Japanese Encephalitis Vaccine
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Japanese Encephalitis Vaccine

En Español (Spanish Version)

What Is Japanese Encephalitis?

Japanese encephalitis is a mosquito-borne virus that leads to swelling of the brain. It can affect the central nervous system and cause severe complications, even death.

People get Japanese encephalitis when they are bitten by a mosquito infected with the virus.

Japanese encephalitis is the leading cause of viral encephalitis in Asia, with 30,000-50,000 cases reported each year. But less than one United States citizen per year traveling to or living in Asia is reported to have contracted Japanese encephalitis.

Symptoms include:

  • Fever
  • Chills
  • Tiredness
  • Headache
  • Neck stiffness
  • Nausea
  • Vomiting
  • Confusion
  • Agitation
  • Brain damage
  • Coma
  • Tremors
  • Convulsions (especially in infants)
  • Paralysis

Symptoms of Japanese encephalitis usually appear 5-15 days after the bite from an infected mosquito.

There is no specific treatment for Japanese encephalitis. Care for people with the disease is concentrated on treating specific symptoms and complications.

What Is the Japanese Encephalitis Vaccine?

The Japanese encephalitis vaccine is made from an inactive form of the virus. The vaccine is given by injection and should be stored between 35.6°F-46.4°F (2˚C-8˚C) prior to administration.

Who Should Get Vaccinated and When?

People who live or travel in certain rural parts of Asia, and laboratory workers who are at risk of exposure to the virus should receive the Japanese encephalitis vaccine.

The vaccine is given in three doses, with the second dose given seven days after the first, and the third dose given 30 days after the first. The third dose should be given at least 10 days before travel is planned. A booster dose may be required after two years.

Children aged 1-3 years get a smaller dose than older children and adults.

What Are the Risks Associated With the Japanese Encephalitis Vaccine?

Like any vaccine, the Japanese encephalitis vaccine is capable of causing problems such as severe allergic reactions, but the risk of serious harm or death is extremely small.

The most commonly reported problems associated with the Japanese encephalitis vaccine are mild and include:

  • Soreness, redness, or swelling near the injection site
  • Fever
  • Headache
  • Muscle pain
  • Abdominal pain
  • Rash
  • Chills
  • Nausea or vomiting
  • Dizziness

Rare problems include:

  • Seizure
  • Nervous system problems
  • Severe allergic reactions including:
    • Rash
    • Swelling of the hands and feet, face, or lips
    • Breathing difficulty

Who Should Not Get Vaccinated?

Children under one year of age do not normally get the vaccine.

People who have had a life-threatening reaction to mouse protein, thimerosal, or a previous dose of Japanese encephalitis vaccine should not get the vaccine.

People who have severe allergies (eg, history of hives or wheezing after a wasp sting or taking medications), women who are pregnant, nursing mothers, and people who will be traveling for fewer than 30 days (especially in major urban areas) should consult with their doctors before receiving the vaccine.

What Other Ways Can Japanese Encephalitis Be Prevented Besides Vaccination?

Since the Japanese encephalitis vaccine is not 100% effective at preventing the disease, it is important to protect yourself from mosquito bites. The US Centers for Disease Control and Prevention (CDC) recommends remaining in well-screened areas, wearing clothes that cover most of the body, and using an effective insect repellent (eg, those containing up to 30% N,N-diethyl metatoluamide, or "DEET") on skin and clothing to prevent mosquito bites.

What Happens in the Event of an Outbreak?

In the event of a Japanese encephalitis outbreak, people who are eligible for vaccination should receive it.


Immunization Action Coalition

Vaccine and Immunizations
Centers for Disease Control and Prevention


Directors of Health Promotion and Education website. Available at: http://www.dhpe.org/?Input=Japanese+encephalitis&image.x=20&image.y=14# . Accessed February 2, 2007.

UNICEF website. Available at: http://www.unicef.org/infobycountry/india_28555.html . Accessed February 2, 2007.

US Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/node.do/id/0900f3ec8000e2f3 . Accessed February 2, 2007.

US Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/vaccines/pubs/vis/downloads/vis-je.pdf. Accessed February 13, 2008.

Last reviewed February 2008 by David Horn, MD, FACP

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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