Measles Vaccination Coverage After a Postelimination Outbreak.

Importance: Sustaining measles elimination in the US requires high population-level vaccination coverage. Postelimination outbreaks expose persistent immunity gaps, especially in underimmunized communities. Understanding vaccination trends after such outbreaks is critical for public health responses and preparedness. Objective: To evaluate changes in measles-mumps-rubella (MMR) vaccination coverage after a large postelimination measles outbreak in a major US pediatric primary care population. Design, Setting, and Participants: This repeated, surveillance cross-sectional study was conducted at an extensive central Ohio pediatric primary care network that served approximately 150 000 children at the following 3 time points: outbreak onset (October 8, 2022), 12 months (October 8, 2023), and 20 months (June 8, 2024). Children younger than 15 years with 1 well-child visit or more in the prior 24 months were analyzed. Children of Somali descent were analyzed as a prespecified subgroup. Exposure: Receipt of valid MMR vaccine doses per Centers for Disease Control and Prevention guidelines. Main Outcomes and Measures: Primary outcomes were (1) timely MMR vaccine 1 receipt by 16 months of age, (2) timely MMR vaccine 2 receipt 28 days or more after MMR vaccine 1 and by 84 months of age, and (3) receipt of 1 valid MMR dose or more by 84 months of age. Coverage was assessed at each time point. Risk differences were estimated using binomial generalized linear models with an identity link. The secondary outcome was MMR coverage stratified by Somali descent. Results: At 20 months after measles onset, the cohort included 149 092 children (median [IQR] age, 7.96 [4.23-11.50] years; 76 469 [51.3%] male; 12 880 [8.6%] Somali descent and 136 212 [91.4%] non-Somali descent). Timely MMR vaccine dose 1 coverage remained unchanged (66 143 of 123 490 [53.6%] at 0 months and 74 157 of 138 301 [53.6%] at 20 months; risk difference, 0.1 percentage points; 95% CI, -0.3 to 0.4 percentage points; P = .76). Timely MMR vaccine dose 2 coverage increased modestly (44 210 of 76 410 [57.9%] at 0 months and 50 875 of 84 576 [60.2%] at 20 months; risk difference, 2.3 percentage points; 95% CI, 1.7-2.8 percentage points; P < .001). Receipt of at least 1 MMR dose by 84 months of age increased from 59 049 of 76 410 (77.3%) at 0 months to 65 891 of 84 576 (77.9%) at 20 months (risk difference, 0.6 percentage points; 95% CI, 0.2-1.0 percentage points; P = .003). Children of Somali descent had significantly lower timely MMR vaccine dose 1 coverage at all time points (overall risk difference at baseline, -19.7 percentage points; 95% CI, -20.7 to -18.8 percentage points; P < .001). Conclusions and Relevance: In this repeated cross-sectional study of 149 092 children in a large central Ohio primary care network during the 20 months after outbreak onset, all measures of MMR coverage remained well below the 93% herd immunity threshold. These persistent, population-wide immunity gaps suggest the need for sustained, equity-focused public health strategies to maintain measles elimination.