Modeling the impact of vaccine dose prioritization strategies during the 2022 mpox outbreak

Early in the 2022 mpox outbreak, the US recommendation was to administer two doses of the JYNNEOS vaccine 4 weeks apart. However, because of limited vaccine supply, New York City (NYC) prioritized single dose vaccination. We estimated mpox cases averted by this strategy compared to strategies that prioritized 2-dose vaccination for a smaller portion of the population. We fit a network transmission model to incident mpox cases in NYC. Model output consisted of predicted cases over time when vaccine doses were administered with the "first-dose priority" strategy, compared with counterfactual simulations, where doses were administered to those eligible for a second dose ahead of those waiting for a first dose ("intermediate" strategy), or where individuals were preallocated full courses of the vaccine ("second-dose priority" strategy). We estimate that NYC's strategy averted 66% (IQR, 47%-78%) of potential mpox cases compared to no vaccination. This "first-dose priority" strategy averted 0.6% (IQR, -11% to 9.8%) more cases than the "intermediate" strategy, and 17% (IQR, 2.9%-38%) more cases than the "second-dose priority" strategy. Thus, for the 2022 mpox outbreak in NYC, preallocating vaccine doses to ensure full vaccination in a high-priority subset of the population would have increased the size of the outbreak.