http://www.medicalposting.ca/children/article.jsp?content=20040217_085151_4976&topStory=y Canadian says vaccine-autism study is overblown U.S. research linking preservative to brain disorders called wild over-extrapolation A Canadian researcher says a highly publicized U.S. study linking a mercury-containing vaccine preservative with autism and other brain disorders is no cause for worry. "It's probably one of the best examples of wild over-extrapolation in science I've ever seen," says Dr. Brian Ward, a vaccine immunologist at McGill University in Montreal. "At the very least they should be chided for overactive imaginations." In the study, a team led by Richard Deth, professor of pharmacology at Northeastern University in Boston, found that thimerosal -- a mercury-containing preservative used in some vaccines -- could interrupt biochemical reactions critical for brain development. Although the reactions were studied in special cells in a laboratory, the researchers say the concentrations of thimerosal were similar to those typically found following vaccination in humans. But according to Ward, the study does not show how thimerosal would actually affect cells in the body, nor is it clear how much of the preservative would make it into the brain. Furthermore, he says, the findings don't agree with population studies that have failed to show a link between vaccines and autism, attention deficit disorder and other neurological problems. Canada's National Advisory Committee on Immunization published a comprehensive review of thimerosal a year ago. The review points out few vaccines in Canada contain the preservative, and then only in trace amounts. "The risk that thimerosal or its metabolites may affect the neurologic development of infants is, at most, theoretical," the review states. "Because the risk of any health effect from thimerosal in vaccines has never been substantiated, and because, compared with the real risk of infection from inadvertent contamination of vaccine, the risk of thimerosal-related health effects is negligible. Vaccines containing thimerosal should not be withheld if they are needed." Still, the committee encouraged vaccine makers to develop alternatives to it. Thimerosal has been used to a much greater extent in vaccines made in the U.S., where it is also being phased out. In Canada, the preservative is used in vaccines that are distributed in multidose vials, such as influenza and hepatitis B. "This doesn't mean that the push to get thimerosal out of vaccines is an expression of communal guilt," says Ward, who is an associate professor of medicine and microbiology at McGill University and the Montreal General Hospital Research Institute.