The PREGMPOX study employs a prospective cohort design enriched with a nested case-control component, adeptly tracking the dynamics of MPXV infection among pregnant women.

This approach incorporates a rigorous baseline data collection phase that enhances the understanding of initial disease presentation and risk factors associated with confirmed MPXV infection. Such detailed profiling at baseline is critical for identifying early disease characteristics and potential co-factors affecting outcomes. Further, follow-up and endline assessments are strategically planned to estimate the incidence of new infections and assess mother-child health outcomes in various groups: those testing positive versus negative for MPXV, vaccinated versus unvaccinated individuals, and comparisons between those treated with tecovirimat versus those who are not. This structured analysis allows for an in-depth evaluation of intervention effectiveness and safety. The study design also includes a test-negative case-control approach as a secondary analytical method. While not the primary focus-given the high specificity of PCR in confirming MPXV in over 90% of cases-this approach is valuable for confirming intervention effectiveness under natural conditions. This methodology is designed to avoid the ethical concerns often associated with randomized control trials in vulnerable populations, ensuring the feasibility and relevance of the study's outcomes. PREGMPOX employs a strategic combination of passive and active surveillance methods to comprehensively track the spread of MPXV among pregnant women, aiming to capture the full spectrum of the virus's impact. Passive surveillance is embedded into routine antenatal care, where healthcare providers systematically monitor and document MPXV symptoms, leveraging the existing healthcare infrastructure. This allows for the continuous collection of data within a clinical setting. In contrast, active surveillance extends beyond the confines of healthcare facilities, involving community health workers who engage directly with the community to identify and document MPXV cases that might not otherwise come to clinical attention. This includes setting up specialized screening stations that facilitate the detection of cases in non-clinical environments. This dual surveillance approach is vital due to the severe risks associated with MPXV, particularly the high rates of foetal demise linked to severe infections. By combining both surveillance strategies, PREGMPOX enhances its capability for early detection and effective response, including prompt referral for necessary interventions. This comprehensive data collection and proactive case finding strategy are crucial for implementing timely interventions that could prevent severe outcomes in pregnant women and their foetuses, thereby mitigating the broader impact of the MPXV outbreak. PREGMPOX will also contribute to basic research in this vulnerable population where data is scarce by conducting immunological and histopathological assessments to understand the mechanisms underlying the impact of MPVX infection on pregnancy. These assessments will be conducted through a nested case-control study within the larger cohort. Samples will be collected at specific time points to evaluate immune responses to MPVX infection or vaccination and to study placental pathology in infected cases.