Our clade I mpox paper is now out in Nature Health
Published:
Our clade I mpox paper is now out in Nature Health! Co-led by Akira Endo, Toshiaki R. Asakura and me, we used age- and sex-specific contact models to quantify the roles of community and sexual contacts in clade Ia vs Ib transmission in DRC and Burundi.
Link: https://doi.org/10.1038/s44360-026-00080-7
Clade Ia MPXV historically circulated in DRC mainly through zoonotic spillover followed by limited human-to-human transmission. In contrast, the rapid growth of clade Ib, first identified in South Kivu, DRC in 2024, suggested sustained human-to-human transmission.
Although early investigations of the clade Ib outbreak identified heterosexual contacts involving female sex workers (FSWs) and clients as key exposure routes, community contacts may also have contributed, with children accounting for a substantial share of reported cases.
To assess the relative contribution of community and sexual contact transmission, we modelled age- and sex-dependent contact patterns to explain the observed age/sex profiles of clade Ia and Ib cases.
Summary
We first reproduced the age distribution of historical clade Ia cases in Tshuapa, DRC (2011-2015), accounting for contact patterns across age groups and age-dependent relative susceptibility: higher in young children and lower in older, smallpox-immunised cohorts.
This model also reproduced the 2024 age distribution of clade Ia cases in endemic provinces, suggesting those outbreaks were primarily driven by community contacts.
Using the same age-dependent susceptibility estimates, we then extended the model to include sexual contact transmission and fitted it to clade Ib data, resulting in a better explanation of the excess cases in sexually active age groups.
Our estimates suggest that sexual contact contributed 42% of clade Ib transmission in the Kivus overall, consistent with an increased reproduction number of around 1.5 for clade Ib in the Kivus versus around 0.90 for clade Ia in endemic provinces with limited sexual contact contribution.
As with the 2022 clade IIb outbreak predominantly spreading among MSM, clade Ib may have found its niche in another key population group, FSWs. Our findings reinforce the importance of supporting key populations for mpox control.
Finally, huge thanks to all co-authors!
