What Is 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:
- Neck stiffness
- Nausea or vomiting
Convulsions, especially in infants
- Brain damage
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?
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?
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.
The vaccine is made from an inactive form of the virus. The IXIARO vaccine is approved for use starting at age 2 months and is the only one available in the US.
IMOJEV is another vaccine made from live virus that is weakened. It is not available in the US.
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?
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
- Muscle pain
Who Should Not Get Vaccinated?
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?
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% 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.
WHERE CAN I GET MORE INFORMATION?
Immunization schedules. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/vaccines/schedules/index.html. Updated February 6, 2017. Accessed December 7, 2017.
Japanese encephalitis. Centers for Disease Control and Prevention website. Available at:
Accessed August 5, 2015. Accessed December 7, 2017.
Japanese encephalitis VIS. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/vaccines/hcp/vis/vis-statements/je-ixiaro.html. Updated January 24, 2014. Accessed December 7, 2017.
Mosquito avoidance. EBSCO DynaMed Plus website. Available at:
http://www.dynamed.com/topics/dmp~AN~T115142/Mosquito-avoidance. Updated November 21, 2016. Accessed December 7, 2017.
Vaccine is key to preventing outbreaks of Japanese encephalitis. UNICEF website. Available at:
December 7, 2017.
Last reviewed December 2017 by EBSCO Medical Review Board
David L. 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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