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

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.

背景：过去两年，安哥拉与巴西暴发大规模黄热病（yellow fever）疫情，叠加全球疫苗储备短缺的现状，凸显了评估当前黄热病防控策略的迫切需求。本研究旨在以高空间分辨率估算1970年至2016年的全球黄热病疫苗接种覆盖率，并计算为达到疫情暴发预防所需的人群接种阈值，仍需接种疫苗的人群数量。

方法：本研究为调整后的回顾性分析，我们整合了1939年5月1日至2016年10月29日期间，各类来源（如世界卫生组织（WHO）报告、卫生服务提供者登记册）发布的黄热病疫苗接种活动数据。为考量疫苗接种行动目标设定的不确定性，我们计算了三种人群接种覆盖率以覆盖不同假设场景。随后将上述数据与人口统计信息相结合，并追踪随时间变化的疫苗接种覆盖率，以估算1970年至2016年间，黄热病病毒（yellow fever virus）传播风险国家内每个二级行政区中，既往接种过黄热病疫苗的人口比例。

结果：总体而言，自1970年以来疫苗覆盖率实现了显著增长，但黄热病风险区内当前的疫苗接种覆盖率仍存在显著缺口。我们估算，要达到世界卫生组织（WHO）推荐的80%人群接种阈值，黄热病病毒传播风险区内仍有3.937亿至4.729亿人需要接种疫苗；这一人群占黄热病风险区总人口的43%至52%，而1970年时需要接种疫苗的人群占比为66%至76%。

解读：本研究结果凸显了黄热病疫苗接种覆盖率存在的显著缺口，可为更精准量化疫情暴发风险提供支撑，并有助于指导未来疫苗接种工作规划与应急疫苗储备调度。