Global burden of diphtheria, 1990–2021: a 204-country analysis of socioeconomic inequality based on SDI and DTP3 vaccination differences before and after the COVID-19 pandemic (GBD 2021)

Over the past three decades, global efforts have significantly reduced the diphtheria burden, but systemic challenges remain in low-SDI regions. Vaccination remains pivotal; however, post-pandemic declines in coverage underscore latent epidemic risks. Low-SDI regions require integrated nutrition-vaccination strategies, conflict-adapted delivery, and robust cold chains, while high-SDI areas should enhance genomic surveillance, adult boosters, and equitable technology sharing. This study provides the first systematic quantification of spatiotemporal diphtheria burden patterns, offering critical evidence for the WHO 2030 Diphtheria Elimination Roadmap. Eliminating regional disparities necessitates strengthened healthcare systems and adult booster immunization strategies.