Global Risk and Elimination of Yellow Fever Epidemics

Abstract

Background: Yellow fever (YF) is a vector-borne viral hemorrhagic disease endemic in Africa and Latin America. In 2016, the World Health Organization (WHO) developed the Eliminate YF Epidemics strategy aiming at eliminating YF epidemics by 2026.

Methods: We developed a spatiotemporal model of YF, accounting for the impact of temperature, vector distribution, and socioeconomic factors on disease transmission. We validated our model against previous estimates of YF basic reproductive number (R0). We used the model to estimate global risk of YF outbreaks and vaccination efforts needed to achieve elimination of YF epidemics.

Results: We showed that the global risk of YF outbreaks is highly heterogeneous. High-risk transmission areas (R0 > 6) are mainly found in West Africa and the Equatorial region of Latin America. We showed that vaccination coverage needed to eliminate YF epidemics in an endemic country varies substantially between districts. In many endemic countries, a 90% vaccination coverage is needed to achieve elimination. However, in some high-risk districts in Africa, a 95% coverage may be required.

Conclusions: Global elimination of YF epidemics requires higher population-level immunity than the 80% coverage recommended by the WHO. Optimal YF vaccination strategy should be tailored to the risk profile of each endemic country.

Keywords: basic reproductive number; global epidemics elimination; threshold vaccination coverage; yellow fever.