Assessing Mpox immune impact through a gender-structured immunization strategy under limited resources: A case study in the U.S., 2022–2023

Vaccination played a crucial role in controlling the 2022–2023 Mpox outbreak. However, existing models-typically based on constant or time-varying vaccination rates-often overlook key factors such as limited vaccine supply and gender-specific vaccination preferences, both of which were critical during this outbreak. To address these gaps, we developed a gender-structured Susceptible–Exposed–Infectious–Recovered (SEIR) model, excluding public mitigation measures, to examine the impact of constrained vaccine availability and gender-based vaccination strategies in the U.S. We first analyzed the epidemic dynamics without vaccination and then introduced an optimal gender-based vaccination strategy formulated as an isoperimetric optimal control problem. We derived the basic reproduction number, epidemic final size, and an analytical solution for the optimal control strategy under total vaccine constraints. Our results show that, without public health interventions, achieving the observed outbreak size would have required 2.628 times the actual vaccine doses administered. This highlights the equivalent effect of public health measures as increasing vaccine supply by a factor of 1.628. Sensitivity analysis further indicates that a 91.4% male vaccination rate was key to controlling the outbreak. These findings offer critical insights for future Mpox outbreaks and other emerging infectious diseases.