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.