Timely receipt of routine 2- and 4-month vaccinations emerged as the strongest predictor of measles, mumps, and rubella immunization by age 2 years, according to a cohort study of 321,743 pediatric patients with regular health care access published in JAMA Network Open.
Pediatric patients who received their 2-month vaccines late demonstrated nearly 7 times the odds of receiving no measles, mumps, and rubella (MMR) vaccination by 24 months compared with those vaccinated on schedule, while late 4-month vaccination conferred more than 6 times the odds of MMR nonvaccination in the post–COVID-19 pandemic cohort.
The analysis revealed declining MMR coverage despite consistent health care engagement. Timely first-dose MMR vaccination decreased from 80% in 2021 (nearly 40,000 of approximately 50,000 patients) to 77% in 2024 (approximately 40,000 of 52,000 patients). Nonvaccination by age 2 years increased from 5% in 2020 (approximately 2,600 of nearly 50,000 patients) to 8% in 2024 (approximately 4,000 of 52,000 patients) .
"A total of 1,723 measles cases have been reported as of November 12, 2025, in the US, reaching their highest levels since elimination in 2000," wrote lead study author Nina B. Masters, PhD, MPH, of Truveta Research, and colleagues.
The cohort included approximately 166,000 boys (52%) and nearly 156,000 girls (48%) born between 2017 and 2023 who received care within Truveta Data, an electronic health record database encompassing more than 120 million patients. Inclusion required outpatient visits at 0 to 2 months, 3 to 11 months, 12 to 21 months, and 22 to 25 months of age, ensuring 2 full years of follow-up while excluding patients without regular health care system engagement.
Overall, approximately 252,000 pediatric patients (78%) received timely MMR vaccination, nearly 45,000 (14%) received late vaccination, and approximately 22,000 (7%) had no recorded MMR vaccination by 24 months. An additional approximately 3,100 pediatric patients (1%) received early vaccination between 6 and 11 months.
Mixed-effect logistic regression models with state-level random effects, stratified by pre– vs post–COVID-19 pandemic MMR eligibility (visits before March 2020 vs after September 2020), identified multiple factors associated with nonvaccination. Male sex conferred slightly higher odds of nonvaccination. White race demonstrated nearly 1.5 times the odds compared with Black race, while non-Hispanic or Latino ethnicity showed 1.5 times the odds relative to Hispanic ethnicity.
Rural residence was associated with slightly higher odds of nonvaccination, though this relationship reversed comparing late vs timely vaccination. Adherence to the American Academy of Pediatrics well-child visit schedule demonstrated substantially lower odds of nonvaccination.
The temporal analysis revealed an increasing risk of nonvaccination in recent cohorts. Pediatric patients eligible for MMR vaccination in 2024 had 1.35 times the odds of nonvaccination compared with those eligible in 2020, after adjusting for all other factors.
Coverage of early childhood vaccinations showed similar declining trends. Timely 2-month vaccination ranged from 85% for diphtheria, tetanus, and acellular pertussis to 84% for rotavirus, while timely 4-month vaccination ranged from 84% to 82%, respectively. Timely first diphtheria, tetanus, and acellular pertussis vaccination decreased from 87% in 2019 (approximately 44,000 of 51,000 patients) to 84% in 2023 (approximately 15,000 of nearly 18,000 patients) while timely second doses declined from 85% in 2020 (approximately 43,000 of nearly 51,000 patients) to 82% in 2023 (approximately 15,000 of nearly 18,000 patients).
The study population included approximately 195,000 White pediatric patients (61%), nearly 43,000 Hispanic or Latino pediatric patients (13%), approximately 33,000 Black or African American pediatric patients (10%), and nearly 20,000 Asian pediatric patients (6%). Approximately 250,000 pediatric patients (78%) resided in urban areas, and about 61,000 (19%) in rural areas. Missing race and ethnicity data affected approximately 48,000 (15%) and nearly 52,000 (16%) pediatric patients, respectively; these patients were retained in analyses as unknown categories.
Vaccine timing classifications were strict following Advisory Committee on Immunization Practices guidelines with a 4-day grace period before minimum administration age. Vaccinations received before the minimum age or violating minimum dosage intervals were excluded as potential data errors. Composite timeliness indicators for 2- and 4-month series classified pediatric patients as on time only if all vaccines in the series were administered within recommended windows.
Study limitations included geographic concentration, with data primarily from Texas, Washington, Wisconsin, Iowa, California, Illinois, Michigan, Louisiana, Oregon, and Hawaii. The requirement for 4 outpatient visits likely selected for higher care-seeking behavior and vaccination coverage than the general population. Vaccinations administered outside Truveta constituent facilities, during travel, or at pharmacies would not be captured, though assuming stable out-of-system vaccination rates over time would affect overall coverage but not trends.
"By including individuals with consistent medical care over their first 2 years of life, the results of this analysis likely highlight decreases in timely vaccination associated with increasing vaccine hesitancy more than access issues," the researchers wrote.
The cohort study followed Strengthening the Reporting of Observational Studies in Epidemiology reporting guidelines. Data underwent syntactic and semantic normalization before deidentification under HIPAA Privacy Rule expert determination. The analysis used deidentified data and therefore did not constitute human participant research requiring institutional review board review under federal regulations.
Disclosures can be found in the published study.
Source: JAMA Network Open
