1 Rationale
1.1 Background
The bacterium Vibrio cholerae was introduced to the African continent from Asia in 1967 and has since become endemic in many countries in Sub-Saharan Africa (SSA). While sporadic outbreaks have occurred each year over the past six decades, a significant surge in transmission has been observed since 2021, which is consistent with a global increase in cases and deaths during this time. This increase is likely driven by a combination of factors such as climate change, disruptions to municipal services due to conflict, population displacement, and past shortages of the Oral Cholera Vaccine (OCV). Therefore, a spatial model of endemic cholera that accounts for the many drivers of transmission and provides insights into the most impactful interventions will be a valuable tool to support cholera control.
1.2 OCV Stockpiles
Containing cholera transmission relies primarily on improvements to Water, Sanitation, and Hygiene (WASH) and the use of the OCV. However, implementing WASH improvements takes time, and in conflict-affected areas, poor infrastructure often hinders progress. As a result, OCV remains a critical tool for slowing cholera spread in both outbreak and endemic settings.
The depletion of OCV stockpiles in 2024 led to a shift toward single-dose reactive OCV strategies. Increased vaccine production by multiple manufacturers is expected to improve OCV availability in 2025 and beyond. A key question now is how best to allocate OCV through preventative campaigns to reduce transmission and support the goal of reducing cholera deaths by 90% by 2030, led by the WHO Global Task Force for Cholera Control (GTFCC). The MOSAIC framework is designed to maximize the impact of regional preventative OCV strategies by assessing country prioritization, OCV dosing schedules, and overall OCV demand.
1.3 Impacts of Climate Change
Environmental factors play a crucial role in cholera outbreaks, with extreme weather events creating local conditions that foster V. cholerae transmission. Models incorporating climate change can provide valuable insights into future cholera dynamics by accounting for environmentally forced transmission, which enables more accurate forecasts and scenarios that will contribute to achieving the GTFCC goal. The MOSAIC framework leverages Artificial Intelligence (AI) models and global climate model projections to predict climate change’s impact on cholera transmission and generate mid-term forecasts of high-risk areas across SSA.
1.4 Data and Modeling
A significant challenge in controlling cholera transmission in SSA is the lack of comprehensive data sets and dynamic models designed to support ongoing policy-making. The persistent endemic nature of cholera in SSA presents a complex quantitative challenge, requiring sophisticated models to produce meaningful inferences. Models that incorporate the necessary natural history and disease dynamics, and operate at adequate spatial and temporal scales, are crucial for providing timely and actionable information to address ongoing and future cholera outbreaks.
Although developing data and models at these scales is challenging, our goal with the MOSAIC framework is to create a landscape-scale transmission model for cholera in SSA (first at the country-level and then later at the district-level). Models are being developed with an array of historical and real-time data sources that include incidence and mortality reports, patterns of human movement, WASH, OCV campaigns, and climate variables.
Key questions we aim to address include when and where to administer a limited supply of oral cholera vaccine (OCV) and how severe weather events and climate change will impact future outbreaks. Our approach will include 5-month forecasts and long-range OCV scenarios out to 2030. Model outputs will be updated biweekly or monthly based on data availability.