Epidemiological and Clinical Features of Clade Ib Mpox Virus Infection in African Countries and Non-Endemic Contexts: A Narrative Review

Mpox virus (MPXV) Clade I has historically been confined to sporadic zoonotic outbreaks in Central Africa. In 2023, a novel Clade I lineage (designated Clade Ib) emerged, exhibiting sustained human-to-human transmission. Emerging evidence suggests that the epidemiological and clinical profile of Clade Ib differs between endemic African settings and non-endemic contexts, with implications for surveillance, diagnosis, and clinical management. This narrative review synthesizes current evidence on this divergence, drawing on 54 eligible studies identified through targeted PubMed searches supplemented by institutional surveillance sources covering September 2023 to 16 August 2026. Age and sex distribution and route of transmission vary widely and dynamically across African outbreaks, whereas non-African cases remain almost uniformly adult and linked to sexual networks among men who have sex with men (MSM), with anogenital disease and proctitis increasingly reported over time. Case burden remains higher in Africa, and case-fatality estimates are markedly lower than those of Clade Ia. However, several differences, including those in hospitalization and mortality, are confounded by different case identification methods between hospital-based African cohorts and population-based non-African surveillance, and data on pregnancy, pediatric disease, and infection in immunocompromised patients remain almost entirely absent outside Africa.