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

Early in the 2022 mpox outbreak, the U.S. 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 pre-allocated 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%-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, pre-allocating vaccine doses to ensure full vaccination in a high-priority subset of the population would have increased the size of the outbreak.