Measles vaccination coverage remains below herd immunity after postelimination outbreak

A repeated cross-sectional study found that measles–mumps–rubella (MMR) vaccination coverage remained below herd immunity thresholds up to 20 months after a postelimination outbreak in central Ohio, with only modest improvements observed across a large primary care network (PCN). This research was presented at the Pediatric Academic Societies (PAS) 2026 Meeting.^1,2

Measles remains one of the most contagious vaccine-preventable diseases, requiring at least 93% population immunity to prevent sustained transmission. During 2022–2023, a large outbreak in central Ohio primarily affected unvaccinated children, prompting public health interventions including outbreak notifications, quarantines, and expanded access to vaccination. Despite these efforts, local estimates of vaccination coverage have been limited, particularly among subgroups disproportionately affected by prior outbreaks.

Study design evaluates vaccination coverage over 20 months

Investigators conducted electronic medical record–based surveillance of 133,476 children younger than 15 years within a central Ohio PCN. The study evaluated vaccination coverage at outbreak onset in October 2022 and at 12- and 20-month follow-up intervals. Outcomes included timely receipt of the first MMR dose (MMR1), timely receipt of the second dose (MMR2), and receipt of at least one valid dose. Analyses also examined differences between children of Somali descent and their peers.

MMR coverage shows minimal improvement after outbreak

At outbreak onset, timely MMR1 coverage was 53.6%, substantially below the threshold required for herd immunity. This rate remained unchanged at both 12 and 20 months, with an absolute risk difference of 0.1 percentage points (95% CI, –0.3 to 0.4; P = .76). Timely MMR2 coverage increased modestly from 57.9% to 60.2% over 20 months (absolute risk difference, 2.3 percentage points; 95% CI, 1.7–2.8; P < .001). Similarly, receipt of at least 1 MMR dose by 84 months increased slightly from 77.3% to 77.9% (absolute risk difference, 0.6 percentage points; 95% CI, 0.2–1.0; P = .003).

Disparities persist among children of Somali descent

Disparities in vaccination coverage were observed. Children of Somali descent had approximately 20 percentage points lower timely MMR1 coverage compared with non-Somali peers at all time points (P < .001). However, differences between groups in MMR2 and overall dose coverage were small and not statistically significant by 20 months.

Public health response requires sustained, targeted strategies

The findings indicate that, despite targeted public health interventions, vaccination coverage remained insufficient to prevent future outbreaks. According to the study authors, these results underscore the need for sustained efforts to improve immunization rates, particularly in communities with lower uptake.

“Our findings show that measles outbreaks reveal, but do not resolve, underlying gaps in population immunity,” said Rosemary A. 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.”

The study highlights the importance of continued surveillance and targeted interventions to address gaps in vaccine coverage. Although modest gains were observed in second-dose and overall vaccination rates, the lack of improvement in timely first-dose coverage suggests ongoing barriers to early immunization.

For pediatricians, these findings emphasize the need to support routine vaccination, reinforce timely immunization schedules, and engage with communities experiencing lower uptake. Persistent immunity gaps following an outbreak may leave populations vulnerable to future transmission, even in settings where measles had previously been eliminated.

References

1. Pediatric Academic Societies. New Study Examines Measles Vaccination Coverage After a Postelimination Outbreak. Pediatric Academic Societies. Press release. April 24, 2026. Accessed April 24, 2026.

2. Martoma RA, Martoma J, Majumder M. Surveillance of Measles Vaccination Coverage After a Postelimination Outbreak: A Repeated Cross-Sectional Study in a Primary Care Network. Abstract. Presented at: Pediatric Academic Societies 2026 Meeting. Boston, MA. April 24-27, 2026.