A new study of over 2.5 million children published in The Pediatric Infectious Disease Journal indicates that getting the measles, mumps, and rubella vaccine before the age of two does not correlate with a higher risk of childhood autism. Researchers examined electronic health records and determined that the precise timing of the immunization was not linked to a child’s likelihood of being diagnosed with the condition.
Data from 2.5 Million Children Analyzed in EHR Study
The research, led by Todd L. Burstain of UW Medicine alongside Dale Jacques and Jennifer M. Burstain, utilized records from the Cosmos electronic health record database. This extensive collection of data included 2,560,035 children from clinics and hospitals throughout the United States who had at least one routine primary care visit between 12 and 24 months of age. The prevalence of childhood autism in this specific sample stood at 2.55 percent. The study focused strictly on a narrow diagnostic code for childhood autism rather than the broader autism spectrum disorder, which affects an estimated 3.2 percent of children in the United States.
To establish a clear timeline, investigators excluded any children diagnosed with autism at or before 11 months of age. By the time they reached 24 months of age, 91.4 percent of the children in the sample had been given their first dose of the measles, mumps, and rubella vaccine. The children were followed up to age eight or until December 2024. For the primary analysis regarding vaccination between 11.5 and 24 months, the 99 percent confidence interval was 0.91 to 1.03, with an adjusted hazard ratio of 0.97. Because this range includes 1.0, the statistical result indicates no difference in risk between vaccinated and unvaccinated groups.
Addressing Observational Study Bias With Age-Anchored Landmark Analysis
Observational studies on vaccine safety often face design challenges because factors like family healthcare habits, early parental concerns, and child age influence both vaccination timing and autism diagnoses. To tackle these complexities, the authors employed an age-anchored landmark analysis. This method grouped children by the age window in which vaccination decisions typically occur, comparing vaccinated and unvaccinated children within those defined windows to reduce bias.
The investigators categorized the children into specific age intervals, such as 11.5 to 12.5 months, 12.5 to 13.5 months, and up to 24 months. Within each window, they compared children who received their first dose against those who had not yet been vaccinated. To ensure a fair comparison, analysts adjusted for maternal age, race and ethnicity, gestational age at birth, whether the baby was small for its gestational age or multiple births, diabetes or genital or urinary tract infections during pregnancy, neighborhood disadvantage, and geographic region. In two later windows, spanning 14.5 to 17.5 months and 17.5 to 24 months, vaccinated children showed slightly lower rates of autism diagnosis, with hazard ratios of 0.90 and 0.92. The authors attributed these minor deviations to leftover data bias rather than any protective vaccine effect.
Negative Control Testing and Historical Context of Vaccine Fears
To verify their methodology, the researchers tested a negative control exposure by examining the pneumococcal conjugate vaccine booster. Given around 12 to 15 months to prevent bacterial infections, this booster has no theoretical link to autism. The similar results observed for the pneumococcal booster suggest the analysis did not generate false signals tied to routine checkups. These findings echo a large body of prior research refuting anxieties that largely stem from a retracted 1998 case series involving just 12 children.
Despite the large dataset, the study carried limitations. The medical records lacked information on family history of autism, a factor that could potentially skew data if parents of a diagnosed child delay vaccination for younger siblings. Vaccinated children had a median follow-up of 853 days compared to 366 days for unvaccinated children. Longer healthcare interaction typically provides more opportunities for a formal diagnosis, yet researchers still uncovered no link between the immunization and autism.
Common Questions About the MMR Vaccine and Autism Research
What database was used for this MMR vaccine study?
Researchers analyzed electronic health records from Cosmos, a massive database covering hospitals and clinics across the United States. The dataset included records for 2,560,035 children.
What statistical method did researchers use to control for bias?
The team used an age-anchored landmark analysis, grouping children into specific age windows—such as 11.5 to 12.5 months—to compare vaccinated and unvaccinated children within the same developmental periods.
Did the study look at the entire autism spectrum?
No, the analysis focused specifically on a narrower diagnostic code for childhood autism rather than the full autism spectrum disorder, which accounts for why the sample’s prevalence was 2.55 percent.
What was the purpose of testing the pneumococcal conjugate vaccine?
The researchers used the pneumococcal booster as a negative control exposure because it has no theoretical link to autism, verifying that their methodology did not produce spurious links to routine checkup visits.
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