In a study that included approximately 95,000 children with older siblings it has been shown that receipt of the measles-mumps-rubella (MMR) vaccine was not associated with an increased risk of autism spectrum disorders (ASD), regardless of whether older siblings had ASD.  The data findings from the Lewin Group indicate no harmful association between receipt of MMR vaccine and ASD even among children already at higher risk for ASD, according to an opensource study published in the journal JAMA.

The team state that although a substantial body of research over the last 15 years has found no link between the MMR vaccine and ASD, a small population of parents and others continue to associate the vaccine with ASD. Surveys of parents who have children with ASD suggest that many believe the MMR vaccine was a contributing cause. This belief, combined with the knowledge that younger siblings of children with ASD are already at higher genetic risk for ASD, might prompt these parents to avoid vaccinating their younger children, according to the current study.

The team examined ASD occurrence by MMR vaccine status in a large sample of U.S. children who have older siblings with and without ASD. The researchers used an administrative claims database associated with a large commercial health plan. Participants included children continuously enrolled in the health plan from birth to at least 5 years of age during 2001-2012 who also had an older sibling continuously enrolled for at least 6 months between 1997 and 2012.

Of the 95,727 children included in the current study, 1,929 (2.01 percent) had an older sibling with ASD. Overall, 994 (1.04 percent) children in the cohort had ASD diagnosed during follow-up. Among those who had an older sibling with ASD, 134 were diagnosed with ASD, compared with the 860 children diagnosed with ASD whose siblings do not have ASD.

The MMR vaccination rate for the children with siblings without ASD in the current study was 84 percent (n = 78,564) at 2 years and 92 percent (n = 86,063) at age 5 years. In contrast, the MMR vaccination rates for children with older siblings with ASD were lower with 73 percent vaccinated at age 2 years and 86 percent vaccinated at age 5 years. Analysis of the data indicated that MMR vaccine receipt was not associated with an increased risk of ASD at any age.

Consistent with studies in other populations the researchers observed no association between MMR vaccination and increased ASD risk among privately insured children.  The team state that they also found no evidence that the receipt of either 1 or 2 doses of MMR vaccination was associated with an increased risk of ASD among children who had older siblings with ASD.

As the prevalence of diagnosed ASD increases, so does the number of children who have siblings diagnosed with ASD, a group of children who are particularly important as they were undervaccinated in the current study as well as in previous reports.

Source:  The JAMA Network Journals