Bridging the Gap: Impact of Surveillance Latency on Measles Transmission Dynamics and Age-Specific Burden in Ethiopia, 2018 - 2024

Background Ethiopia remains a high-burden measles setting, yet the drivers of protracted transmission and regional susceptibility remain poorly understood. This study analyzes seven years of national surveillance data to characterize demographic shifts, disease severity, and the impact of system performance on outbreak dynamics. Methods A longitudinal analysis was conducted on confirmed measles cases (2018–2024). We calculated age-specific attack rates (AR), case fatality rates (CFR), and utilized time-varying reproduction numbers (Rt​) to assess transmission intensity. The relationship between surveillance latency (onset-to-confirmation) and outbreak duration was evaluated. Results A total of 69,866 confirmed cases were analyzed. National burden was highest in the 1–4-year cohort (AR: 195/100,000). A significant regional shift in susceptibility was observed: median age of infection was 2.8 years in pastoralist regions (Somali) versus 7.2 years in urban centers (Addis Ababa). The overall CFR was 0.8%, peaking at 1.12% in infants < 9 months. Transmission intensity remained high during peaks (Rt​: 1.8–2.4). Critically, a median surveillance delay of 18 days (IQR: 12–25) was identified. This delay exceeds the 12.5 - day measles serial interval, creating a silent window of ~ 1.5 generations of transmission that allowed Rt​ to remain above 1.0 for up to 16 consecutive weeks. Conclusion Measles persistence in Ethiopia is driven by a dual failure: regional immunity gaps in pediatric populations and a surveillance-to-response process that lags behind viral biology. Elimination efforts must prioritize reducing diagnostic latency to under 12 days to outpace viral spread and implement age-targeted vaccination strategies tailored to regional demographic profiles.