Japanese Encephalitis

Japanese encephalitis (JE) is a viral infection caused by the Japanese encephalitis virus (JEV). It is primarily transmitted through the bite of infected mosquitoes, particularly Culex mosquitoes, which breed in rice paddies and waterlogged areas. The disease is most commonly found in rural and agricultural areas of Asia, including countries such as Japan, China, Korea and parts of Southeast Asia.


Most individuals infected with Japanese encephalitis virus do not develop symptoms. However, for those who do, the symptoms can range from mild flu-like symptoms to severe neurological complications. Signs and symptoms may include fever, headache, vomiting, neck stiffness, seizures, confusion and even coma.


Japanese encephalitis is primarily transmitted through the bite of infected mosquitoes. Pigs and birds serve as reservoir hosts for the virus and mosquitoes become infected by feeding on infected animals. Humans are considered incidental hosts and do not contribute significantly to the transmission cycle.

Risk factors

People who live in or travel to areas where Japanese encephalitis is endemic are at a higher risk of infection. The risk is highest in rural agricultural areas, especially during the peak transmission season, which varies depending on the region.


Vaccination is an effective preventive measure against Japanese encephalitis. The vaccine is recommended for individuals travelling to endemic areas or residing in areas with ongoing transmission. Additionally, personal protective measures, such as using mosquito repellents, wearing long-sleeved clothing, and staying in air-conditioned or screened accommodations, can help reduce the risk of mosquito bites.


There is no specific antiviral treatment for Japanese encephalitis. Supportive care is provided to manage symptoms and complications. In severe cases, hospitalisation may be required and patients may need intensive care to manage neurological symptoms.

Long-term effects

Survivors of Japanese encephalitis may experience long-term neurological complications, including paralysis, movement disorders, cognitive deficits and behavioural changes. These complications can have a significant impact on the quality of life.

Types of vaccines

The Japanese encephalitis (JE) vaccine is a preventive measure against Japanese encephalitis virus (JEV) infection. The vaccine helps to reduce the risk of developing the disease, especially for individuals travelling to or residing in areas where JE is endemic or experiencing outbreaks.

The most commonly used vaccines include inactivated vaccines, such as the Vero cell-derived inactivated JE vaccine and the mouse brain-derived inactivated JE vaccine. These vaccines contain inactivated forms of the virus and are administered via intramuscular injection.

Vaccination schedule

The vaccination schedule for Japanese encephalitis can vary depending on the vaccine brand and the individual’s age and previous immunisation history. In general, the primary vaccination schedule consists of two doses given a few weeks apart. A booster dose may be recommended for long-term protection, usually administered one year after the primary series.

Timing of vaccination

It is advisable to complete the full vaccine series before potential exposure to Japanese encephalitis virus. This is particularly important for individuals planning to travel to or reside in endemic areas. Starting the vaccination series several weeks before travel allows sufficient time for the immune response to develop.

Targeted population

The JE vaccine is primarily recommended for travellers to endemic areas or individuals residing in such regions. It is often suggested for long-term travellers, expatriates and military personnel stationed in areas with JE transmission. The vaccine is not routinely recommended for individuals who are not at risk of exposure to the virus.

Vaccine efficacy and side effects

The Japanese encephalitis vaccine is generally safe and effective. The inactivated vaccines have been shown to provide good protection against the disease. Like any vaccine, mild side effects such as pain at the injection site, redness or swelling can occur. Serious side effects are rare.

If you are planning to travel to an area where Japanese encephalitis is prevalent, it is recommended to consult with a healthcare professional or a travel medicine specialist. They can assess your specific risk factors, provide guidance on vaccination and address any concerns or questions you may have.

Remember that while the JE vaccine is an important preventive measure, it does not replace other protective measures, such as avoiding mosquito bites by using repellents, wearing protective clothing and staying in screened accommodations.