A study published in the September 27 issue of the New England Journal of Medicine (NEJM) found no consistent link between thimerosal, a mercury-containing preservative commonly used in childhood immunizations, and later neurological problems. The study examined more than 1,000 children between the ages of 7 and 10 years, and compared neuropsychological health and the level of thimerosal exposure in utero and during the first 7 months of life.

Thimerosal has been the focus of controversy for some time and was the subject of a recent post on baby gooroo®. Many parents of autistic children believe that their child’s autism was caused by thimerosal. It was widely used in all childhood vaccines prior to 1999, when the U.S. Food and Drug Administration (FDA) found that children immunized according to the recommended childhood immunization schedule could be exposed to excessive levels of mercury based on Environmental Protection Agency (EPA) tolerance levels.

Pending further investigation, the Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics (AAP) asked vaccine manufacturers to voluntarily eliminate or reduce the mercury content of vaccines—a decision experts feel fueled the controversy by suggesting a link in the absence of scientific evidence. Since 2003, all routinely recommended vaccines have been thimerosal-free with the exception of influenza vaccine.

The NEJM article adds to a growing body of evidence showing the safety of thimerosal. Nonetheless, parents of autistic children continue to believe that there is a causative link. Further investigation by the CDC is underway specifically targeting autistic children.