Study Again Confirms No Link Between MMR Vaccine and Autism

Once again, a large study of Danish residents confirmed that the measles, mumps, rubella (MMR) vaccine is not associated with an increase in autism and does not trigger autism in children who are susceptible to the disorder. Findings from this study were published in the Annals of Internal Medicine.¹

Researchers obtained data of children born in Denmark between January 1, 1999, and December 31, 2010, including data on vaccinations and autism diagnoses. Specifically, the researchers examined rates and associations between the MMR vaccine and autism diagnoses, other childhood vaccines, sibling history of autism, and autism risk factors. The final cohort consisted of 657,461 children (mean age, 8.64 years), represented by 5,025,754 person-years of follow-up. Analyses for the association between MMR vaccination and receiving an autism diagnosis were adjusted for age, birth year, sex, other childhood vaccines, sibling history of autism, and autism risk factors.

A total of 6517 children in the sample were diagnosed with autism (mean age at first autism diagnosis, 7.22 years) during the follow-up period (incidence rate, 129.7 per 100,000 person-years). The median age at time of MMR vaccination was 1.34 years, and the uptake of the vaccine was 95.19%. No difference was found between MMR-vaccinated children and those not vaccinated with MMR in terms of receiving an autism diagnosis, as determined by a fully adjusted hazard ratio (aHR) of 0.93 (95% CI, 0.85-1.02).

In a subgroup analysis, receipt of the MMR vaccine was associated with reduced autism risk in girls (aHR, 0.79; 95% CI, 0.64-0.97) as well as in the entire 1999 through 2001 cohort (aHR, 0.84; 95% CI, 0.73-0.96). Risk factors associated with a higher risk for autism included being a boy (HR, 4.02; 95% CI, 3.78-4.28), being born in a late birth cohort (2008-2010; HR, 1.34; 95% CI, 1.18-1.52), having no early childhood vaccinations (HR, 1.17; 95% CI, 0.98-1.38), and having siblings with autism at study entry (HR, 7.32; 95% CI, 5.29-10.12).

Limitations of the study include the lack of individual medical chart review as well as the inclusion of only Danish children born to Danish mothers, which may limit generalizability.

In an accompanying editorial, Saad B. Omer, MBBS, MD, PhD, and Inci Yildirim, MD, PhD, MSc, suggested that the myth linking the MMR vaccine with autism should be dispelled by practitioners by engaging with patients and their families using simple evidence-based education. “While confronting the erroneous information, the focus should be on a few key facts; it is not essential to rebut every piece of misinformation,” the researchers wrote.² “Finally, an alternative explanation of the perceived phenomenon should be provided. Otherwise, the individual can revert to their original erroneous belief.”

References

1. Hviid A, Hansen JV, Frisch M, Melbye M. Measles, mumps, rubella vaccination and autism: a nationwide cohort study [published online March 5, 2019]. Ann Intern Med. doi: 10.7326/M18-2101.
2. Omer SB, Yildirim I. Further evidence of MMR vaccine safety: scientific and communications considerations [published online March 5, 2019]. Ann Intern Med. doi: 10.7326/M19-0596.