Targeted vaccination is effective for mpox clade Ib in England despite increased household transmission: Predictions from a modelling study.

Mpox is an emerging infectious disease with increasing global relevance. In 2024, a new clade, mpox clade Ib, was associated with high household attack rates and case fatality, raising concerns about sustained human-to-human transmission outside endemic areas. We developed and applied an individual-based probabilistic framework for mpox incorporating sexual and household contact patterns using data from the National Survey of Sexual Attitudes and Lifestyles 3 (NATSAL3). Individual and population-level reproduction numbers were estimated using setting-specific secondary attack rates. Vaccination impact was assessed across scenarios varying household attack rates, vaccine effectiveness, and distribution strategies. We predict that fewer than 3 out of 100 individuals generated more than one secondary case of clade Ib in England, with a population reproduction number of 0.69 (95%CI 0.66 - 0.71). Individuals reporting both same-sex and opposite sexual contact disproportionately contributed to transmission potential. Increasing household secondary attack rates led to modest increases in the population reproduction number due to individuals with the highest reproduction numbers having lower than average numbers of household contacts. Targeted vaccination, focused on individuals with higher numbers of sexual contacts, consistently outperformed non-targeted strategies, requiring lower vaccine coverage to achieve control even under elevated household transmission. Vaccine effectiveness against infection and onward transmission critically influenced the success of vaccination programs. Despite higher household transmission risks, targeted vaccination remains an effective strategy for controlling mpox clade Ib in England. Transmission dynamics are strongly shaped by underlying contact structures, emphasizing the importance of network-informed interventions. Rapid, network-informed models can provide valuable early guidance for emerging infectious diseases.