Research Reaffirms: No Vaccine-Autism Link

A new study may be the latest nail in the coffin of a theory that draws a link between the mercury-containing vaccine additive thimerosal and autism.

The research is the latest to contradict concerns over childhood vaccinations as a possible cause of autism -- concerns that have gained publicity in the past decade as the number of children diagnosed with the disorder climbs steadily in the United States.

Because vaccinations are mandatory for all children at a certain age, some parents and doctors believe that the mercury once found in many childhood vaccines may contribute to the development of autism. However, so far a number of large scientific studies have shown no association between thimerosal and autism.

And the most recent research to nullify this association, published Monday in the journal Archives of General Psychiatry, reveals that the prevalence of autism for children ages 3 to 12 continued to increase in California even after 2001 -- when all but trace levels of mercury had been removed from most childhood vaccines.

"If thimerosal exposure is a primary cause of autism, then the prevalence of autism would be predicted to decrease, as young children's exposure to thimerosal has sharply decreased to its lowest levels in decades," noted lead study investigator Robert Schechter in the commentary section of the research.

Much Ado About an Additive

Before 2001, thimerosal was used in many childhood vaccines to prevent microbial contamination. However, in July 1999, the U.S. Public Health Service implemented a precautionary measure removing thimerosal -- which contains 49.6 percent ethylmercury -- from all childhood vaccines.

To determine whether reduced exposure to thimerosal led to a decrease in autism cases, researchers at the California Department of Public Health analyzed data from the California Department of Developmental Services on the prevalence by age and birth cohort of children with autism between 1995 and 2007.