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Japanese encephalitis (JE)

Girl receiving an injection in her upper arm.

Japanese encephalitis (JE), the leading cause of viral encephalitis in Asia, causes an estimated 30,000 to 50,000 cases and 10,000 to 15,000 deaths each year, mostly among children under 15 years of age. There is no specific treatment for JE. Vaccination is the single most important measure for controlling the disease.

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On the PATH website

JE disease

  • JE is the leading cause of viral encephalitis in Asia and is spread by infected mosquitoes. The risk of infection is greatest in parts of southern and eastern Asia, the Indian subcontinent, and southeast Russia. Approximately 3 billion people, including 700 million children, live in areas at risk of JE. Because of their proximity to mosquito-breeding environments such as rice paddies and standing water, populations in rural areas face the greatest risk of infection.
  • An estimated 30,000 to 50,000 cases and 10,000 to 15,000 deaths occur each year, mostly among children under 15 years old. In endemic areas, the annual incidence of clinical disease ranges from 10 to 100 per 100,000 population.
  • On average, 1 in 300 infections results in symptomatic illness, which is characterized by a flu-like illness with sudden onset of fever, chills, headache, tiredness, nausea, and vomiting. The illness can progress to encephalitis (infection of the brain) and kills up to 30 percent of those who fall ill. Up to half of its survivors are left with severe, long-term neurological damage, including paralysis and the inability to speak.
  • Vaccination is the single most important measure to control JE, as vector control has proven ineffective. There is no clinical treatment for JE. Care of patients focuses on treatment of symptoms and complications.

JE vaccines

  • In areas where JE is recognized as a public health priority, the World Health Organization (WHO) recommends implementing a one-time JE vaccination campaign focused on the at-risk population followed by incorporation of JE vaccine into routine immunization.
  • As of mid-2016, three JE vaccines have been prequalified by the WHO as high-quality, safe, and immunogenic:
    • CD-JEV, a live attenuated single-strain (SA 14-14-2) JE vaccine manufactured by the Chengdu Institute of Biological Products;
    • JE-CV, a live recombinant JE vaccine manufactured by the Government Pharmaceutical Organization-Merieuk Biological Products Co., Ltd.; and
    • JEEV, an inactivated, Vero cell-derived JE vaccine manufactured by Biological E.
  • In addition to the three WHO-prequalified JE vaccines, more than ten other JE vaccines are made. All are inactivated and derived from either infected mouse brains or cell cultures. Although mouse brain-derived vaccines are effective, in 2006, WHO recommended mouse brain-derived vaccines be replaced by newer JE vaccines due to safety concerns as well as the variability of manufacturing, higher price, lower availability, and the need for repeated doses and boosters.

References

Page last updated: October 2016.

Photo: PATH/Aaron Joel Santos.