Abstract
Japanese encephalitis virus (JEV) is a major cause of neurological disability in Asia and causes thousands of severe encephalitis cases and deaths each year. Although Japanese encephalitis (JE) is a WHO reportable disease, cases and deaths are significantly underreported and the true burden of the disease is not well understood in most endemic countries. Here, we first conducted a spatial analysis of the risk factors associated with JE to identify the areas suitable for sustained JEV transmission and the size of the population living in at-risk areas. We then estimated the force of infection (FOI) for JE-endemic countries from age-specific incidence data. Estimates of the susceptible population size and the current FOI were then used to estimate the JE burden from 2010 to 2019, as well as the impact of vaccination. Overall, 1,543.1 million (range: 1,292.6-2,019.9 million) people were estimated to live in areas suitable for endemic JEV transmission, which represents only 37.7% (range: 31.6-53.5%) of the over four billion people living in countries with endemic JEV transmission. Based on the baseline number of people at risk of infection, there were an estimated 56,847 (95% CI: 18,003-184,525) JE cases and 20,642 (95% CI: 2,252-77,204) deaths in 2019. Estimated incidence declined from 81,258 (95% CI: 25,437-273,640) cases and 29,520 (95% CI: 3,334-112,498) deaths in 2010, largely due to increases in vaccination coverage which have prevented an estimated 314,793 (95% CI: 94,566-1,049,645) cases and 114,946 (95% CI: 11,421-431,224) deaths over the past decade. India had the largest estimated JE burden in 2019, followed by Bangladesh and China. From 2010-2019, we estimate that vaccination had the largest absolute impact in China, with 204,734 (95% CI: 74,419-664,871) cases and 74,893 (95% CI: 8,989-286,239) deaths prevented, while Taiwan (91.2%) and Malaysia (80.1%) had the largest percent reductions in JE burden due to vaccination. Our estimates of the size of at-risk populations and current JE incidence highlight countries where increasing vaccination coverage could have the largest impact on reducing their JE burden.
Highlights
Japanese encephalitis virus (JEV) is a mosquito-transmitted flavivirus that is endemic in a large portion of South and Southeast Asia, as well as parts of the Western Pacific
1,543.1 million people are estimated to live in an area suitable for endemic JEV transmission (Fig 1)
This represents 37.7% of the 4,095.5 million people living in countries with endemic JEV transmission
Summary
Japanese encephalitis virus (JEV) is a mosquito-transmitted flavivirus that is endemic in a large portion of South and Southeast Asia, as well as parts of the Western Pacific. Previous estimates have suggested that over three billion people live in countries with JEV transmission, resulting in an estimated 68,000 clinical cases and over 13,000 deaths annually [1]. Several countries that formerly had a high burden of JE, such as Japan, Taiwan, and South Korea, have reduced that burden to almost zero mainly through high vaccination coverage [2]. These successes suggest that vaccination does not remove the zoonotic source of JEV transmission, spillover to humans can be significantly reduced via large-scale vaccination. Because local transmission to humans requires environmental conditions capable of sustaining an enzootic cycle, or at least sporadic zoonotic outbreaks that can spillover to humans, the risk of infection can vary substantially within each endemic country
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