The mumps, measles, and rubella (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, according to a nationwide cohort study from Denmark.
In 1998, The Lancet published a controversial paper in which a group of researchers from the Royal Free Hospital and School of Medicine London reported on 12 children with developmental delay, eight of whom were diagnosed with autism within four weeks of receiving the MMR vaccine.
Despite the small sample size, the uncontrolled design, and the speculative nature of the conclusions, the later retracted paper received wide publicity, and the hypothesized link between the vaccine and autism continues to cause concern and challenge vaccine uptake.
In 2002, a research team led by scientists from Denmark’s Statens Serum Institut addressed this issue in a nationwide cohort study of 537,303 Danish children with 738 cases of autism. MMR vaccination was not associated with autistic disorder or other autism spectrum disorders.
In the new study, the team aimed to evaluate the association again in a more recent and non-overlapping cohort of Danish children that has greater statistical power owing to more children, more cases, and longer follow-up.
Of the 657,461 children included in the analysis over a decade of follow-up, 6,517 were diagnosed with autism.
Comparing MMR-vaccinated with MMR-unvaccinated children yielded a fully adjusted autism hazard ratio of 0.93.
Similarly, 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.
“Our study does not support that MMR vaccination increases the risk for autism, triggers autism in susceptible children, or is associated with clustering of autism cases after vaccination,” the study authors said.
“It adds to previous studies through significant additional statistical power and addresses questions about susceptible subgroups and autism clustering.”
The findings were published in the Annals of Internal Medicine.
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Anders Hviid et al. Measles, Mumps, Rubella Vaccination and Autism: A Nationwide Cohort Study. Ann Intern Med, published online March 5, 2019; doi: 10.7326/M18-2101