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Family history, MMR vaccine status do not affect autism occurrence

Receipt of measles-mumps-rubella vaccine was not associated with increased risk for autism spectrum disorders, regardless of whether older siblings had autism, according to study findings in JAMA.

“Although a substantial body of research over the last 15 years has found no link between the MMR vaccine and autism spectrum disorders (ASD), parents and others continue to associate the vaccine with ASD,” study researcher Anjali Jain, MD, of The Lewin Group, in Falls Church, Va., and colleagues wrote. “Parents cite vaccinations, especially MMR, as a cause of ASD and have deferred or refused vaccinations for their children as a result. Lower vaccination levels threaten public health by reducing both individual and herd immunity and have been associated with several recent outbreaks of measles.”

Researchers conducted a retrospective cohort study of privately insured children who had both medical and pharmacy coverage and were continuously enrolled in the health plan from birth to at least age 5 years. Study participants (n = 95,727) also had an older sibling continuously enrolled in the health plan for at least 6 months between 1997 and 2012.

Overall, 1.04% of study participants were diagnosed with ASD during the study period and 2.01% had an older sibling with ASD. Of those with an older sibling with ASD, 6.9% were diagnosed as well.

Eighty-four percent of children with unaffected older siblings received at least one dose of MMR at age 2 years and 92% at age 5 years. These rates were lower for children with siblings with ASD, at 73% at age 2 years and 86% at age 5 years.

Among children with unaffected siblings, unadjusted relative risk for ASD after at least one dose of MMR at age 2 years was 0.80 (95% CI, 0.44-1.47) vs. 0.44 (95% CI, 0.15-1.29) among children with affected siblings.

No association was found between one dose of MMR and ASD at ages 3, 4 and 5 years, regardless of older sibling ASD status.

For two doses of MMR at age 5 years, unadjusted relative risk for ASD was 0.74 (95% CI, 0.55-0.99) among children with unaffected siblings and 0.44 (95% CI, 0.26-0.75) among children with affected siblings.

In adjusted analysis, the relative risk for ASD after receipt of one dose of MMR at age 2 years was 0.91 (95% CI, 0.67-1.2) among children with unaffected siblings, compared with 0.76 (95% CI, 0.49-1.18) among children with affected siblings.

Further, for receipt of two doses of MMR at age 5 years, adjusted relative risk for ASD was 1.12 (95% CI, 0.78-1.59) among children with unaffected older siblings and 0.56 (95% CI, 0.31-1.01) among children with affected older siblings.

“In this large sample of privately insured children with older siblings, receipt of MMR vaccine was not associated with increased risk of ASD, regardless of whether older siblings had ASD,” Jain and colleagues wrote.

Interpretation of these study findings could lead to incorrect assumptions about receipt of MMR vaccine and risk for ASD, according to Bryan H. King, MD, MBA, of the University of Washington.

“Some parents of children with ASD may have chosen to delay immunization in subsequent children until they were certain any risk had passed. Such behavior, which arguably could enrich the immunization rate in the nonautism subgroup relative to the group that may have been showing early atypical development, might create the impression that MMR vaccine is actually reducing risk for ASD,” King wrote in an accompanying editorial. “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.” – by Amanda Oldt

Disclosure: Jain reports being an employee of The Lewin Group. King reports no relevant financial disclosures. Please see the full study for a list of all other authors’ relevant financial disclosures.