In the largest-ever study of its kind, researchers again found that the measles-mumps-rubella (MMR) vaccine did not increase risk for autism spectrum disorder (ASD). This proved true even among children already considered at high risk for the disorder.
In all, the researchers analyzed the health records of 95,727 children, including more than 15,000 children unvaccinated at age 2 and more than 8,000 still unvaccinated at age 5. Nearly 2,000 of these children were considered at risk for autism because they were born into families that already had a child with the disorder.
The report appears today in JAMA, the Journal of the American Medical Association.
“Consistent with studies in other populations, we observed no association between MMR vaccination and increased ASD risk,” the authors write. “We also found no evidence that receipt of either one or two doses of MMR vaccination was associated with an increased risk of ASD among children who had older siblings with ASD.”
The analysis looked at autism rates and MMR vaccination at ages 2, 3, 4 and 5 years. It showed no increased risk of autism with immunization at any age. In fact, autism rates were lower in the vaccinated groups. However, this might be because parents who see early signs of autism were more likely to delay or avoid vaccination, the authors speculate.
Lower vaccination rates among families affected by autism
Some 15 year ago, a small, now-discredited study sparked concerns about a link between the MMR vaccine and autism. Since then, a large and growing body of research has continued to find no association. Still, the continuing uncertainty around what does cause autism has left some people worried. Such concerns likely explain why vaccination rates have dropped in families that have an older child with the disorder.
In the new study, MMR vaccination rates for children without an affected older siblings were 84 percent at 2 years and 92 percent by age 5 years. Vaccination rates for children with an older sibling affected by autism were significantly lower: 73 percent at 2 years and 86 percent at age 5 years.
In an accompanying editorial, Dr. Bryan King, director of the Seattle Children’s Autism Center, writes:
“Taken together, some dozen studies have now shown 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.”
Study made possible by large database
The investigators performed their analysis using the claims records from a large US health plan database (the Optum Research Database). Participants included children continuously enrolled in an associated health plan from birth to at least 5 years of age between 2001 and 2012. All had an older sibling.
Of the 95,727 children in the study, around 1 percent (994) were diagnosed with autism during the study’s follow-up period. Among those who had an older sibling with autism (1,929), approximately 7 percent (134) developed the disorder. This difference in autism prevalence – between children with or without an older sibling affected by autism – is consistent with earlier studies.