Measles Epidemiology, Transmission, and Surveillance Characteristics in Ethiopia, 2018-2024

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.

A longitudinal analysis of confirmed measles cases from 2018 to 2024 was conducted. Age-specific attack rates (AR) and case fatality rates (CFR) were calculated, and time-varying reproduction numbers (Rt) were estimated to assess transmission intensity. The relationship between surveillance latency (onset-to-confirmation) and outbreak characteristics, including duration and size, was evaluated.

A total of 69,866 confirmed cases were analyzed, of which 12.5% were laboratory confirmed and 87.5% were epidemiologically linked. The highest burden was observed among children aged 1-4 years (AR: 195 per 100,000). Substantial regional variation was evident, with the median age of infection at 2.8 years in pastoralist regions (e.g., Somali) and 7.2 years in urban settings (e.g., Addis Ababa). The overall CFR was 0.8%, peaking at 1.12% among infants aged < 9 months. Transmission intensity remained elevated during epidemic peaks (Rt: 1.8-2.4). The median onset-to-confirmation delay was 18 days, exceeding the estimated measles serial interval. While longer outbreaks were associated with larger outbreak size, no significant association was observed between surveillance delay and outbreak duration.

Persistent measles transmission in Ethiopia appears to be driven primarily by regional immunity gaps among susceptible pediatric populations, while prolonged surveillance delays remain an important operational concern for timely outbreak detection and response. Elimination efforts should prioritize strengthening routine immunization, closing regional immunity gaps, and improving surveillance timeliness. These findings also provide practical insights for other low- and middle-income countries seeking to strengthen measles control programs and surveillance systems in heterogeneous transmission settings.