A new study has yielded more evidence that there is no link between the childhood measles-mumps-rubella vaccine and an increased risk of autism, even in children with a genetic risk of developing it, researchers say.
Receiving the MMR vaccine was not tied to a risk of developing autism even in children with older siblings diagnosed with the condition, they say.
Since the claim of a link was first raised in a small study in 1998 — a study since retracted amid charges of fraud — numerous studies have been in agreement in finding no such associations.
Vaccination records and health data on more than 95,000 children with older siblings, some of whom had autism spectrum disorder (ASD) were analyzed for the latest study, researchers reported in the Journal of the American Medical Association.
The study was undertaken because "despite the research that shows no link between the MMR vaccine [and autism], parents continue to believe that the vaccine is contributing to autism," says Dr. Anjali Jain, a study author who is with health care consulting firm The Lewin Group, based in Falls Church, Virginia.
"Parents who already have a child with autism seem especially prone to this belief," Jain added.
This was borne out by a study finding that children with older siblings diagnosed with autism were less likely to have been vaccinated than those in a family with no signs of autism, the researchers said.
Despite all the studies finding no link between the MMR vaccine and autism, some parents still believe in an association, says Dr. Thomas Frazier, head of the Cleveland Clinic Center for Autism, who was not involved in the most recent study.
"Unfortunately, it is a psychological problem; it is not a data problem," Frazier says. "So we could probably do a hundred more of these studies, and you would not actually change parents' behavior."
While the new study may not settle the debate, its data — and its message — are clear, Bryan King of the University of Washington wrote in an editorial accompanying the publication of the results.
"The only conclusion that can be drawn from the study is that there is no signal to suggest a relationship between MMR and the development of autism in children with or without a sibling who has autism," King wrote.
He cited at least a dozen studies showing the time of onset of autism spectrum disorder does not differ between vaccinated and unvaccinated children, nor does its severity or course differ between children who have been vaccinated and those who have not been.
"And now, the latest study shows the risk of ASD recurrence [in younger siblings] in families does not differ between vaccinated and unvaccinated children."