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Japanese Encephalitis Vaccine

What Is Japanese Encephalitis?

Japanese encephalitis is a virus that is spread by mosquitoes. It can cause swelling of the brain. It also affects the central nervous system. Japanese encephalitis can cause severe complications, like long-term neurological disability and death.

People get Japanese encephalitis when they are bitten by a mosquito infected with the virus. Japanese encephalitis is a common cause of viral encephalitis in Asia. It can be prevented with a vaccine.

Many people with the infection may have no symptoms. If symptoms develop, they can include:

  • Fever
  • Chills
  • Tiredness
  • Headache
  • Neck stiffness
  • Nausea
  • Vomiting
  • Confusion
  • Restlessness
  • Brain damage
  • Coma
  • Tremors
  • Convulsions, especially in infants

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

There is no specific treatment for this condition. Care for people with the disease is aimed at easing symptoms.

What Is the Japanese Encephalitis Vaccine?    TOP

The vaccine is made from an inactive form of the virus. It is called Ixiaro and is for people aged 17 years and older.

IMOJEV is a vaccine made from live virus that is weakened. It is not available in the United States.

Who Should Get Vaccinated and When?    TOP

The vaccine is recommended for people who are traveling to Asia and are:

  • Planning to stay at least a month where there have been Japanese encephalitis
  • Planning on staying less than a month, but will be in rural areas or outdoors a lot
  • Going to an area of Japanese encephalitis outbreaks
  • Unsure where they will be staying

Lab workers who may be exposed to Japanese encephalitis should also get the vaccine.

There is no vaccine available in the United States for young children. Children under age 17 who will be traveling to a high-risk area can visit a travel clinic abroad or enroll in a clinical trial. Visit the Centers for Disease Control and Prevention (CDC) website for more information.

The Japanese encephalitis vaccine is given in a series of 2 shots within 28 days. The last dose needs to be given within 1 week of traveling to Asia.

What Are the Risks Associated With the Japanese Encephalitis Vaccine?    TOP

Like any vaccine, the Japanese encephalitis vaccine can cause problems, such as severe allergic reactions. The risk of serious harm or death is extremely small.

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

  • Soreness, redness, or swelling near the injection site
  • Headache
  • Muscle pain

Who Should Not Get Vaccinated?    TOP

Talk to your doctor before getting the vaccine if you:

  • Have ever had a life-threatening reaction to this vaccine
  • Have severe allergic reactions
  • Are pregnant
  • Will be traveling to an urban area for less than 30 days

What Other Ways Can Japanese Encephalitis Be Prevented Besides Vaccination?    TOP

The vaccine is not 100% effective at preventing the disease. It is important to protect yourself from mosquito bites. The CDC recommends:

  • Staying in well-screened areas
  • Wearing clothes that cover most of the body
  • Using an effective insect repellent (such as those containing up to 30% N,N-diethyl-meta-toluamide, [DEET]) on skin and clothing to prevent mosquito bites

What Happens in the Event of an Outbreak?    TOP

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

Vaccines & Immunizations
Centers for Disease Control and Prevention
Immunization Action Coalition


Clinical trials sites in the United States for Ixiaro in children under 17. Centers for Disease Control and Prevention website. Available at
...(Click grey area to select URL)
Accessed November 19, 2013.
Dubischar-Kastner K, Kaltenboeck A, Klingler A, Jilma B, Schuller E. Safety analysis of a Vero cell culture-derived Japanese encephalitis vaccine, IXIARO (IC51), in 6 months of follow-up. Vaccine. 2010;28(39):6463-6469.
Fischer M, Lindsey N, Staples JE, Hills S, Centers for Disease Control and Prevention (CDC). Japanese encephalitis vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2010;59(RR-1):1-27.
Halstead SB, Thomas SJ. New Japanese encephalitis vaccines: alternatives to production in mouse brain. Expert Rev Vaccines. 2011;10(3):355-364.
Halstead SB, Thomas SJ. Japanese encephalitis: new options for active immunization. Clin Infect Dis. 2010;50(8):1155-1164.
Lehtinen VA, Huhtamo E, Siikamaki H, Vapalahti O. Japanese encephalitis in a Finnish traveler on a two-week holiday in Thailand. J Clin Virol. 2008;43(1):93-95.
Wilder-Smith A, Halstead SB. Japanese encephalitis: update on vaccines and vaccine recommendations. Curr Opin Infect Dis. 2010;23(5):426-431.
Last reviewed November 2015 by David L. Horn, MD
Last Updated: 12/20/2014

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