Abstract
BackgroundTo counter the increasing global risk of Yellow fever (YF), the World Health Organisation initiated the Eliminate Yellow fever Epidemics (EYE) strategy. Estimating YF burden, as well as vaccine impact, while accounting for the features of urban YF transmission such as indirect benefits of vaccination, is key to informing this strategy.Methods and findingsWe developed two model variants to estimate YF burden in sub-Saharan Africa, assuming all infections stem from either the sylvatic or the urban cycle of the disease. Both relied on an ecological niche model fitted to the local presence of any YF reported event in 34 African countries. We calibrated under-reporting using independent estimates of transmission intensity provided by 12 serological surveys performed in 11 countries. We calculated local numbers of YF infections, deaths and disability-adjusted life years (DALYs) lost based on estimated transmission intensity while accounting for time-varying vaccination coverage. We estimated vaccine demand and impact of future preventive mass vaccination campaigns (PMVCs) according to various vaccination scenarios.Vaccination activities conducted in Africa between 2005 and 2017 were estimated to prevent from 3.3 (95% CI 1.2–7.7) to 6.1 (95% CI 2.4–13.2) millions of deaths over the lifetime of vaccinees, representing extreme scenarios of none or maximal herd effects, respectively. By prioritizing provinces based on the risk of urban YF transmission in future PMVCs, an average of 37.7 million annual doses for PMVCs over eight years would avert an estimated 9,900,000 (95% CI 7,000,000–13,400,000) infections and 480,000 (180,000–1,140,000) deaths over the lifetime of vaccinees, corresponding to 1.7 (0.7–4.1) deaths averted per 1,000 vaccine doses.ConclusionsBy estimating YF burden and vaccine impact over a range of spatial and temporal scales, while accounting for the specificity of urban transmission, our model can be used to inform the current EYE strategy.
Highlights
Recent outbreaks in Angola, Nigeria and Brazil have shown that yellow fever (YF) remains a significant public health threat [1,2]
By prioritizing provinces based on the risk of urban YF transmission in future preventive mass vaccination campaigns (PMVCs), an average of 37.7 million annual doses for PMVCs over eight years would avert an estimated 9,900,000 infections and 480,000 (180,000–1,140,000) deaths over the lifetime of vaccinees, corresponding to 1.7 (0.7–4.1) deaths averted per 1,000 vaccine doses
By estimating YF burden and vaccine impact over a range of spatial and temporal scales, while accounting for the specificity of urban transmission, our model can be used to inform the current Eliminate Yellow fever Epidemics (EYE) strategy
Summary
Recent outbreaks in Angola, Nigeria and Brazil have shown that yellow fever (YF) remains a significant public health threat [1,2]. The spread of YF to Asia, where the virus has not yet been detected despite the presence of competent vectors, could have a major negative public health impact [3,4]. In 2016, the World Health Organisation (WHO) adopted a strategy to Eliminate Yellow fever Epidemics (EYE) by 2026. This strategy aims to prevent sporadic cases sparking urban outbreaks, minimizing the risk of international spread [5]. Estimating YF burden, as well as vaccine impact, while accounting for the features of urban YF transmission such as indirect benefits of vaccination, is key to informing this strategy.
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