Prenatal and infant exposure to thimerosal, a mercury-containing preservative used in some vaccines, does not increase risk for autism spectrum disorder (ASD), according to a study published in the October 2010 print issue of Pediatrics.
In the study, researchers tasked by the US Centers for Disease Control reviewed health records and conducted interviews with the parents of 256 children diagnosed with ASD. Children with ASD were further categorized as having autistic disorder or ASD with regression (meaning children with autism who lost previously acquired language skills). Another 752 children without autism, matched to the ASD children by birth year and gender, were also studied.
Researchers compared thimersol exposures during the following time periods: prenatal, birth to 1 month, birth to 7 months, and birth to 20 months. Confirming previous vaccine safety studies, researchers found no connection between thimerosal exposure and increased risk for ASD in any of the time periods. In an unexpected anomaly, the study noted that, in fact, the number of ASD cases decreased with increasing thimerosal exposure in the birth to 7 months and birth to 20 months time periods.
According to the CDC, an average of one in 110 children in the US have some form of autism and boys are four to five times more likely to have autism than girls. And as a report released in early 2010 showed, as many as one in four parents fear routine vaccinations raise the likelihood for a child to develop autism. Researchers hope their findings help to quell the concerns of skeptical parents.
"This study adds to the evidence that thimerosal-containing vaccines do not increase a child's risk of developing autism," says lead study author, Dr. Frank DeStefano of the Centers for Disease Control, in an interview with CNN.