Japanese encephalitis in Nepal: closing the adult immunity gap.

Japanese encephalitis (JE) in Nepal is undergoing an epidemiological shift from a predominantly pediatric, Terai-centered disease to a geographically broader threat affecting susceptible adults. Despite successful childhood vaccination, the 2025 resurgence, with 175 confirmed cases and 34 deaths, exposed a major immunity gap among older cohorts, particularly adults over 40 years. Expanding transmission into hill districts and higher-altitude areas, likely influenced by climate variability, land-use change, and vector ecology, further challenges existing control strategies. Because JE overlaps clinically and radiologically with other endemic encephalitides, rapid laboratory confirmation is essential. Nepal's emerging adult vaccination policy should be integrated with climate-informed surveillance, One Health data systems, vector control, and survivor rehabilitation before future monsoon-driven outbreaks.