The impact of geographic targeting of oral cholera vaccination in sub-Saharan Africa: a modeling study
BackgroundIn May 2018, the World Health Assembly committed to reducing worldwide cholera deaths by 90% by 2030. Oral cholera vaccine (OCV) plays a key role in reducing the near-term risk of cholera, although global supplies are limited. Characterizing the potential impact and cost-effectiveness of mass OCV deployment strategies is critical for setting expectations and developing cholera control plans that maximize chances of success. Methods and FindingsWe compared the projected impacts of vaccination campaigns across sub-Saharan Africa from 2018 through 2030 when targeting geographically according to historical cholera burden and risk factors. We assessed the number of averted cases, deaths, disability-adjusted life-years, and cost-effectiveness with models that account for direct and indirect vaccine effects and population projections over time. Under current vaccine supply projections, an approach optimized to targeting by historical burden is projected to avert 828,971 (95% CI: 803,370-859,980) cases (equivalent to 34.0% of projected cases; 95% CI: 33.2-34.8). An approach that balances logistical feasibility with targeting historical burden is projected to avert 617,424 (95% CI: 599,150-643,891) cases. In contrast, approaches optimized for targeting locations with limited access to water and sanitation are projected to avert 273,939 (95% CI: 270,319-277,002) and 109,817 (95% CI: 103,735-114,110) cases, respectively. We find that the most logistically feasible targeting strategy costs $1,843 (95% CI: 1,328-14,312) per DALY averted during this period and that effective geographic targeting of OCV campaigns can have a greater impact on cost-effectiveness than improvements to vaccine efficacy and moderate increases in coverage. Although our modeling approach did not project annual changes in baseline cholera risk or incorporate immunity from natural cholera infection, our estimates of the relative performance of different vaccination strategies should be robust to these factors. ConclusionsOur study suggests that geographic targeting is critical to the cost-effectiveness and impact of oral cholera vaccination campaigns. Districts with the poorest access to improved water and sanitation are not the same as districts with the greatest historical cholera incidence. While OCV campaigns can improve cholera control in the near-term, without rapid progress in developing water and sanitation services, our results suggest that vaccine use alone are unlikely to allow us to achieve the 2030 goals.