There is no link between autism and vaccines containing the preservative thimerosal, another new study has found.
The results show that children exposed to the once-questioned chemical thimerosal, either in the womb or as infants, are not at increased risk for autism .
The findings agree with those of previous research, including a large 2008 study that found no link between the measles, mumps and rubella (MMR) vaccine and autism cases.
The idea that a connection existed between autism and vaccines was proposed by researcher Andrew Wakefield in a 1998 study in the journal The Lancet. The study was widely discredited and has since been retracted.
Thimerosal is a vaccine preservative that contains mercury and has been used since the 1930s. In 1999, the U.S. Food and Drug Administration estimated that infants who were immunized according to the recommended schedule might have received amounts of ethylmercury, a byproduct of thimerosal, that exceeded the Environmental Protection Agency limits for exposure to methylmercury.
As a precautionary measure, the U.S. Public Health Service and the American Academy of Pediatrics urged vaccine manufacturers to remove thimerosal from all infant vaccines as soon as practical and recommended that studies be conducted to investigate the risks associated with exposure to thimerosal-containing vaccines, the researchers say.
The current study involved 256 children diagnosed with an autism spectrum disorder, including autism and milder psychological conditions affecting social and behavioral skills. The study also included 752 children who did not have an autism spectrum disorder, but were similar in age and gender.
The researchers looked at immunization registries, medical charts and also spoke with parents to determine whether the children had been exposed to thimerosal in the womb or after birth, up to 20 months old.
There was no relationship between thimerosal exposure and diagnosis with autism, the researchers say.
The study was published in the October issue of the journal Pediatrics.