Vaccination Rates Remain Low after Measles Outbreak

A low rate of vaccination leading to a measles outbreak in 2022 in central Ohio did not increase significantly or sufficiently to attain "herd immunity," despite the experience of the outbreak and provision of several public health initiatives.

"These findings suggest that public health messaging and interventions implemented during the outbreak did not translate into sustained system-level improvements in vaccination uptake," observe Rosemary Martoma, MD, Division of Primary Care Pediatrics, Nationwide Children's Hospital, Columbus, OH, and colleagues.

The outbreak produced 90 confirmed cases between June 12 and December 24, 2022, from what was modeled as an international importation index case. Although the regional public health agency had estimated MMR vaccination coverage at 80 to 90% during the outbreak, Martoma and colleagues did not find data to support that estimate, and modeled the 2-dose MMR coverage of eligible children at outbreak onset as 53% (95% Credible Interval, 21-77%).The investigators contrast this to the 93% coverage that they characterize as the "critical threshold necessary to sustain measles elimination."

The public health initiatives during the outbreak included outbreak notifications, quarantines, daycare closures and walk-in vaccination clinics.To ascertain the vaccination uptake in communities affected by the outbreak and targeted by public health initiatives, the investigators accessed electronic medical records (EMR) of the Columbus-based pediatric primary care network.¹

The records included dated administration of first dose (MMR1) and second dose (MMR2); and the assessment included whether MMR was timely: MMR1 between 12 and 16 months in children 16 months or older, and MMR2 between 28 days and 84 months in children 84 months or older.The cohort included 133,476 children younger than 15 years of age on the onset of the outbreak, and increased to 143,720 at 12 months and to 149,092 at 20 months.

The investigators found timely receipt of MMR1 remained unchanged after the outbreak, with 53.6% at the outset and 53.8% at 12 months and 53.6T at 20 months. MMR2 coverage did increase slightly, from 57.9% at 0 months to 59.9% at 12 months, and 60.2% at 20 months.Coverage with at least MMR1 by 84 months of age was 77.3% at 0 months, 77.9% at 12 months and 77.9% at 20 months.

"Our findings support the role of EMR-based surveillance as a complement to existing public health tools and underline the need for national investment in real-time, integrated immunization monitoring," Martoma and colleagues recommend.

A secondary measure found lower coverage in a Somali population, which the investigators found to be disproportionately affected during the early phase of the outbreak.The 11,689 Somali children represented 9.5% of the cohort at the onset of the outbreak.Their coverage of MMR1 was 35.7% at 0 months.Although differences narrowed by MMR2 eligibility, the gap in coverage between this group and the general population widened at 12 months and further widened to -22.1% less coverage at 20 months.

"These disparities suggest missed opportunities for early vaccination, which structural, cultural, or informational barriers may influence," Martoma and colleagues point out."However, differences narrowed by MMR2 eligibility, likely due to age-based catch-up, pre-kindergarten visits, or school-entry requirements.

"This convergence emphasizes the potential equity-promoting impact of age-based public health policies and underscores the importance of earlier engagement to close primary series gaps," the investigators state.

Reference

1.Martoma RA, Martoma JC, Majumder MS.Measles vaccination coverage after a post=elimination outbreak. JAMA Network Open. 2025; 8(9):e2533732. doi:10.1001/jamanetworkopen.2025.33732.