MONTREAL, July 5 ? As the mercury-containing preservative thimerosal was removed from vaccines, and as fewer children received the mumps-measles-rubella vaccine, the rates of autism and related disorders rose among Canadian school children.
In a study of nearly 28,000 children born between 1987 and 1998, the prevalence of pervasive developmental disorders was greater in those children vaccinated after the mercury-containing compound thimerosal was completely eliminated from vaccines in Canada, reported Eric Fombonne, M.D., of McGill University in Montreal, and colleagues.
Similarly, there was in increase in pervasive developmental disorders prevalence even as MMR vaccination rates declined, and the rate of increase remained constant even after a second dose of the vaccine was added to the recommended schedule, the investigators reported in the July issue of Pediatrics.
"In the past, concern about a potential link between MMR vaccinations and autism led some parents to take the drastic step of refusing to inoculate their children against dangerous childhood diseases like measles," Dr. Fombonne said. "This action resulted in resurgence of the measles, which caused the deaths of several young children in Europe. We hope this study will finally put to rest the pervasive belief linking vaccines with developmental diseases like autism."
In 2004, the Institute of Medicine committee on vaccine safety concluded that "the evidence favors rejection of a causal relationship between 1) thimerosal-containing vaccines and autism, and 2) MMR vaccine and autism."
Other studies have failed to find evidence of either a thimerosal- pervasive developmental disorders or MMR vaccine- pervasive developmental disorders link. For example, when thimerosal was removed from vaccines in Sweden and Denmark, there was no corresponding change in rates of autism reported in those countries.