Mpox Outbreak 2022: A Comparative Analysis of the Characteristics of Individuals Receiving MVA-BN Vaccination and People Diagnosed with Mpox Infection in Milan, Italy.

Mpox caused a worldwide outbreak in 2022, disproportionately affecting MSM reporting high-risk sexual behaviors. The aim of this study was to compare the characteristics of people receiving MVA-BN vaccination with those of individuals diagnosed with mpox to guide future vaccination policies. This was a retrospective study on people with mpox infection or vaccination at San Raffaele Scientific Institute, Milan, Italy, from May to November 2022. Characteristics were compared using Mann-Whitney or chi-square/Fisher's exact tests; multivariable logistic regression and classification tree analysis were applied. Overall, 473 vaccinated individuals and 135 with mpox were included; 472/473 and 134/135 were MSM. People with mpox were more frequently living with HIV (48.9% vs. 22.4%, p < 0.001), had ≥1 previous STI (75.6% vs. 35.7%, p < 0.001), were chemsex users (37.8% vs. 6.34%, p < 0.001), were with a higher number of partners (23.0% vs. 1.69%, p < 0.001), and had engaged in group sex (55.6% vs. 24.1%, p < 0.001). At multivariable analysis, PLWH (aOR = 2.86, 95%CI = 1.59-5.19, p < 0.001), chemsex users (aOR = 2.96, 95%CI = 1.52-5.79, p = 0.001), those with previous syphilis (aOR = 4.11, 95%CI = 2.22-7.72, p < 0.001), and those with >10 partners (aOR = 11.56, 95%CI = 6.60-21.09, p < 0.001) had a higher risk of infection. This study underscores the importance of prioritizing MSM with prior STIs and multiple partners as well as chemsex users in vaccination policies to curb mpox spread. A destigmatized assessment of sexual history is vital for comprehensive sexual health strategies.