Study Casts Doubt on Vaccine-Autism Link

The study authors pointed out that autism rates among kids aged 3 to 5 continued to grow for each birth year after 1999, even though thimerosal use dropped.

Shih said the study methods are "robust," adding that the authors appeared to address limitations of earlier studies. However, he said, the research "doesn't address the possibility that there might be a subpopulation who might be particularly vulnerable to a vaccine with thimerosal."

If just 1 percent to 2 percent of children were especially sensitive to the effect of thimerosal, the study wouldn't be able to pick it up, he said.

Schechter agreed, saying it was true that the research didn't address whether thimerosal might cause problems in a small number of cases.

As for a possible link between vaccines and autism, Shih said, "the jury is still out," especially considering that children are exposed to a large number of vaccines before age 2.

And he added, "Some people in the community feel that they might lead to immune problems that could either exacerbate or lead to autism. All this is purely hypothetical, but this is an area where we need to continue to do more research."

More information

To learn more about vaccines, visit the U.S. Centers for Disease Control and Prevention.

SOURCES: Robert Schechter, M.D., medical officer, Immunization Branch, California Department of Public Health, Richmond; Andy Shih, Ph.D., vice president, scientific affairs, Autism Speaks, New York City; January 2008,Archives of General Psychiatry