Measles outbreak propagated by poor isolation practices in schools and health facilities, Mityana District, Uganda, March–September 2025

In April 2025, Mityana District in Central Uganda confirmed a measles outbreak involving one suspected death. We investigated to determine outbreak magnitude, identify transmission risk factors, and assess vaccination coverage (VC) and vaccine effectiveness (VE) to inform control and prevention measures. We defined a suspected case as onset of fever and maculopapular rash with cough, coryza, or conjunctivitis in a Mityana District resident during March–September 2025; a confirmed case was a suspected case with measles IgM positivity. We identified cases through health facility record review and active community case search. We conducted descriptive epidemiology and an age-matched case-control study (1:1) using neighborhood controls. We used conditional logistic regression to estimate odds ratios (ORs) and 95% CIs for factors associated with infection. We estimated VC as the proportion of vaccinated controls and calculated VE as 1-OR MH × 100%. We identified 100 case-patients (5 confirmed, 95 suspected), including one death. The earliest case was a 12-month-old male from Kiboga District, where a measles outbreak was ongoing. The highest attack rates occurred among children aged 9–17 months (11/10,000) and 18–59 months (10/10,000). Receipt of measles-rubella (MR) vaccine dose 1 (MR1) was protective (aOR = 0.24; 95% CI: 0.095–0.53). School attendance (aOR = 3.9; 95% CI: 1.2–12) and a health facility visit within three weeks before illness onset (aOR = 2.6; 95% CI: 1.2–5.7) were associated with increased risk. VE was 67% (95% CI: 31%-85%) for MR1 and 81% (95% CI: 24%-99%) for MR2. VC among controls was 70% for MR1 and 52% for MR2. The outbreak was likely introduced from a neighboring district and sustained by suboptimal MR vaccination coverage and transmission in schools and health facilities. We recommended immediate targeted mass MR vaccination campaigns and strengthened triage and isolation in schools and health facilities to interrupt transmission. To prevent future outbreaks, we recommended strengthening routine immunization, particularly MR2, and enhancing community sensitization and surveillance for early detection and response.