A Look at Each Vaccine: Japanese Encephalitis Virus (JEV) Vaccine

The mosquito-borne virus, Japanese encephalitis virus (JEV), does not just occur in Japan. JEV also occurs in many regions of the Far East. However, the United States does not recommend the JEV vaccine for everyone traveling to the Far East. Rather, the vaccine is recommended based on aspects of travel such as location, length of stay and planned activities.

  • The disease

    What is Japanese encephalitis virus?

    Japanese encephalitis virus (JEV) is a virus that causes encephalitis (inflammation of the brain) and, like yellow fever virus, is transmitted by the bite of a mosquito. Symptoms begin about one to two weeks after the bite. Afflicted individuals usually have fever, headache, stiff neck, nausea and vomiting. About one of every four people infected with the virus will develop coma and die. Of those who survive, about half will have permanent brain damage. JEV is the most common cause of encephalitis in the world.

    Where do you catch JEV?

    JEV infections occur in many areas throughout the world. Visit the Centers for Disease Control and Prevention (CDC) travel website for current information regarding the risk of getting JEV while traveling.

    How do you catch JEV?

    JEV is transmitted by the bite of a mosquito. Fortunately, the risk of catching JEV is very low. In a 14-year period, between 1978 and 1992, only 11 people traveling from the United States to the Far East caught JEV. Most of those infected were members of the U.S. military who were in the field.

    How can you avoid JEV?

    As with yellow fever, the best way to avoid JEV is to avoid being bitten by a mosquito. Between dusk and dawn, when mosquitoes most often appear to feed, you and your child should take refuge indoors and remember to:

    • Use mosquito netting over the bed
    • Wear long-sleeved shirts and long pants
    • Wear insect-repellants with DEET on exposed skin
    • Wear clothing treated with insect-repellants such as permethrin
    • Stay in accommodations with air conditioning or screens
  • The vaccine

    How is the JEV vaccine made?

    The only JEV vaccine currently available in the United States is licensed for use in people 17 years of age and older. Known as IXIARO® and licensed in 2009, this version is made by growing the virus in cells in the laboratory and then purifying it and killing it with a chemical. Like the previous JEV vaccine, it cannot possibly cause JEV because the virus is killed. IXIARO® is given in two doses with the second given 28 days after the first. Because it takes about one month to complete the series, and about another week to develop protective antibodies, you should plan ahead to be sure you have enough time to be protected before your trip. Decisions regarding use of this vaccine prior to travel are complex; therefore, travelers should seek more information by visiting the CDC’s travel website as well as by visiting a travel clinic to determine whether or not vaccine is needed.

    Althrough the JEV vaccine is not licensed for use in children between 1 and 16 years of age, the CDC allows its use in children 2 months to 16 years of age who would benefit from the vaccine prior to traveling. The CDC made this recommendation in 2013 after studies showed that the vaccine was safe and immunogenic. However, children younger than 2 years of age only get half of the regular dose. Find out more about JE vaccine and children on the CDC’s website.

    Does the JEV vaccine have side effects?

    The JEV vaccine may cause mild side effects in a small number of recipients, including headaches, muscle aches and malaise, and occur in about 1 of every 5 people who receive the JEV vaccine. Redness, swelling or a lump at the injection site occurs in about one in 100 vaccine recipients.

    Who should get the JEV vaccine?

    Fortunately, if you intend to stay in cities or stay for less than one month, the risk of catching JEV is very low. However, the JEV vaccine is recommended for those traveling to high-risk areas who are:

    • Staying in rural or farm areas
    • Staying for more than 30 days
    • Planning activities such as biking, camping, or other outdoor activities with prolonged periods of exposure to mosquitoes
    • Staying in accommodations without air conditioning, screens or bed nets
    • Traveling to an area with an ongoing outbreak
    • Traveling to an area known to have risk, but without specific information about destinations, activities or duration of travel
  • Other questions you might have

    What should we do if our newly adopted daughter started the  Japanese Encephalitis (JE) vaccine while in China but did not complete the series before we brought her to the U.S.?

    In the U.S., the Japanese Encephalitis (JE) vaccine is only recommended for people who are likely to be exposed to JE during travel. If your daughter will be making a trip back to China or to somewhere else that would increase her risk, then she would need to get the second dose. However, you should consult a travel clinic as the determination of need is based on trip-specific information, such as exactly where she is going, how long she will be there and what she will be doing.

  • Relative risks and benefits

    Do the benefits of the JEV vaccine outweigh its risks?

    JEV is a devastating illness that frequently causes permanent brain damage or death in those infected. Fortunately, JEV is an uncommon cause of disease in those traveling from the United States to regions of the Far East where the disease is prevalent. No more than about one case per year occurs in travelers. And when the disease does occur in travelers, it occurs only in those who have stayed for longer than 30 days, extensively camped or biked, or have stayed in rural areas. Therefore, the benefits of the JEV vaccine only outweigh its risks for those who are traveling to the Far East and who plan on staying for a long time and engaging in high-risk activities.

    Disease risks

    • Fever, headache, stiff neck, nausea and vomiting
    • Encephalitis (inflammation of the brain)
    • Coma and death (1 of every 4)
    • Permanent brain damage (1 of every 2 survivors)

    Vaccine risks

    • Headaches, muscle aches, and malaise (1 in 5 people)
    • Redness, swelling or lump at injection site (1 in 100 people)
  • Reference

    Plotkin SA, Orenstein W, and Offit PA. Japanese encephalitis vaccines in Vaccines, 6th Edition. 2012, 312-351

Reviewed by Paul A. Offit, MD on August 25, 2014

Materials in this section are updated as new information and vaccines become available. The Vaccine Education Center staff regularly reviews materials for accuracy.

You should not consider the information in this site to be specific, professional medical advice for your personal health or for your family's personal health. You should not use it to replace any relationship with a physician or other qualified healthcare professional. For medical concerns, including decisions about vaccinations, medications and other treatments, you should always consult your physician or, in serious cases, seek immediate assistance from emergency personnel.