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☆
Introduction
Between 1978 and 2003, 26,667 cases and 5381 deaths due to acute encephalitis have been reported in Nepal [1]. Mortality and long-term sequellae rates are high in the age group below 15 years [2]. Although Nepal health authorities favored protecting the population by administering JE vaccines, budgetary constraints made it impossible to implement an immunization program. The donation in 1999 of a large quantity of SA14-14-2 live-attenuated JE vaccine (live JE vaccine) offered an opportunity to provide for some of those needs and to evaluate efficacy [3].
During 11–24 July 1999, nearly 160,000 doses of live JE vaccine were administered to children, ages 1–15 years, resident in 3 districts of Nepal [2], [3]. In Bardiya district 79.9% of children in this age group were vaccinated, 34% in Banke and 18% in Kailai districts. When measured during the year of administration, the efficacy of a single dose of JE vaccine was 99.26% (CI 94.9–100%) while 1 year later it was 98.5% (CI 90.1–99.2%) [3], [4]. Here we report vaccine efficacy observed after 5 years of seasonal exposure.
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Study locations and subjects
Using methods described previously [3], [4], a case–control study was performed in Nepalese children, adolescents and young adults, ages 6–20 years, residents in Bardiya district. Controls were selected from individuals of the same sex and ages living in the same village as JE cases. Study protocols were submitted to Nepal Health Research Council in November 2004 for approval of this case–control study. Because of the Maoist insurgency in Nepal, interview of controls was initiated in
JE situation and vaccination status
In 2004, from all of Nepal, 1543 cases and 131 deaths (9.8% CFR) of acute encephalitis were reported to the Epidemiology and Disease Control Division (EDCD) of the Ministry of Health, Nepal. One hundred and eleven cases were residents of Bardiya district where the administration of live JE vaccine in 1999 was reported to be 80% [1], [12], [13]. No other JE vaccine had been administered in this district by means of an organized campaign.
Case–control study
During the 2004 outbreak, 20 cases admitted to Bardiya and
Discussion
Fortuitously, the high immunization rate in Bardiya district in 1999 led to a decision by Nepalese health authorities to omit this district from participation in the killed JE vaccine campaign of 2000. Teams visiting villages to enroll control subjects found that most householders vividly remembered the 1999 immunization campaign, particularly because it was followed almost immediately by an unusually large JE epidemic and the effectiveness of SA14-14-2 vaccine was immediately apparent to a
Acknowledgements
We wish to thank Dr. Durga Pradhan, pediatrician, and Ms. Bhunu Shah, Project Nurse at the Bheri Zonal hospital, Nepalgunj and Dr. Arjun Shrestha, physician and Ms. Devi Thapa, Project Nurse at Bardiya hospital for care and identification of JE cases. Thanks also for the laboratory technical assistance of Mr. Govinda Paudel and Mr. Gyanendra, laboratory technicians, respectively at the Bheri Zonal and Bardiya hospitals. Our appreciation for the support of Dr. Yam Bahaur Basnet, Medical
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This research was supported by grants from Glovax Company Limited.
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