Receipt of the measles-mumps-rubella (MMR) vaccine was not associated with increased risk of autism spectrum disorders (ASD), even for children who had an older sibling with autism, according to a study of nearly 100,000 children, published in JAMA.
According to the findings, of 95,727 children with older siblings, 994 (1.04%) were diagnosed with ASD and 1929 (2.01%) had an older sibling with ASD. Of those with older siblings with ASD, 134 (6.9%) had ASD, vs 860 (0.9%) children with unaffected siblings (P?<?.001).
MMR vaccination rates (?1 dose) were 84% (n?=?78?564) at age 2 years and 92% (n?=?86?063) at age 5 years for children with unaffected older siblings, vs 73% (n?=?1409) at age 2 years and 86% (n?=?1660) at age 5 years for children with affected siblings.
MMR vaccine receipt was not associated with an increased risk of ASD at any age. For children with older siblings with ASD, at age 2, the adjusted relative risk (RR) of ASD for 1 dose of MMR vaccine vs no vaccine was 0.76, and at age 5, the RR of ASD for 2 doses compared with no vaccine was 0.56.
For children whose older siblings did not have ASD, at age 2, the adjusted RR of ASD for 1 dose was 0.91 and at age 5, the RR of ASD for 2 doses was 1.12.
“These findings indicate no harmful association between MMR vaccine receipt and ASD even among children already at higher risk for ASD,” the researchers concluded.
“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,” Dr Anjali Jain of the Lewin Group, said in an interview with TIME. “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.”
Jain and the research team hope the results will help refute beliefs that vaccines such as MMR cause autism, beliefs that lead to lower vaccination levels.
“We may not understand what is causing autism in these kids or families,” Jain told TIME. “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.”