Health Features

Frequently Asked Questions: JAPANESE ENCEPHALITIS

What is Japanese Encephalitis (JE)?

It is a potentially severe disease caused by a virus spread by infected mosquitoes in Asia and the western Pacific. The Japanese Encephalitis virus is one of a group of mosquito-transmitted viruses that can cause inflammation of the brain. 

How is JE transmitted?

It is caused by the JE virus and is transmitted by the mosquito Culex tritoeniorhynchus which breeds in water pools and flooded rice fields. The mosquito becomes infected with the Japanese Encephalitis virus when feeding on domestic pigs and wild birds infected with the virus. A mosquito vector which has taken a blood meal from an infected animal host can bite humans, who then may develop infection or actual disease.

How soon do people get sick after being bitten by an infected mosquito?

It takes 5 to 15 days after the bite of an infected mosquito to develop symptoms.

What are the signs and symptoms OF JE?

Most people who are infected develop mild symptoms or no symptoms at all. In those who develop severe disease, initial symptoms include fever, chills, headache, nausea, vomiting and fatigue. About 1 in 250 infections can progress to inflammation of the brain (encephalitis) which can be accompanied by seizures, confusion and disorientation. Coma and paralysis occur in some cases. It can occur at all ages.

Is JE a serious illness?

The disease is fatal in 20% - 50% of persons with encephalitis.

Can the mosquitoes transmit the virus from an infected person to another person?

As the virus does not multiply in the human host, it cannot be transmitted by mosquito from man to man.

Can a person get infected through close contact with an infected person?

No. The virus has not been shown to be transmitted from man to man.

Who is at risk of getting the infection?

Persons living in rural area in endemic locations are most at risk. In tropical countries like the Philippines, transmission can occur year-round but often intensifies during the rainy season and pre-harvest period in rice-cultivating regions.

How is Japanese encephalitis diagnosed?

Diagnosis is based on a combination of clinical signs and symptoms and specialized laboratory tests of blood or spinal fluid. These tests typically detect antibodies that the immune system makes against the viral infection.

What is the treatment for JE?

There is no specific treatment for JE. Intensive supportive therapy is indicated. This may include hospitalization, respiratory support and intravenous fluids.

How can people reduce the chance of getting infected?

Use insect repellent and wear long pants and sleeves. Sleep in air-conditioned or well-screened rooms or use bed nets. A vaccine against JE virus is also available. Talk to your healthcare provider about whether this vaccine is right for you.

Is vaccination available?

Yes. JEV is the most common vaccine-preventable cause of encephalitis in Asia and vaccination is the most effective strategy to prevent and control JE. In the Philippines, the only vaccine available and approved by the FDA against JE is the Japanese Encephalitis live attenuated recombinant, chimeric vaccine (JE-CV). It is given through the subcutaneous route to children 9 months and above, including adults.

How effective is the vaccination?

Randomized studies have shown that live attenuated JE-CV vaccination can provide protection above 90% as early as 14 days post-vaccination, and 84% protection five years after injection with a single dose. The vaccine was also studied to confer to most adults a high level of protection for at least 10 years.

Who should be considered for vaccination against JE?

JE-CV is recommended for individuals aged 9 months and older, to be given subcutaneously as a single dose.

For travelers going to areas endemic with JE such as Bangladesh, Bhutan, Brunei, Burma, Cambodia, China, India, Indonesia, Japan, Korea, Laos, Malaysia, Nepal, Papua New Guinea, Singapore, Taiwan, Thailand, Timor Leste and Vietnam.

The vaccine is recommended in the following schedule and dose:

  • Children 9mos up to 17yrs, as a single primary dose, followed by a booster dose at 12-24mos after the primary dose.
  • For immunocompetent adults, as single primary dose, with no booster dose needed.

For those who wish to be protected, vaccine can be given at any time if without contraindications.

Are there any side effects of the vaccination?

There are no serious side effects. The vaccine has an acceptable safety profile and tolerability. Local and mild side effects such as tenderness, redness and swelling at the site of injection are commonly reported symptoms. Fever, headache, malaise, rash, muscle pain and dizziness may occur in up to 10% of vaccinated persons.

How can Centre Medicale Internationale help you avoid JE?

At CMI, you may consult our primary care physicians, pediatricians and internal medicine speciallists for further advice. Japanese Encephalitis live attenuated recombinant, chimeric vaccine (JE-CV) is available for administration in CMI.


  1. Japanese Encephalitis Vaccines: WHO Position paper, February 2015. Weekly Epidemiol Rec 2015; 90(9):69-88.
  2. Department of Health, Epidemiology Bureau Weekly Surveillance Report. Retrieved from http://www.doh.gov.ph/statistics
  3. Torresi et al. Immunogenicity, safety and tolerability in adults of a new single-dose, live-attenuated vaccine against Japanese encephalitis; randomized controlled phase 3 trials. Vaccine.2010; 28: 7993-8000.
  4. Desai K et al. Modelling the long-term persistence of neutralizing antibody in adults after one dose of live attenuated Japanese encephalitis chimeric virus vaccine. Vaccine. 2012;30: 2510-2515.
  5. Japanese Encephalitis. Retrieved from http://www.cdc.gov/japaneseencephalitis
  6. Japanese Encephalitis. Fact Sheet No 386. December 2015. Retrieved from http://www.who.int/mediacentre/factsheets/fs386/en/
  7. Position Paper on Japanese Encephalitis Vaccines. Pediatric Infectious Diseases Society of the Philippines, a specialty society of the Philippine Pediatric Society. 2017.