Understanding MPXV Viral Clearance, Transmission Dynamics, and Mpox Vaccine Effectiveness in West Africa : Guinea

A new outbreak of clade 2b Monkeypox virus (MPXV) was first documented in Guinea in September 2024. This outbreak has a great potential to spread through intimate contact and sexual activity. The public health response to date has focused on reporting and isolation of confirmed cases, contact tracing and testing. In 2025, a donation of the JYNNEOS (modified vaccinia Ankara-Bavaria Nordic; MVA-BN) vaccine was provided to Guinea. It is a live attenuated vaccine licensed as a two-dose vaccine for prevention of Mpox infection. Due to limited vaccine supplies, many governments in West Africa have focused on giving out one dose of the vaccine to individuals at risk.

There is a dearth of information regarding transmission dynamics for clade 2b and vaccine effectiveness in endemic settings in West Africa, in populations with a high prevalence of other comorbidities and infections such as malaria. Given the current mpox outbreak's public health significance for Guinea, there is a need for comprehensive research in this endemic setting to better understand disease pathogenesis, transmission dynamics and effective control and prevention measures for clade 2b outbreaks. We have an opportunity to conduct this key research now to inform the public health measures for the current Guinea Mpox outbreak.

This study has three linked objectives to address the public health challenge of Mpox in Guinea. Objective 1 (MOVIE-West Africa) focuses on understanding the kinetics of viral elimination, shedding light on how MPXV interacts with host tissues and immune defense, and informing endpoint selection for therapeutic trials. This is important because currently there are significant data gaps in MPXV viral dynamics and transmission patterns to inform control measures for clade 1a and clade 2b in endemic settings. There are no data regarding the dynamics of viral clearance in clade 2b cases from endemic countries in West Africa. Understanding the kinetics of viral clearance is crucial for advising the Guinea government and other countries on clinical management practice and the duration of isolation protocols.

Objective 2 (TRACE-West Africa) aims to determine the secondary attack rate (SAR), assessing host susceptibility and offering vital data to target interventions towards vulnerable groups and informing vaccine efforts by contributing to the assessment of vaccine efficacy endpoints. Understanding the SAR has important implications for controlling the outbreak. By quantifying the risk of secondary transmission, SAR data can guide decisions on the prioritization of contact tracing efforts, deployment of healthcare personnel, distribution of medical supplies to mitigate further infections and inform development and adjustment of isolation and quarantine policies. High SAR values suggest a greater likelihood of secondary transmission, prompting stricter isolation measures and longer quarantine periods for contacts of mpox cases. Conversely, low SAR values may indicate that existing control measures are effective, allowing for more targeted interventions.

Objective 3 (VE-West Africa) examines the vaccine effectiveness of the MVA-BN vaccine in protection against MPXV infection and Mpox disease. The JYNNEOS vaccine is recommended as a prophylactic two-dose regimen for maximum protection against MPXV infection. Given the limited global vaccine supply, the country has taken a decision to proceed with an alternative one-dose schedule for at-risk individuals. This study will use the opportunity to measure MVA-BN vaccine effectiveness against clade 2b, the first time that this is being conducted in a clade 2b Mpox endemic country in sub-Saharan Africa. Importantly, our SAR data will be instrumental for this third objective and for future vaccine efficacy trials and vaccination campaigns and will help guide decisions on the deployment and prioritization of vaccines in Mpox outbreaks.

The MOVIE-TRACE-West Africa study will generate comprehensive evidence on clade 2b MPXV viral clearance, transmission pattern and vaccine effectiveness to guide rapid response and control policies in Guinea and other Mpox affected countries.