Presymptomatic transmission, vaccine breakthrough and anonymous contacts: a cluster of mpox in Canberra, Australian Capital Territory, 2024

This report outlines a localised cluster of mpox detected in July 2024, in Canberra, Australian Capital Territory. Investigation identified nine cases, including likely presymptomatic transmission by a vaccinated primary case with a high-contact profile. Five of the nine cluster cases had breakthrough infections and had received two mpox vaccinations more than 18 months earlier. The public health response involved targeted community engagement and a pop-up vaccination clinic, although a high proportion of anonymous sexual partners made contact tracing challenging. These findings underscore the potential for presymptomatic transmission and the importance of ongoing preventive measures, even with vaccination, in high-contact environments.