Opportunities, Challenges and Proposed Solutions in Responding to Vaccine Preventable Disease Outbreaks in Humanitarian Settings

Humanitarian crises increasingly disrupt immunization systems, accelerating transmission of vaccine-preventable diseases (VPDs). Despite a robust global response architecture, reactive vaccination campaigns in humanitarian settings remain poorly documented, frequently delayed, and operationally constrained. We conducted a structured search of published and grey literature to identify and describe reactive vaccination campaigns for five VPDs, including measles, poliomyelitis, diphtheria, meningococcal meningitis, and yellow fever, across humanitarian settings between 2015 and 2024, drawing on 316 published and grey literature sources including WHO Disease Outbreak News, GOARN, and ReliefWeb. Given substantial gaps in publicly available reporting, findings are presented as a perspective to document implementation gaps and draw practical lessons rather than as a systematic review. Of 132 identified outbreaks, reactive vaccination campaigns were documented in 83 (63%). Where reported, the median response lag was 96 days (range: 14–533). Coverage data were available for 26 outbreaks (20%), ranging from 3.7% to 109%. Implementation barriers include political and security constraints, governance and coordination failures, community hesitancy and mistrust, and operational and technical breakdowns. Documented innovations included real-time digital monitoring, diplomatically negotiated access, community-led delivery, and adaptive multi-agency coordination. Despite existing global vaccination mechanisms, critical gaps in documentation, timeliness, and coverage persist. Closing these gaps requires standardized minimum reporting, pre-established coordination frameworks with defined decision authority, embedded community engagement, and context-specific operational guidance tailored to distinct humanitarian contexts. Systematizing and funding field-proven solutions is essential to protect the most vulnerable populations and strengthen global health security.