Predictors of Delayed or Absent Measles, Mumps, and Rubella Vaccination in the US, 2018-2025

Importance1,168 measles cases have been reported as of June 6, 2025, and cases for the year are likely to soon exceed the highest levels seen since elimination in 2000. MMR (measles, mumps, rubella) vaccination rates have declined, and predictors of delayed and missed vaccination since the COVID-19 pandemic are not well explored. ObjectiveCharacterize rates and trends of timely MMR vaccination among children and assess predictors of late and non-vaccination by two years of age. DesignIn this retrospective cohort study, infants who accessed routine care within the first two months, first year, and second year of life were followed for 24 months to assess vaccination outcomes between January 1, 2018, and April 30, 2025. SettingChildren seeking care within a healthcare system partnering with Truveta, an electronic health record database from a collective of US health care systems. ParticipantsThis study included 321,743 children under the age of two years. ExposuresThe primary exposure(s) were timely receipt of routine 2- and 4-month immunizations and adherence to the AAP well child visit schedule. Main Outcome(s) and Measure(s)The primary outcome was timely, late, or no receipt of MMR by two years of age. Associations with primary exposures and sociodemographic factors were modeled using mixed effect logistic regression with state-level random effects. Models were stratified by pre-versus post-COVID-19 MMR eligibility, with results after the COVID-19 pandemic reported as primary. ResultsIn this study of 321,743 children, 78.4% received their first MMR on time, rising from 75.6% (12,840/16,978) in 2018, to 79.9% (39,739/49,767) in 2021, then declining to 76.9% (40,306/52,388) in 2024. The strongest predictor of no MMR vaccination by two years was late administration of a childs second-month vaccines (aOR 6.96 [6.60-7.34]) and fourth-month vaccines (aOR 6.16 [5.84,6.50]). Conclusions and RelevanceIn this cohort study, most children received their MMR vaccine on time, but the proportion of children not receiving MMR by two years of age has steadily grown each year since the COVID-19 pandemic. Children who did not receive their 2- and 4-month vaccines on time were significantly more likely to not receive any MMR by two years, highlighting early opportunities for intervention.