Community burden of diphtheria during the 2023-24 epidemic in Kano State, Nigeria: a population-based household survey

BackgroundNigeria has experienced its largest recorded diphtheria outbreak since late 2022, centred on Kano State, where facility-based surveillance documented over 18,000 confirmed cases. The true community burden remains unknown. We conducted a population-based household survey to estimate community attack rates, mortality, vaccination coverage, and determinants of infection and death. MethodsWe performed a retrospective household survey (September-October 2024) using spatially randomised cluster sampling (65 clusters, ~15 households each; recall period January 2023 to interview). Survey-weighted analyses, multivariable logistic regression, and sensitivity analyses were used. FindingsWe enrolled 7,998 individuals from 1,068 households. The community attack rate was 1{middle dot}1% (95% CI 0{middle dot}7-1{middle dot}4), 4{middle dot}2 times (2{middle dot}7-5{middle dot}3) higher than facility-based estimates. The case fatality ratio was 8{middle dot}8% (1{middle dot}9-15{middle dot}6) overall and 21{middle dot}3% among children under five; two thirds of deaths occurred at home. Delayed care-seeking of four or more days was associated with markedly higher mortality (risk ratio 32{middle dot}6, 95% CI 2{middle dot}4-450{middle dot}0). Vaccination was strongly protective against death (vaccine effectiveness 57%, 95% CI 34-72%; E-value 4{middle dot}07). Among campaign-eligible children, routine EPI coverage was 58{middle dot}1% and campaign coverage was 52{middle dot}4%; 41{middle dot}9% (95% CI 39{middle dot}0-44{middle dot}9) of eligible children had no evidence of vaccination from either source. InterpretationCommunity diphtheria burden substantially exceeded facility surveillance estimates, with most deaths occurring outside the health system. Delayed care-seeking and low vaccination coverage were the main drivers of mortality, highlighting the need for improved community surveillance, decentralised care, and better-targeted vaccination.