May 18, 2004 -- An expert panel says conclusively that the mercury-containing vaccine preservative thimerosal does not cause autism in children. But a national, parent-led vaccine reform group says the panel is practicing politics, not medicine.
The expert panel, convened by the Institute of Medicine, also concludes in a report that the common measles, mumps, and rubella combination vaccine, also called MMR, does not cause autism as some have suspected.
"The evidence favors a rejection of a causal relationship of thimerosal-containing vaccines and autism," says Marie McCormick, MD, professor of maternal and child health at the Harvard School of Public Health and the panel's chairwoman. McCormick says the 13-member committee was unanimous in its conclusions.
Thimerosal was used for decades to prevent bacterial contamination in many different vaccines. The chemical is a mercury-based preservative with the potential to cause neurological and developmental problems.
Under mounting pressure from the public and Congress, companies began removing thimerosal from vaccines in 1999. Now all universally recommended childhood vaccines are available with no thimerosal.
Tuesday's conclusions are the last of a years-long review of vaccine safety by the committee elected by the Institute of Medicine. They appear to put a period on a long-running debate raging among families, scientists, and in the courts over whether thimerosal or individual vaccines are responsible for the alarming rise in childhood autism cases since 1990.
A 2001 report from the same committee concluded that there was "inadequate" evidence to accept or reject a link between thimerosal and neurological disorders including autism and attention deficit hyperactivity disorder.
Experts said that several studies released since 2001 convinced them to reject the link. Five published studies "are consistent in providing no link," McCormick says.
At the same time, 14 studies have concluded that the MMR vaccine does not lead to autism in vaccinated children. Two studies found an association, though the committee said that researchers used poor methods in their study design and the study was of poor quality.
"The weight of that evidence is pretty substantial since all of the studies go in the same direction," McCormick says.
The conclusions anger vaccine activists who have been fighting to expose what they see as evidence that multiple childhood vaccinations are dangerous for children.
Barbara Loe Fisher, president of the watchdog group the National Vaccine Information Center, says she is "stunned" by the committee recommendation that researchers discontinue active study of vaccines and autism and look instead at possible genetic factors in overall mercury metabolism.
"They're saying that the case is closed," Fisher tells WebMD. She suggests that the panel was acting to protect large government research grants at their home universities.
"This is extremely political, not scientific," she says.
Vaccines Still Recommended
Despite the findings, experts recommend that children under 6 receive thimerosal-free vaccines. "This is a precautionary measure to reduce the exposure to mercury from all sources. In terms of autism, vaccines do not represent the risk," McCormick says.
Experts note that not vaccinating children against diseases can be dangerous.
"The risks of the diseases that are being prevented with these vaccines are very, very real," says Steven Goodman, MD, associate professor of oncology and epidemiology at the Johns Hopkins School of Medicine and a member of the panel.