Effect of armed conflict on measles surveillance and zero-dose vaccination status in Tigray, Ethiopia, 2018–2024

Abstract Background Armed conflict disrupts health systems, undermining routine immunization and disease surveillance. These disruptions can delay outbreak detection and allow population susceptibility to accumulate unnoticed. This study assessed the impact of the 2020–2022 conflict in Tigray, Ethiopia, on measles epidemiology, focusing on surveillance reporting, age distribution of cases, and vaccination status. Methods We conducted a retrospective longitudinal analysis of national case-based measles surveillance data from Ethiopia (2018–2024; n = 69,866). Changes in measles surveillance, age distribution, and zero-dose vaccination status across the pre-conflict (2018–2019), conflict peak (2020–2022), and post-conflict recovery (2023–2024) periods were examined. Two-way analysis of variance examined regional differences in age at infection across phases. Multivariable logistic regression estimated adjusted odds ratios (aORs) for confirmed measles cases being unvaccinated (zero-dose), using the pre-conflict period as the reference and adjusting for age and sex. Surveillance quality was assessed using demographic data completeness. Results During the conflict peak, reported measles cases from Tigray declined to 0.01% of nationally reported cases, consistent with near-total surveillance collapse. After hostilities ended, a marked pediatric shift emerged, with the median age of infection in Tigray declining from 24.0 years during the conflict to 5.0 years in the post-conflict period ( p < 0.0001), a pattern not observed in other regions. Compared with the pre-conflict baseline, the odds that a confirmed measles case was zero-dose were substantially higher during the conflict peak (aOR: 71.43; 95% CI: 14.1–1000.0) and remained elevated during post-conflict recovery (aOR: 2.49; 95% CI: 1.17–5.52). During the conflict peak, 50% of confirmed cases in Tigray lacked sex-disaggregated data. Conclusion The conflict was associated with a near-complete collapse of measles surveillance, marked changes in the age distribution of reported cases, and an increased proportion of zero-dose measles cases. These findings highlight the need for resilient surveillance systems and targeted catch-up vaccination during post-conflict recovery.