A comprehensive examination of 50 years of research on the combined vaccine for measles, mumps and rubella has concluded parents' fears the shots could give their children autism or bowel disease are unfounded.
Experts say the study, together with other recent authoritative reviews, show definitively there is no evidence of a connection between the inoculations and developmental and bowel problems in children, and that parents should be reassured the shots are safe.
However, parents who believe their children have been harmed by the vaccine, known as MMR, were not convinced.
Several groups, including the World Health Organization, the U.S. Institute of Medicine, and Britain's Medical Research Council have reviewed evidence investigating a possible link between the vaccine and autism, but the latest project, published Tuesday in the Internet version of the journal Clinical Evidence, is the most comprehensive.
"We looked through over 2,000 studies on millions of children, covering 50 years of research,'' said lead investigator Dr. Anna Donald, whose company, Bazian Ltd., analyzes the quality of medical research and was contracted by the publishing arm of the British Medical Association to conduct the review.
"The science is very rigorous and this really does give a green light to MMR,'' she said. "The science on this issue is over; the scientific debate is dead.''
However, Ann Coote from Jabs, a British-based support group for parents who believe their children have been damaged by the MMR vaccine, said she believes the issue has not been settled.
"It's not new evidence. It's only old evidence rehashed,'' she said. "That's what's annoying parents _ if we've got all this money to throw away on keeping on reviewing things, haven't we got the money to start new research and look into it once and for all?''
Fears over the MMR vaccine intensified in 1998 after a British study raised the possibility of a connection between the vaccine and developmental problems in 12 children with bowel ailments. The study was conducted about eight years after the children had been vaccinated.
By February of this year, MMR immunization in British 2-year-olds had dropped to 84 percent, well below the 95 percent specialists say is needed to prevent measles returning. The decline prompted the British health authorities to launch a campaign to persuade parents the vaccine is safe.
Donald said there is no doubt more research on autism is needed, but she would not endorse any more research into the link between autism and MMR.
"This is a terrible distraction from limited funds that need to be looking at autism itself and not at something that has been answered more convincingly than most things we have ever tried to look at,'' she said.
Dr. John Clemens, a medical officer in the immunization program at the World Health Organization, said WHO will continue to monitor future vaccine safety studies but the U.N. health agency sees no need to spend more money to further investigate a link to autism.
Dr. Neal Halsey, director of the Institute for Vaccine Safety at Johns Hopkins University, said scientists should try to determine whether measles viruses linger in the intestines or other tissues, but the outcome of such studies would not alter his opinion that MMR is safe and effective.
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