Vaccination With MMR Does Not Increase Autism Risk

Vaccination against measles, mumps, and rubella (MMR) does not increase the risk for autism or trigger autism in susceptible children, according to a new cohort study published in the March 5 issue of Annals of Internal Medicine.

"[Our study] is by far the largest single study to date and adds significantly to our knowledge on the issue, in that it allows us to conclude from one study that even minute increases in autism risk after MMR vaccination are unlikely, assuming unbiased results," write Anders Hviid, DrMedSci, from the Statens Serum Institut in Denmark, and colleagues.

The researchers reviewed medical records from 657,461 children born between January 1, 1999 and December 31, 2010. All included children received two doses of MMR vaccine; no vaccines contained thimerosal. All children were followed from January 1, 2000 through August 31, 2013 resulting in 5,025,754 person-years of follow-up. Information on diagnosis of autism spectrum disorder (ASD) included autistic disorder, Asperger syndrome, atypical autism, other pervasive developmental disorder, and unspecified pervasive developmental disorder.

The researchers found that 6517 children were diagnosed with autism during the study period, resulting in an incidence rate of 129.7 per 100,000 person-years. The overall uptake of the first dose of MMR vaccine was 95.19% and the median age at the time of vaccination was 1.34 years.

As part of their analysis, Hviid and colleagues also determined patient risk for autism, including conditions such as fragile X syndrome, tuberous sclerosis, Angelman syndrome, Down syndrome, DiGeorge syndrome, neurofibromatosis, Präder–Willi syndrome, and congenital rubella syndrome. Maternal age, paternal age, smoking during pregnancy, method of delivery, preterm birth, 5-minute Apgar score, low birthweight, and head circumference were also considered in the risk factor assessment.

Comparing MMR-vaccinated children and MMR-unvaccinated children yielded a fully adjusted autism hazard ratio (aHR) of 0.93 (95% confidence interval [CI], 0.85 – 1.02).

When the cohort was categorized into subgroups characterized by sex, birth cohort, other vaccines received, autism risk score, or history of siblings with autism, MMR vaccination "did not increase the risk for autism in children characterized by other early childhood vaccinations, high risk for autism, or having autistic siblings," the researchers write.

The study authors also evaluated hazard ratios in 1-year risk periods following MMR vaccination and noted no increase in aHRs during any period.

In an accompanying editorial, Saad B. Omer, MD, PhD, and Inci Yildirim, MD, PhD, both from Emory University, Atlanta, Georgia, agree these results are important and support previous findings that MMR vaccination poses no increased risk for autism.

Omer and Yildirim question, however, whether there is a need for more studies refuting this link and posit that even "the discussion around the potential link has contributed to vaccine hesitancy."

"Therefore, generating evidence on MMR vaccine safety may be useful but is certainly not sufficient," they write. Omer and Yildirim go on to suggest that "while confronting the erroneous information, the focus should be on a few key facts; it is not essential to rebut every piece of misinformation."

Funding for this study was provided by the Novo Nordisk Foundation and the Danish Ministry of Health. Hviid and a coauthor have received grants from Novo Nordisk Foundation. The remaining authors and editorialists have disclosed no relevant financial relationships.

Ann Intern Med. Published March 5, 2019. March 5, 2019. Abstract, Editorial

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