Incidence, drivers and global health implications of the 2019/2020 yellow fever sporadic outbreaks in Sub-Saharan Africa

Abstract

The 2019 and 2020 sporadic outbreaks of Yellow fever (YF) in Sub-Saharan Africa (SSA) countries had raised a lot of global health concerns. This article aims to narratively review the vector biology, YF vaccination program, environmental factors and climatic changes, and to understand how they could facilitate the re-emergence of YF. This study comprehensively reviewed articles that focused on the interplay and complexity of YF Virus (YFV) vector diversity/competence, YF vaccine immunodynamics, and climatic changes impacts on YFV transmission as they influence the 2019/2020 sporadic outbreaks in Sub-Saharan Africa (SSA). Based on available reports, vectorial migration, climatic changes, and YF immunization level could be reasons for the re-emergence of YF at the community and national levels. Essentially, the drivers of YFV infection due to spillover are moderately constant. However, changes in land use and landscape have been shown to influence sylvan-to-urban spillover. Furthermore, increased precipitation and warmer temperatures due to climate change, are likely to broaden the range of mosquitoes' habitat. The 2019/2020 YF outbreaks in SSA is basically a result of inadequate vaccination campaigns, YF surveillance and vector control. Consequently, and most importantly, adequate immunization coverage must be implemented and properly achieved under the responsibility of the public health stakeholders.

A proposed One Health approach to control yellow fever outbreaks in Uganda

“…In the human domain, human activities and susceptibility due inadequate acquired immunity contribute to the sustained occurrence of YF [28,29]. For instance, research revealed that changes in land use may influence the shift from sylvatic-to-urban YF transmission cycles [30].…”

“…The environmental factors encompass climate and seasonal temperature variation, changes in urbanization and land use, and vector population distribution. Important environmental and bioclimatic data have demonstrated that prevalence of zoonotic diseases is both sustained and exacerbated by shifts in average temperature, total annual precipitation, and relative humidity [30,34,35]. The rise in precipitation and warmer temperatures likely expanded mosquito populations in affected regions [30].…”

“…Important environmental and bioclimatic data have demonstrated that prevalence of zoonotic diseases is both sustained and exacerbated by shifts in average temperature, total annual precipitation, and relative humidity [30,34,35]. The rise in precipitation and warmer temperatures likely expanded mosquito populations in affected regions [30]. Furthermore, the environmental preference of mosquitoes determines the nature of the outbreak.…”

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“…Reoccurring YF cases involving sylvatic cycles have been described in Brazil since 2016 [3][4][5][6]. Furthermore, outbreaks based on urban cycles were reported in Sub-Saharan African countries in 2019 and 2020 [7][8][9]. While YF is absent in the Asia-Pacific region, Dengue occurs in the Asia-Pacific region as well as Africa, the Americas, and the Eastern Mediterranean with Asia representing about 70% of the global burden of disease [10][11][12].…”