Exposure to thimerosal-containing vaccines in infancy or in the womb is not associated with an increased risk for developing autism, according to a new study from the CDC (Sep 2010).

It shows kids who had been exposed as babies to high levels of the preservative -- through vaccines they received or their mothers received while pregnant -- were no more likely to develop autism, including two distinct subtypes of the condition. 

The study is the latest of almost 20 studies to find no link between childhood vaccinations and autism.

The CDC researchers used data for U.S. children born between 1994 and 1999, who were enrolled in one of three managed care organizations. They found 256 children with an autism spectrum disorder and compared them with 752 children who did not have the condition, but were matched for age and sex.

No matter when a child had been exposed to thimerosal -- before birth when the mother had a shot, or when the child itself was vaccinated as a baby or toddler -- there was no increase in the risk of any type of autism spectrum disorder. In fact, the analysis indicated that children with the greatest exposures had slightly lower rates of autism than those who received fewer thimerosal-containing vaccines or none at all.

Concerns about a link between vaccines and autism were first raised more than a decade ago by British physician Andrew Wakefield. One widespread worry has been that thimerosal might play a role in the development of autism.

The study is very reassuring as the data show that you could receive a thimerosal vaccine and not be concerned about it. In the matter of fact, autism rates have continued to rise, although thimerosal has been removed from all routine childhood vaccines, except flu shots.