Pharmacists are often confronted with parents who refuse to vaccinate their children because of concerns about autism. Now, they can respond with the latest data.

A nationwide cohort study of all children born in Denmark to Danish-born mothers between 1999 through 2010 concluded that the mumps, measles, and rubella (MMR) vaccine does not increase the risk of autism. In fact, the research published in Annals of Internal Medicine determined that vaccines don’t even trigger autism in susceptible children nor is the MMR associated with clustering of autism cases following vaccination.

For the study, researchers from Statens Serum Institut in Copenhagen used a Danish population registry to analyze whether the MMR vaccine increases the risk for autism in children, subgroups of children, or time periods after vaccination. The study linked information on MMR vaccination, autism diagnoses, other childhood vaccines, sibling history of autism, and autism risk factors to the 657,461 children in the cohort.

The study team reports that during more than five million person-years of follow-up, 6,517 children were diagnosed with autism (incidence rate, 129.7 per 100 000 person-years). When MMR-vaccinated children were compared with MMR-unvaccinated children, a fully adjusted autism hazard ratio of 0.93 (95% CI, 0.85-1.02) resulted. In addition, no increased risk for autism after MMR vaccination was consistently observed in subgroups of children defined according to sibling history of autism, autism risk factors (based on a disease risk score) or other childhood vaccinations, or during specified time periods after vaccination.

“The study strongly supports that MMR vaccination does not increase the risk for autism, does not trigger autism in susceptible children, and is not associated with clustering of autism cases after vaccination,” study authors conclude. “It adds to previous studies through significant additional statistical power and by addressing hypotheses of susceptible subgroups and clustering of cases.”

“In this study, we aimed to evaluate the association again in a more recent and nonoverlapping cohort of Danish children that has greater statistical power owing to more children, more cases, and longer follow-up,” the researchers add. “A criticism of our and other previous observational studies has been that these did not address the concern that MMR vaccination could trigger autism in specific groups of presumably susceptible children, in contrast to all children; the current study addresses this concern in detail.”

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