Japanese encephalitis
Japanese encephalitis (JE) is the main cause of viral encephalitis in many countries of Asia. The infection is mosquito-borne and caused by a virus, related to dengue, yellow fever and West Nile viruses. The virus exists in a transmission cycle between mosquitoes and pigs and/or water birds. Humans, become infected only incidentally when bitten by an infected mosquito and the disease is predominantly found in rural and periurban settings.
The disease is endemic with seasonal distribution in parts of China, the Russian Federation’s south-east, and South and South-East Asia. Estimated annual mortality ranges from 10-15,000 deaths, while the total number of clinical cases may be 50,000. Of these cases, about 50% result in permanent neuropsychiatric sequelae. The spread of JE in new areas has been correlated with agricultural development and intensive rice cultivation supported by irrigation programmes.
JE vaccines have been available since decades and have proven their potential to control the disease. Other control measures such as mosquito control or amplifying pig control have shown to be less reliable.
Until recently the most used vaccine was a purified inactivated product made from either Nakayama or Beijing strains propagated in mouse-brain tissue. The live attenuated SA14-14-2 vaccine manufactured in China has now become the most widely used vaccine in endemic countries. More recently, cell culture based inactivated vaccines have been licensed in Western countries (traveler's market) and Japan (paediatric indication). In addition, a live, recombinant vaccine based on the yellow fever vaccine strain has been submitted for license as paediatric vaccine in endemic countries.
WHO position papers
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WHO position paper on Japanese Encephalitis (August 2006)
pdf, 196kb -
Arabic translation
pdf, 157kb -
References for WHO position paper on Japanese encephalitis (August 2006)
pdf, 142kb
Further information
- Vaccine safety
- Vaccine research and development
- New and Under-utilized Vaccines Implementation (NUVI)
Last updated: 11 November 2009