In May 2023, an increase in mpox cases was observed in Chicago, primarily among fully vaccinated individuals, prompting an investigation into the outbreak's characteristics and causes.
Researchers assessed demographic and health data from patients, analyzed viral genomes, and evaluated the humoral antibody responses to understand vaccine effectiveness and potential compromises.
Of the 49 identified cases, 57% were fully vaccinated, with findings suggesting that increased exposure through higher median numbers of sexual partners was a key factor in the outbreak, despite overall vaccine effectiveness.