More about Japanese encephalitis (JE)

This page provides links to PATH's work on Japanese encephalitis (JE) and information about the disease and related vaccines.

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 the southeastern Russian Federation. 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 is fatal in 30 percent of cases. About 30 percent of survivors will have serious cognitive and language impairment.
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.

The JE vaccine that has been most widely available internationally is an inactivated, mouse brain-derived vaccine. However, there are several constraints to this vaccine: 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. These include the SA 14-14-2 JE vaccine—a live, attenuated vaccine that has been used for more than 20 years in China and has recently become available internationally. Several other JE vaccines are in development, but studies of their safety and efficacy among children are currently ongoing.
The World Health Organization (WHO) recommends that JE vaccination be extended to all endemic areas where the disease is considered a public health concern.

Page last updated: August 2008.