Single dose of SA 14-14-2 vaccine provides long-term protection against Japanese encephalitis: A case–control study in Nepalese children 5 years after immunization

In July 1999, a single dose of live-attenuated SA 14-14-2 Japanese encephalitis (JE) vaccine was administered to children living in the Bardiya, Banke and Kailali districts of Nepal. In 2004, the original vaccinated population experienced a fifth seasonal exposure to JE. We performed a case–control study comparing the prevalence of the administration of vaccine in patients with JE hospitalized in the Bardiya and Bheri Zonal hospitals and in age–sex matched controls resident in the Bardiya district. Among the 219 village controls, 114 had been vaccinated (52.1%) while only one of 20 JE cases had received live-attenuated JE vaccine. Five years after administration of a single dose, SA 14-14-2 provided a protective efficacy of 96.2% (CI 73.1–99.9%).