Background: More than 30,000 cases of mpox were reported in the United States in 2022. Most of these infections were associated with sexual contact between men. Since mid-August, cases have steadily declined. Interventions to mitigate the outbreak included vaccination and a temporary reduction in sexual partnerships. Understanding the relative contributions of these interventions to decreasing daily cases can inform public health efforts in the future.
Methods: We fit a dynamic network transmission model to mpox cases reported by the District of Columbia from June 1, 2022, to January 10, 2023. This model incorporated both vaccine administration data paired with recent vaccine efficacy estimates and reductions in sexual partner acquisition by gay, bisexual, or other men who have sex with men (MSM). Our model output consisted of predicted cases diagnosed over time with or without vaccination and/or behavior change. We additionally examined model scenarios with varying vaccination timing and dose availability.
Results: We estimated that initial declines in case reports were due to reductions in sexual partnerships. One year into the outbreak, the combination of vaccination and short term, community driven reductions in sexual partnerships prevented 80% [IQR 74% - 85%] of cases that would have occurred in the absence of both interventions. Vaccination alone averted 64% [IQR 57% - 72%] of cases and behavior change alone averted 21% [IQR 11% - 29%] of cases. We estimated that administering vaccines one month earlier would have averted an additional 31% [IQR 46% - 13%] of observed cases. We further estimated that in the absence of vaccination, short term, community driven behavior change would have reduced the number of cases but would also have prolonged the outbreak.
Conclusions: We found that initial declines in daily cases were likely caused by short term, community driven behavior changes, but vaccination averted more cases overall and was key to ending the outbreak. Overall, this indicates that outreach to encourage individuals to protect themselves from infection was vital in the early stages of the mpox outbreak, but that combination with a robust mpox vaccination program was required to stop transmission.
