Operational drivers of measles outbreaks in Uganda: a multi-district outbreak causality analysis, July 2025- March 2026

Background: Measles outbreaks in Uganda persist despite the availability of an effective vaccine, suggesting persistent immunity gaps and health system weaknesses. We conducted a multi-district outbreak causality analysis (OCA) to identify programmatic and health-system contributors to measles outbreaks and inform measles elimination programming. Methods: We conducted a cross-sectional mixed-methods OCA across 12 affected districts in Uganda (2025-2026), guided by the World Health Organization framework. We reviewed measles case investigation reports and triangulated findings with qualitative interviews with district health teams, health workers, surveillance and immunisation staff, community leaders, Village Health Teams, and caregivers. We deductively analysed data to identify causal pathways and contributing factors. Findings were organized into four prespecified analytical themes: immunization service delivery, caregiver access and demand, surveillance and case detection, and outbreak preparedness and response. Results: The 12 districts reported 1,302 cases, including 80 laboratory-confirmed cases and 10 suspected deaths (case-fatality rate: 0.77%); 46.5% (n=606) occurred among children aged 18-59 months. Most cases (65.3%) occurred in unvaccinated children, versus 1.0% in children with both measles-rubella (MR) doses. Across districts, incomplete MR2 implementation, irregular outreach, inconsistent fixed-site vaccination, weak follow-up of children who missed vaccination, and transport and distance barriers contributed to persistent immunity gaps. Low clinical suspicion, limited engagement of Village Health Teams, laboratory and surveillance-information bottlenecks, absence of pre-positioned response plans, delayed response activation, and inadequate isolation capacity further limited early detection and control. Conclusion: Measles outbreaks were driven primarily by missed vaccination, especially incomplete delivery of the two-dose MR schedule, compounded by access barriers, delayed case detection, and limited outbreak preparedness. Strengthening routine MR1 and MR2 delivery, targeted catch-up vaccination, community-linked surveillance, and pre-positioned district response plans with clear activation triggers will be critical to closing immunity gaps and accelerating measles elimination in Uganda.