Summary: A large new nationwide study finds no evidence that the measles, mumps, and rubella (MMR) vaccine increases the risk of autism. The researchers observed no higher autism rates following MMR vaccination, including among children considered at higher risk for autism. In a subgroup analysis, vaccinated girls showed a 16%–21% lower risk of autism. The study also found no association between other routine childhood vaccines—such as DTaP and Hib—and an increased risk of autism spectrum disorder (ASD).
Source: American College of Physicians
A nationwide Danish cohort study of children born from 1999 through 2010 reports that the MMR vaccine does not increase autism risk, does not appear to trigger autism in susceptible children, and is not followed by clustering of autism diagnoses. The results are published in Annals of Internal Medicine.
Concerns about a possible link between the MMR vaccine and autism have persisted for years and continue to affect vaccination acceptance. These concerns are especially relevant now, as measles outbreaks have risen in parts of Europe and the United States, and health authorities have identified vaccine hesitancy as a major public-health challenge.
Researchers at Statens Serum Institut in Copenhagen used Danish national registries to examine whether MMR vaccination was associated with autism diagnoses overall, in various subgroups, or during specific time windows after immunization. The cohort included 657,461 children born to Danish-born mothers between 1999 and 2010, followed from age one through August 31, 2013. During more than five million person-years of follow-up, 6,517 children received an autism diagnosis.
Using survival analysis and Cox proportional hazards models, the investigators compared autism rates in MMR-vaccinated and MMR-unvaccinated children while adjusting for age, birth year, sex, other childhood vaccinations, sibling history of autism, and a composite autism risk score based on medical and family factors. The fully adjusted hazard ratio comparing vaccinated to unvaccinated children was 0.93 (95% confidence interval, 0.85 to 1.02), indicating no evidence of increased risk after MMR vaccination.
The absence of an elevated autism risk after MMR vaccination held across multiple subgroup analyses. The researchers found no increased risk among children with a sibling history of autism, among those with higher calculated autism risk scores, or when examining different time intervals after administration of the vaccine. The study also evaluated other routine childhood vaccines, including diphtheria-tetanus-acellular pertussis (DTaP) and Haemophilus influenzae type b (Hib), and found no link between these vaccinations and higher autism risk—even in groups with genetic or familial risk factors.
Notably, a subgroup analysis showed that girls who received the MMR vaccine had a reduced risk of autism, with estimates ranging from a 16% to 21% reduction. While this finding emerged in stratified analyses, the overall conclusion remained that vaccination was not associated with increased autism incidence.
The investigators emphasize that this study strengthens the existing evidence base because of its large size, long follow-up, and the ability to examine potential susceptible subgroups and temporal clustering of diagnoses. One limitation acknowledged by the authors is that individual medical charts were not reviewed; the study relied on registry-recorded diagnoses and vaccination data.
Source:
American College of Physicians
Media Contacts:
Lauren Evans – American College of Physicians
Image Source:
The image is in the public domain.
Original Research: Open access
“Measles, Mumps, Rubella Vaccination and Autism: A Nationwide Cohort Study.” Anders Hviid, DrMedSci; Jørgen Vinsløv Hansen, PhD; Morten Frisch, DrMedSci; Mads Melbye, DrMedSci. Annals of Internal Medicine April 16, 2019. DOI: 10.7326/M18-2101
Abstract
Measles, Mumps, Rubella Vaccination and Autism: A Nationwide Cohort Study
Background:
Concerns linking the measles, mumps, and rubella (MMR) vaccine with autism persist and can undermine vaccination programs.
Objective:
To determine whether MMR vaccination is associated with an increased risk of autism in children overall, in defined subgroups, or in specific post-vaccination time periods.
Design and Setting:
Nationwide cohort study using Danish population registries.
Participants:
657,461 children born in Denmark from 1999 through 31 December 2010, followed from age one through 31 August 2013.
Measurements:
Registry data linked vaccination records, autism diagnoses, information on other childhood vaccines, sibling history of autism, and measures of autism risk. Time-to-diagnosis analyses used Cox proportional hazards regression adjusted for relevant covariates.
Results:
Across 5,025,754 person-years, 6,517 children were diagnosed with autism (incidence rate, 129.7 per 100,000 person-years). The fully adjusted hazard ratio for autism comparing MMR-vaccinated with MMR-unvaccinated children was 0.93 (95% CI, 0.85 to 1.02). No increased risk was found in subgroup or time-window analyses.
Limitation:
The study did not include review of individual medical charts.
Conclusion:
The results strongly support that MMR vaccination does not increase autism risk, does not trigger autism in children considered susceptible, and is not associated with clustering of autism diagnoses following vaccination. The large sample and subgroup analyses add statistical power and address questions about susceptible groups and clustering of cases.
Primary Funding Source:
Novo Nordisk Foundation and Danish Ministry of Health.