Diseases and vaccines

Japanese encephalitis (JE)

To learn more about PATH's work to bring safe, effective, and affordable Japanese encephalitis vaccines to the developing world, please visit the JE Project web page.

JE disease

  • JE is the leading cause of viral encephalitis in Asia. Infection is spread by infected mosquitoes. The risk of infection is greatest in parts of southern and eastern Asia, the Indian subcontinent, and the Southeastern Russian Federation. In all areas, the risk of infection is greatest in rural areas and changes with the season.
  • An estimated 30,000 to 50,000 cases and 10,000 to 15,000 deaths occur each year, mostly among children. In endemic areas, the annual incidence of clinical disease ranges from 10 to 100 per 100,000 population. Children under 15 years of age are principally affected.
  • Most infections result in mild symptoms or no symptoms at all. 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 can be fatal in 30 percent of cases. About 20 percent of survivors will have serious cognitive and language impairment.
  • There is no specific treatment for JE. Care of patients focuses on treatment of symptoms and complications.
  • Vaccination is the single most important measure to control JE.

JE vaccine

  • The JE vaccine that has been most widely available internationally is an inactivated, mouse brain-derived vaccine. But it is labor intensive to produce, there is not enough available for everyone who needs it, and production of this vaccine has stopped in many places. Recent work has focused on developing and distributing newer vaccines that are easier and less expensive to produce, are more efficacious, have fewer side effects, and are easier to integrate into routine immunization schedules. This includes a vaccine that has been used for more than 20 years in China and has recently become available internationally. With the development and wider availability of improved vaccines, there are now better prospects for the control of JE in Asia.
  • Several other JE vaccines are in development, but there will be a longer timeline until they are widely available, particularly for children.
  • It is recommended that JE vaccination be extended to all endemic areas where the disease is considered a public health concern.

References