Barriers & coverage outcomes of inactivated polio vaccine & oral polio vaccine in humanitarian settings: a scoping review

Abstract

Polio is targeted for global eradication by 2029. Immunization campaigns face significant challenges in humanitarian emergencies due to instability, population displacement, and health infrastructure collapse. The two primary vaccines used, Inactivated Polio Vaccine (IPV) and Oral Polio Vaccine (OPV), have distinct delivery requirements. This scoping review maps key implementation barriers for each delivery mechanism in disaster settings and assesses reported coverage outcomes to inform vaccine selection in emergencies. Following the PRISMA extension for Scoping Reviews (PRISMA-ScR), we searched PubMed, EMBASE, Web of Science, and Cochrane Library (CENTRAL), supplemented by a targeted grey-literature search. Studies were included if they focused on OPV and/or IPV campaigns in humanitarian crises, provided data on coverage or logistics, and were published in English within the last 20 years. Included studies were appraised using JBI Critical Appraisal Tools. The search identified 1604 studies, of which 24 met inclusion criteria. Key IPV implementation barriers were higher operational costs, the requirement for skilled health workers, reliance on fixed-post delivery, and complex cold chain requirements. Prominent OPV barriers included bans on campaigns by armed groups, misinformation leading to vaccine refusal, and restricted access to populations due to insecurity. Three studies reported high IPV coverage (80%-102.9%) when delivered alongside OPV with strong community engagement. Fourteen studies reported OPV campaigns frequently exceeding 90% coverage, particularly where supported by effective partnerships and social mobilization. Within the evidence mapped by this review, OPV emerges as the more practical mainstay for large-scale campaigns in crisis settings, owing to its lower cost, ease of administration, and repeatedly high reported coverage. This finding should be read alongside three caveats. The evidence base is asymmetric (three IPV effectiveness studies versus fourteen for OPV), the outcome measured was administrative coverage rather than seroconversion or interruption of transmission, and several OPV campaigns reporting high coverage were themselves responses to circulating vaccine-derived poliovirus. IPV faces logistical, operational, and cost barriers limiting its scalability in emergencies but remains essential to the eradication endgame. Regardless of delivery method, effective partnerships and community engagement are critical to campaign success. Further research on IPV-only campaign implementation in humanitarian contexts is needed. This review was not registered. This is the first scoping review to identify implementation barriers and compare coverage outcomes of OPV and IPV Vaccines in humanitarian emergencies. We examine logistical, financial, and sociopolitical barriers for each mechanism of delivery, highlighting their distinct implementation challenges in crisis settings. Given the GPEI’s eradication goal by 2029, our review provides policymakers and operational actors with an evidence base to inform decisions on future implementation strategies in disaster areas. We found a limited number of publications on IPV-only immunization campaigns in crisis settings, indicating a knowledge gap to guide future implementation research.