Background: Substantial 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. Methods: For 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. Findings: Overall, 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. Interpretation: Our 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.

Estimated yellow fever vaccination coverage for at-risk districts from 1970 to 2016Estimated yellow fever vaccination coverage for the beginning of each decade from 1970 to 2016, and the number of individuals still requiring vaccination in 2016, for each district classified as endemic or low risk for yellow fever. Vaccination coverage was calculated using three alternative vaccination-targeting scenarios: targeted; untargeted, unbiased; and untargeted, biased. Full details are provided in the manuscript.number_to_vaccinate&coverage_endemic&low_risk_1970_2016.csvBias correction termsBias correction terms for each country and year applied to yellow fever vaccination data not derived from post-campaign surveys. These were calculated as ratios of survey-derived Global Burden of Disease Study estimates of mean coverage for third dose of diphtheria-tetanus-pertussis-containing vaccine (DTP3) and WHO/UNICEF Joint Reporting Process administratively reported estimates. Full details are provided in the manuscript.dtp3_bias_terms.csv