Assessing the impact of vaccination and behavioural change on Mpox transmission in high-risk groups in the Democratic Republic of Congo using an age-structured mathematical model

Mpox is a viral zoonotic disease that has gained global attention due to its recurrent outbreaks in endemic regions of Africa and beyond. The recent clade I outbreak in the Democratic Republic of the Congo (DRC) has been characterized by extensive transmission among children - particularly those under 15 years of age - and adults with elevated occupational risks, such as healthcare workers, sex workers, and hunters. Motivated by emerging evidence that vaccination alone may not explain the observed decline in mpox transmission across the DRC, and recognizing that behavioural modification is more feasible among adults, this study investigates the synergistic impact of vaccination and behaviour-driven contact reduction among high-risk adults within an age- and risk-structured modelling framework. The model stratifies the population into adults (high- and low-risk groups) and children. It incorporates vaccination for both adults and children, as well as behavioural adaptations (in the form of contact reduction) among high-risk adults. The model is calibrated to weekly reported mpox cases in the DRC from January 2024 to April 2025, from which key parameters are estimated. Scenario analyses reveal that among the adult population, behavioural change has a greater impact than vaccination in reducing mpox transmission. The model indicated that vaccination targeting children yielded the most significant effects, in comparison to either contact-reduction measures or immunization of adults. Moreover, our results indicate that initiating a 50% reduction in contact rates among high-risk adults approximately 20 weeks earlier yields an additional 20% decrease in the cumulative number of mpox cases, compared with implementing the same reduction concurrently with the vaccination intervention in the DRC. Given the current low vaccination coverage and supply constraints, our findings provide evidence-based guidance for optimizing vaccine allocation and prioritizing behavioural interventions among high-risk groups to prevent sustained transmission.