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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 70,000 cases and up to 20,000 deaths each year, mostly among children under 15 years of age, despite the availability of several licensed and effective JE vaccines. 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 southern and eastern Asia, the Indian subcontinent, and southeast Russia where roughly 3 billion people, including 700 million children, are at risk for JE. Because of their proximity to mosquito-breeding environments such as rice paddies, rural populations face the greatest risk of infection.
  • An estimated 70,000 clinical cases and 13,000 to 20,000 deaths occur each year, mostly among children under 15 years old. In endemic areas, recent estimates of the annual JE incidence range from 1 to 15 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 the brain (encephalitis) and kills up to 30 percent of those who fall ill. Up to half of JE survivors are left with severe, long-term neurological damage, including paralysis and the inability to speak.
  • There is no clinical treatment for JE. Care of patients focuses on treatment of symptoms and complications.
  • Vaccination is the single most important measure to control JE, as vector control has proven ineffective.

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-2017, three JE vaccines have been prequalified by the WHO, signifying them as high-quality, safe, and immunogenic:
    • CD-JEV (also known as SA 14-14-2), a live attenuated 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 discontinuing the use of mouse brain-derived vaccines due to safety concerns, high variability of manufacturing, higher price, lower availability, need for repeated doses and boosters, and contamination with mouse proteins.

References

Page last updated: October 2017.

Photo: PATH/Aaron Joel Santos.