prenatally or after birth, and the development of autism. In fact, those kids who were exposed to the preservative between birth and 20 months of age had slightly lower odds of developing the condition, although the researchers could not explain that result.
DeStefano and colleagues did identify several limitations of their own study: the possibility of unmeasured confounding factors, potential recall and reporting bias in the maternal interviews, and the uncertainty inherent in diagnoses of autism spectrum disorders.
Price C, et al "Prenatal and infant exposure to thimerosal from vaccines and immunoglobulins and risk of autism" Pediatrics 2010; 126: 656-64.