Vaccine demands to achieve outbreak control for MPXV Clade I with one-time mass campaign in sub-Saharan Africa: scenario-based modelling study
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Background
Declining cross-protection from historical smallpox vaccination campaigns and persistent zoonotic reservoirs leave many sub-Saharan countries susceptible to mpox outbreaks. With millions of vaccine doses made available to the region since late 2024, estimating the country specific impact of one-time mass vaccination strategies is crucial for ongoing outbreaks and for other countries at future risk.
Methods
We adapted a next generation matrix model to incorporate vaccination which was calibrated using mpox datasets from the Democratic Republic of Congo. We projected the effective reproduction number, R eff , for 47 sub-Saharan countries from 2025 to 2050 under four transmission scenarios with different contributions of community vs sexual contacts, informed by Clade Ia and Ib outbreaks. We then calculated country-specific minimum vaccine coverages required for outbreak control and evaluated one-time age-specific mass vaccination strategies for reducing R eff .
Findings
For all 47 countries, R eff s are projected to rise. At least 20 are estimated to require vaccination in 2025, and 36 in 2050, in the event of national outbreaks. For eleven clade I-affected countries, the minimum required coverage is estimated to range from 0%–4.8% to 14.5%–19.5% in 2025 with increasing sexual transmission, increasing to 0%–10.8% and 22.6%–26.0% in 2050, respectively. The prioritised age group for vaccination shifts from 0–4 to 20–29 with additional sexual transmission.
Interpretation
With diminishing smallpox-vaccination-induced immunity, increasing R eff s and potential for persistent outbreaks are expected for mpox. Policymakers may face increasing vaccine demand, which will necessitate coordinated efforts to prioritise high-risk groups under supply constraints.
