Global yellow fever vaccination coverage from 1970 to 2016: an adjusted retrospective analysis

Abstract

SummaryBackgroundSubstantial outbreaks of yellow fever in Angola and Brazil in the past 2 years, combined with global shortages in vaccine stockpiles, highlight a pressing need to assess present control strategies. The aims of this study were to estimate global yellow fever vaccination coverage from 1970 through to 2016 at high spatial resolution and to calculate the number of individuals still requiring vaccination to reach population coverage thresholds for outbreak prevention.MethodsFor this adjusted retrospective analysis, we compiled data from a range of sources (eg, WHO reports and health-service-provider registeries) reporting on yellow fever vaccination activities between May 1, 1939, and Oct 29, 2016. To account for uncertainty in how vaccine campaigns were targeted, we calculated three population coverage values to encompass alternative scenarios. We combined these data with demographic information and tracked vaccination coverage through time to estimate the proportion of the population who had ever received a yellow fever vaccine for each second level administrative division across countries at risk of yellow fever virus transmission from 1970 to 2016.FindingsOverall, substantial increases in vaccine coverage have occurred since 1970, but notable gaps still exist in contemporary coverage within yellow fever risk zones. We estimate that between 393·7 million and 472·9 million people still require vaccination in areas at risk of yellow fever virus transmission to achieve the 80% population coverage threshold recommended by WHO; this represents between 43% and 52% of the population within yellow fever risk zones, compared with between 66% and 76% of the population who would have required vaccination in 1970.InterpretationOur results highlight important gaps in yellow fever vaccination coverage, can contribute to improved quantification of outbreak risk, and help to guide planning of future vaccination efforts and emergency stockpiling.FundingThe Rhodes Trust, Bill & Melinda Gates Foundation, the Wellcome Trust, the National Library of Medicine of the National Institutes of Health, the European Union's Horizon 2020 research and innovation programme.

Genomic and epidemiological monitoring of yellow fever virus transmission potential

“…Yellow fever (YF) is an acute viral hemorrhagic disease responsible for 29000-60000 deaths annually in South America and Africa (1) and is the most severe mosquito-borne infection in the tropics (2). Despite the existence of a highly effective YF vaccine since 1937, an estimated >400 million unvaccinated people live in areas at risk of infection (3). Yellow fever virus (YFV) is a member of the Flaviviridae family and is classified into four genotypes: East African, West African, South American I, and South American II (4)(5)(6)(7)(8).…”

The Impact and Control of Emerging and Re-Emerging Viral Diseases in the Environment: An African Perspective

“…There have been occasional issues of supply and demand, as experienced in Angola and Democratic Republic of Congo in 2016 (Barrett 2017). Inadequate vaccine coverage is also a problem in many countries where the disease is endemic (Shearer et al 2017).…”

Mosquito and primate ecology predict human risk of yellow fever virus spillover in Brazil

“…1), assuming that biting rate and reservoir infection prevalence are constant over space and time in the absence of empirical data on these parameters, as described in Table 1. Second, we define immunological-environmental risk as environmental risk multiplied by the estimated proportion of the human population that is susceptible to yellow fever, using previously estimated vaccine coverage rates (17). Third, we define population-scaled risk as the immunological-environmental risk scaled by the number of people in a given location.…”

“…Additional details on mechanistic model methods and data are available in the Supplementary Materials. For primate distribution, human susceptibility, and human population density, we used previously published estimates (17,20,21). All other mechanistic models (terms in Eq.…”