Abstract
Diphtheria has returned to the WHO African Region as a large, sustained outbreak, yet national immunization indicators for the affected countries look, in aggregate, unremarkable. This narrative review asks why rising case counts coexist with seemingly adequate coverage. We reviewed peer-reviewed outbreak analyses (2022–2026) from Nigeria, Yemen, Guinea, Haiti and South Africa, peer-reviewed studies of zero-dose and under-immunized children, and official WHO African Region communications. Three observations emerge. First, the 2025 resurgence is demographically concentrated: across the Region more than 90% of reported cases occurred in unvaccinated or under-immunized children, and country studies consistently attribute the majority of cases and deaths to zero-dose and late-presenting children. Second, this concentration is invisible to the coverage indicators that surveillance tracks, because district-level DTP3 averages smooth over the pockets—fishing islands, pastoralist zones, peri-urban settlements and conflict areas—where zero-dose prevalence reaches 69–92%. Third, the same children excluded from vaccination are also the least likely to reach diphtheria-antitoxin-capable care, so immunization exclusion and treatment failure are one problem seen from two sides. We argue that outbreak response should pair fine-grained immunization intelligence (who and where remains un- or under-immunized) with district-level treatment-readiness tracking, and report the two together rather than separately.