least a dozen major studies have found that early childhood vaccines do not cause autism. But one possibility remained: that immunizations could cause autism in a small group of children who were already primed to develop the disorder.
Now, new research has ruled out that possibility too.
A study of nearly 100,000 children found that toddlers known to have an elevated risk of autism were no more likely to be diagnosed with the disorder if they were vaccinated against measles, mumps and rubella than if they weren’t. What’s more, the diagnosis rate for high-risk children who were vaccinated was the same as for immunized children with no family history of the disorder, according to the report published Tuesday in the Journal of the American Medical Assn.
By hunting for — and failing to find — a link between the MMR vaccine and autism spectrum disorders, or ASD, in children with an older sibling who had the disease, the study leaves no doubt that the two are not connected, experts said.
While “abundant” evidence demonstrates that the MMR vaccine does not lead to ASD in the general population, it was still worth investigating whether there might be a connection among the more vulnerable population of kids with an older sibling on the autism spectrum, said Dr. Bryan H. King, an autism specialist at Seattle Children’s Hospital who was not involved in the new research.
“Could it be that if all the requisite genetic and other risks are present, MMR can lead to the development of autism?” King asked in an editorial published alongside the JAMA study. “If so, the population in which there might be such a signal would be families already affected by autism.”
By showing such fears to be unfounded, the study — and others before it — makes plain that “the age of onset of ASD does not differ between vaccinated and unvaccinated children, the severity or course of ASD does not differ between vaccinated and unvaccinated children, and now the risk of ASD recurrence in families does not differ between vaccinated and unvaccinated children,” he said.
But the vocal minority of parents who contend that there is a cause-and-effect relationship between the MMR vaccine and autism aren’t likely to be swayed, said Dr. James Cherry, a pediatric infectious disease specialist at UCLA who wasn’t involved in the new research.
“Eight million studies are not going to convince people,” he said.
Autism is a neurological disorder that has become more common in recent years, though scientists don’t know why. In 2002, ASD affected about 1 in 150 children in the U.S., according to the Centers for Disease Control and Prevention; by 2010, the prevalence had risen to about 1 in 68.
Symptoms can be relatively mild, as in the social difficulties of people with Asperger’s syndrome, or they can be so debilitating that individuals, as adults, can’t live on their own.
The idea that vaccines cause autism goes back to a 1998 study in the medical journal Lancet that described 12 young children with autism-like symptoms. Eight of those children started having behavioral problems after they got the MMR vaccine, according to their parents.
That study was retracted in 2010 after its lead author, Dr. Andrew Wakefield, was found to have falsified his research. Yet his claims continue to stoke the anti-vaccination movement.
