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The PAS Meeting connects thousands of leading pediatric researchers, clinicians, and educators worldwide, united by a shared mission: connecting the global academic pediatric community to advance scientific discovery and promote innovation in child and adolescent health.
Credit: Pediatric Academic Societies
BOSTON, April 24, 2026 – A new study examined measles vaccination coverage following a large postelimination outbreak, primarily affecting unvaccinated children. Findings from the study will be presented during the Pediatric Academic Societies (PAS) 2026 Meeting, taking place April 24-27 in Boston.
Measles, one of the most contagious vaccine-preventable diseases, requires ≥93% population immunity to prevent sustained transmission. In 2022–2023, a large postelimination outbreak occurred in central Ohio. Public health interventions—including outbreak notifications, quarantines, and expanded vaccination access—were implemented. However, robust local estimates of measles–mumps–rubella (MMR) vaccination coverage are limited. Prior outbreak reports identified children of Somali-descent as disproportionately affected, underscoring the need to assess subgroup disparities to sustain elimination, strengthen immunization systems, and inform surveillance.
The study found that 20 months after the outbreak, MMR coverage across the entire primary care network (PCN) population remained well below herd immunity levels, with minimal gains. These findings highlight the fragility of measles elimination, showing that even after a postelimination outbreak, system-wide immunity deficits persist and require sustained, equity-focused strategies.
“Our findings show that measles outbreaks reveal, but do not resolve, underlying gaps in population immunity,” said Rosemary Martoma, MD, fellow at Boston Children’s Hospital and Harvard Medical School and lead author of the study. “Addressing these gaps requires coordinated public health efforts, including vaccination, timely awareness in healthcare settings, early identification of cases, and community-centered outreach.”
This work was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) of the National Institutes of Health (NIH) under award number T32HD040128.
Additional information is included in the below research abstract. The PAS Meeting connects thousands of leading pediatric researchers, clinicians and educators worldwide. View the full schedule in the PAS 2026 program guide. For more information about the PAS Meeting, please visit www.pas-meeting.org.
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About the Pediatric Academic Societies (PAS) Meeting
The Pediatric Academic Societies (PAS) Meeting connects thousands of leading pediatric researchers, clinicians, and educators worldwide, united by a shared mission: connecting the global academic pediatric community to advance scientific discovery and promote innovation in child and adolescent health. PAS is a partnership of four premier pediatric associations: the American Academy of Pediatrics (AAP), the Academic Pediatric Association (APA), the American Pediatric Society (APS), and the Society for Pediatric Research (SPR). For more information, visit www.pas-meeting.org. Follow us on X, Facebook, and Instagram.
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Abstract: Surveillance of Measles Vaccination Coverage After a Postelimination Outbreak: A Repeated Cross-Sectional Study in a Primary Care Network
Presenting Author
Rosemary A. Martoma, MD, MBChB, fellow in General Academic Pediatrics and the Computational Health Informatics Program at Boston Children’s Hospital and Harvard Medical School
Organization
Boston Children’s Hospital
Topic
Public Health & Prevention
Background
Measles, one of the most contagious vaccine-preventable diseases, requires ≥93% population immunity to prevent sustained transmission. In 2022–2023, a large postelimination outbreak occurred in central Ohio, primarily affecting unvaccinated children. Public health interventions—including outbreak notifications, quarantines, and expanded vaccination access—were implemented. However, robust local estimates of measles–mumps–rubella (MMR) vaccination coverage are limited. Prior outbreak reports identified children of Somali-descent as disproportionately affected, underscoring the need to assess subgroup disparities to sustain elimination, strengthen immunization systems, and inform surveillance.
Objective
To quantify changes in timely first-dose (MMR1), timely second-dose (MMR2), and any-dose (≥ 1 valid dose) MMR vaccination coverage in an extensive primary care network (PCN) over 20 months following a postelimination measles outbreak, and to assess differences in coverage trends between children of Somali descent and their peers.
Design/Methods
Electronic medical record (EMR)-based repeated cross-sectional surveillance of children < 15 years in a central Ohio PCN at outbreak onset (Oct 2022), 12 months, and 20 months. Inclusion: ≥1 well-child visit in the prior 24 months. Vaccination status from EMR using CDC definitions. Timely MMR1: receipt at 12–< 16 months; timely MMR2: ≥28 days after MMR1 and < 84 months. Given prior epidemiologic findings, Somali descent (identified from language/ethnicity fields) was included. Outcomes were analyzed with binomial generalized linear models; results reported as absolute risk differences (RD) with 95% CIs. P< 0.05 was significant.
Results
At outbreak onset (t=0; n=133,476), timely MMR1 coverage was 53.6%—well below herd immunity—and did not change at 12 or 20 months (RD=0.1 pp; 95% CI, –0.3–0.4; p=.76). Timely MMR2 rose modestly from 57.9% to 60.2% at 20 months (RD=2.3 pp; 95% CI, 1.7–2.8; p<.001). Any-dose coverage by 84 months increased slightly from 77.3% to 77.9% (RD=0.6 pp; 95% CI, 0.2–1.0; p=.003) (Figure 1). Somali children had ~20 pp lower timely MMR1 than peers at all time points (p<.001), whereas Somali–non-Somali differences for MMR2 and any-dose coverage were small and not significant by 20 months (Figure 2).
Conclusion(s)
20 months after the outbreak, MMR coverage across the entire PCN population remained well below herd immunity levels, with minimal gains. These findings highlight the fragility of measles elimination, showing that even after a postelimination outbreak, system-wide immunity deficits persist and require sustained, equity-focused strategies.
Co-Authors
Joshua Martoma, Undergraduate Researcher, University of California Berkeley
Maimuna Majumder, PhD, Assistant Professor, Harvard Medical School
Acknowledgement
This work was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) of the National Institutes of Health (NIH) under award number T32HD040128.
Tables and Images
MMR coverage in PCN children <15 years, population-wide: 0–20 months after a postelimination measles outbreak
Timely MMR1, timely MMR2, and any-dose MMR coverage among children younger than 15 years of age in a large Primary Care Network (PCN) at outbreak onset (t = 0), 12 months (t = 12), and 20 months (t = 20) following the 2022–2023 central Ohio postelimination measles outbreak. The red dashed line marks the herd immunity threshold (93%). Across all timepoints, coverage remained well below this threshold, indicating a persistent system-wide deficit in measles immunity. At outbreak onset (n = 133,476), timely MMR1 coverage was 53.6% and did not change at 12 or 20 months (RD = 0.1 percentage points; 95% CI, –0.3 to 0.4; p = .76). Timely MMR2 rose modestly from 57.9% to 60.2% by 20 months (RD = 2.3 pp; 95% CI, 1.7–2.8; p < .001). Any-dose MMR coverage increased only slightly, from 77.3% to 77.9% (RD = 0.6 pp; 95% CI, 0.2–1.0; p = .003). These findings highlight the limited impact of outbreak response efforts and the ongoing vulnerability of the PCN population nearly two years later. Abbreviations: PCN, Primary Care Network; MMR, measles-mumps-rubella vaccine; RD, risk difference; CI, confidence interval; pp, percentage points.
MMR coverage in PCN children <15 years, by ethnicity: 0 and 20 months after a postelimination measles outbreak
Timely MMR1, timely MMR2, and any-dose MMR coverage among Somali (orange bars) and non-Somali (blue bars) children younger than 15 years of age within a large Primary Care Network (PCN) at outbreak onset (t = 0) and 20 months later (t = 20) following the 2022–2023 central Ohio postelimination measles outbreak. The red dashed line marks the herd immunity threshold (93%). Across the entire PCN, coverage in both groups remained far below this threshold, underscoring a persistent system-wide deficit in measles immunity. Within this broader gap, Somali children consistently had markedly lower timely MMR1 coverage: at outbreak onset, 35.7% versus 55.4% (RD –19.7 percentage points; 95% CI, –20.6 to –18.7; p < .001), and at 20 months, 33.5% versus 55.6% (RD –22.1; 95% CI, –23.0 to –21.2; p < .001). By contrast, differences in timely MMR2 coverage (RD –0.6 pp; 95% CI, –1.5 to 0.3; p = .18 at baseline; RD –0.5 pp; 95% CI, –1.4 to 0.5; p = .33 at 20 months) and in receipt of any MMR dose (RD –0.3 pp; 95% CI, –1.2 to 0.6; p = .49 at baseline; RD 0.4 pp; 95% CI, –0.5 to 1.3; p = .37 at 20 months) were small and not statistically significant. Abbreviations: PCN, Primary Care Network; MMR, measles-mumps-rubella vaccine; RD, risk difference; CI, confidence interval; pp, percentage points.