Four Years of an Unrelenting Outbreak: Trends, Geographic Spread and the Immunization Gap in Nigeria’s Diphtheria Epidemic, 2022–2026

Nigeria’s diphtheria outbreak began in May 2022 and has not ended. We extracted cumulative indicators from ten national situation reports published between January 2023 and January 2026. Confirmed cases rose from 111 to 40,460 and deaths from 22 to 2151, and states with confirmed cases from 4 to 31. After slowing in 2024, the outbreak returned in a second wave in 2025. The cumulative case fatality ratio (CFR) fell from 19.8% to 5.3%, but among cases added between reports it rose from 3.9% in late 2023 to 5.7% from December 2023 onward. Kano’s share of cases fell from 75.3% to 61.0% as Borno, Bauchi, Yobe and Katsina grew; Borno rose 4.5-fold in ten months. Children aged 1–14 years made up 62.9–69.4% of cases, and no more than 26.5% of cases in any report were fully vaccinated. Recent vaccination-status counts cannot be reconciled with earlier ones, and under 3% of cases were laboratory-confirmed. Control will need coordinated catch-up vaccination across the north, including boosters for school-age children and access for displaced communities. It will also need antitoxin stocked where patients present and surveillance data that can be compared over time.