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Another nail in coffin of MMR-autism link

Even in children already at higher risk of autism, there’s no relative increase with MMR jab

Louise Prime

Thursday, 23 April 2015

Even among children already at higher risk of autism spectrum disorders (ASD), there is no further increase in risk associated with measles-mumps-rubella vaccination, researchers have reported* today in JAMA. The author of a linked editorial** said the study had confirmed that whether or not children have a sibling with autism, there is nothing to suggest a relationship between MMR and the development of autism.

Despite substantial evidence that there is no link between MMR and an increased risk of ASD, some parents of children with ASD continue to believe that the vaccine was at least a contributory cause; and because the relative risk of developing ASD is higher among siblings anyway, they can be reluctant to vaccinate their younger children against MMR. So US researchers set out to address this problem.

They investigated whether MMR vaccination was associated with any change in incidence of ASD among children who had, and didn’t have, an older sibling already diagnosed with ASD. They studied a cohort of 95,727 children, of whom 1,929 (2.01%) had an older sibling with autism, and 994 (1.04%) had ASD diagnosed during follow-up.

Of the children with an older sibling with ASD, 6.9% were themselves diagnosed with ASD, compared with just 0.9% of children with siblings without ASD. Among children with unaffected siblings, 84% had had at least one dose of MMR by 2 years old and 92% by 5 years old; among children with a sibling with ASD, vaccination rates were 73% and 86% respectively. The researchers found no indication that ASD risk at any age was associated with MMR vaccination.

They concluded: “Consistent with studies in other populations, we observed no association between MMR vaccination and increased ASD risk among privately insured children. We also found no evidence that 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 under-vaccinated in our observations as well as in previous reports.”

The author of an accompanying editorial commented: “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.

“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.”

* Anjali Jain, et al. Autism Occurrence by MMR Vaccine Status Among US Children With Older Siblings With and Without Autism. JAMA. 2015;313(15):1534-1540. doi:10.1001/jama.2015.3077
** Bryan H. King. Promising Forecast for Autism Spectrum Disorders. JAMA. 2015;313(15):1518-1519. doi:10.1001/jama.2015.2628

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