Considering the effects of pair formation dynamics on mpox and HIV co-infection in the gbMSM community.

The intersection of recent mpox outbreaks with HIV infections has become cause for concern in the disproportionately affected community of gay, bisexual, and other men who have sex with men (gbMSM). There is a growing need to explicitly consider how behaviour plays a role in the spread of such diseases transmitted through close, prolonged contact. In particular, the duration individuals spend single or in relationships has yet to be incorporated into deterministic co-infection models, potentially underestimating the protective effects of stable partnerships. We propose an mpox and HIV co-infection model that incorporates the formation of pairs between individuals. Through analyses of the basic ([Formula: see text]) and mpox invasion reproduction numbers ([Formula: see text]), we studied the effects of a pair formation structure on early disease dynamics in the gbMSM population. We demonstrate that considering pair formation and dissolution rates are critical in determining outbreak potential and severity, as well as accurately estimating reproduction numbers. Through simulations of the Canadian context, we show that these considerations remain important beyond the initial stages of the outbreak and can lead to more accurate predictions. Our work highlights that the particular pairing context and serological status of the population should always be carefully considered prior to intervention on behavioural patterns.