Epidemiology and risk factors of Japanese encephalitis in Taiwan, 2010–2022

• Published in: PLoS neglected tropical diseases Vol. 17; no. 10; p. e0011421
• Main Authors: Hsu, Jen-Yu, Hung, Chien-Ching, Tsou, Tsung-Pei, Chen, Wan-Chin
• Format: Journal Article
• Language: English
• Published: San Francisco Public Library of Science 02.10.2023; Public Library of Science (PLoS)
• Subjects: Agriculture; Animal husbandry; Biology and Life Sciences; Children; Confidence intervals; Disease control; Encephalitis; Epidemiology; Fishing; Forestry; Immunization; Medicine and Health Sciences; Mortality; Mosquitoes; People and Places; Risk factors; Risk groups; Seroconversion; Statistics; Vaccination; Vaccines; Vector-borne diseases; Vital statistics; Taiwan
• DOI: 10.1371/journal.pntd.0011421
• ISSN: 1935-2735; 1935-2727

Introduction Taiwan introduced a two-dose inactivated Japanese encephalitis (JE) mouse brain-derived (JE-MB) vaccine into routine childhood immunization in 1968, with booster vaccination implemented in 1974 and 1983. In 2017, JE-MB vaccine was replaced by a two-dose live-attenuated chimeric vaccine (JE-CV). After implementation of JE vaccination programs, JE cases have shifted from children to adults. In this study, we described the JE epidemiology and identify high-risk groups to further inform vaccine policy. Methodology/Principal findings We extracted data from Taiwan's notifiable disease surveillance database, vital statistics, and employment statistics from 2010 to 2022. Diagnosis of JE was confirmed by JE seroconversion, a four-fold increase in virus-specific antibodies, a positive JE viral nucleic-acid test, or JE virus isolation. From 2010 to 2022, a total of 313 cases of JE were diagnosed, resulting in an overall incidence rate of 0.10 cases per 100,000 person-years and a mortality rate of 0.006 per 100,000 population per year. Among these patients, 64% were male, and the median age was 51 years (range 0-82). Compared with people born in or after 1976 (vaccinated with four doses of JE-MB vaccine or two doses of JE-CV), those born in or before 1962 (unvaccinated) and those born during 1963-1975 (vaccinated with two or three doses of JE-MB vaccine) had a 4.2-fold (95% confidence interval [CI] 3.0-5.7) and 5.9-fold (95% CI 4.3-8.1) higher risk of JE, respectively. The relative risk of working in agriculture, forestry, fishing, or animal husbandry, compared to other occupations, was 5.0 (95% CI 3.5-7.0). Conclusions/Significance In Taiwan, individuals born before 1976 and those employed in agriculture, forestry, fishing, or animal husbandry had a higher risk of JE. We recommend JE vaccination for people in these high-risk groups who have not been fully vaccinated or have an unknown vaccination history.