More effective meningitis vaccination campaigns using weather information over Africa

Using earlier-established relationships between humidity and the likelihood of meningitis epidemics, we retrospectively assessed the benefits of Thorpex Tigge ensemble weather forecasts to inform more effective allocation of scarce reactive vaccine around the end of the African meningitis season. Results (with caveats) conclude that potentially millions of dollars could have been saved.

Meningitis epidemics in the Sahel have historically occurred with regularity, leading to the deaths of hundreds. Until 2010, the protection provided by the only available vaccine was so limited and short-lived that the only practical strategy for vaccination was reactive: waiting until an epidemic occurred in the region and then vaccinating in that region to prevent the epidemic's further growth. While a new vaccine has recently been developed that is effective and inexpensive enough to be used more broadly and proactively, it is only effective against serogroup A which causes the most common kind of bacterial meningitis in the Sahel. As a result, there will likely be continued need for reactive vaccination strategies as new serogroups continue to circulate..

Because the reactive vaccine only provides protection for two to three years, does not prevent carriage, and does not induce herd immunity, retrospective analysis can estimate the impact of meningitis on a district with or without a reactive vaccination campaign and with or without advanced knowledge of weather conditions. This approach allows us to retrospectively assess how “perfect” weather information during the end of the meningitis season could have been used to allow public health officials to deploy vaccines sooner to areas in which the epidemics are likely to persist due to continued dryness and avoid vaccinating areas where the epidemics will end with higher humidity, mitigating the impact of the disease on human morbidity, mortality, and strained health-directed financial resources. However, in reality no forecast is perfect, and often ensemble approaches are the best option. In this context we tested the application and skill of the Thorpex Tigge multi-center ensemble weather forecasts. In this talk we discuss the algorithm used to optimally blend the multi-model ensemble weather forecasts, and discuss the benefits of its application to more effectively allocate scare meningitis vaccine over single-model or climate forecasts. We also discuss the weekly World Health Organization exercise held during the 2011-2013 meningitis seasons designed to provide and test the utility of country-specific forecasts in helping inform public health officials from several African countries during the vaccination decision-making process, along with the decision-information tool developed for use during this exercise.