In the latest study on the vaccines, researchers find even more evidence that childhood immunizations aren’t linked to autism.

In a study published in the Journal of the American Medical Association, a group led by Dr. Anjali Jain of the Lewin Group, a health care consulting organization, found that brothers and sisters of children with autism were not at any higher risk of developing the disorder if they were vaccinated compared with brothers and sisters of those without autism.

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Numerous studies have found an increased risk of autism among those with older siblings with the condition, and some parents who believe that their older child’s autism is connected to vaccinations, specifically the MMR vaccine, have been reluctant to immunize their younger children. Indeed, Jain found that vaccination rates among siblings of autistic children were lower, at about 86% at 5 years, compared with 92% among those without autistic brothers or sisters.

But among the 95,000 children with older siblings included in the study, children who received the MMR and had autistic older siblings were no more likely to develop autism than children who were vaccinated and didn’t have any autistic older siblings. In fact, the relative risk of autism among those with older autistic brothers or sisters was lower if they were vaccinated compared with those who were not vaccinated.

“Our study confirmed that in kids with older siblings who we know are at increased risk of developing autism themselves, those kids are being vaccinated less,” says Jain. “But in the kids who did develop autism who were vaccinated, there was no increased risk from the vaccine compared to kids who did not get the vaccine.”

The results, she says, should put to rest any concerns that parents of autistic children might have that vaccinating their younger kids will somehow increase their risk of developing autism. The large size of the study, and the fact that vaccination and autism information wasn’t collected for purposes of a vaccines-and-autism study but as part of a larger health insurance database, also reinforce the strength of the findings. (The Lewin Group is an editorially independent part of Optum company, which collected the data.)

“We may not understand what is causing autism in these kids or families,” says Jain. “There could be a host of both genetic and environmental factors. But we are able to look at the vaccines themselves and show there is no association with autism.”

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