Benefit of vaccination in protecting the departments of Grand’Anse, Ouest and Sud against a potential second epidemic wave of cholera

In a previous report, we presented model projections based on data available up to epi-week 43 (ending Oct-29). These projections suggested that, due to anticipated heavy rainfalls at the end of November, a second peak of cholera might be observed in early December in the departments of Grand’Anse and Sud, with potential propagation to other departments. These projections supported the strategy of the MSPP 2 OCV 3 campaign to vaccinate 800,000 people in these two departments, which were also the areas most affected by damage from Hurricane Mathew in early October. Eventually, the vaccine campaign took place from 11 to 18 November but heavy rainfall was not recorded in late November and no second wave of cholera was observed. In this context, the benefits of the vaccine campaign are difficult to assess since the limited spread is likely the result of non-favourable environmental conditions and the reduction of the susceptible population thanks to the immunization campaign. Here we show that, had heavy rainfall occurred in late November and early December 2016 (as NOAA was forecasting in late October), the vaccine campaign was effectively designed to considerably reduce the risk of a second epidemic wave in Grand’Anse and Sud, with more limited effects in Ouest department.