Vaccine Education Center

A Look at Each Vaccine: Japanese Encephalitis Virus 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.

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, neck stiffness, 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.

Where do you catch JEV?

JEV infections occur in many areas throughout the world. Visit the Centers for Disease Control and Prevention 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 is the JEV vaccine made?

The only JEV vaccine currently available in the United States is 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.

Currently, there is no JEV vaccine licensed for use in children between 1 and 16 years of age; however, studies regarding the safety and immunogenicity of IXIARO in children less than 17 years old are currently being completed. Information regarding JEV vaccine options for children less than 17 years of age is available from the Centers for Disease Control and Prevention.

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 one in every five 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:

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. Also, remember to:

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.

Some travelers
Disease Risks Vaccine Risks
  • One to two weeks after a mosquito bite: fever, headache, neck stiffness, nausea and vomiting
  • Encephalitis (inflammation of the brain)
  • Coma and death (1 of every 4)
  • Permanent brain damage (1 of every 2 survivors)
  • Headaches, muscle aches, and malaise (1 in 5 people)
  • Redness, swelling or lump at injection site (1 in 100 people)


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

Reviewed by: Paul A. Offit, MD
Date: April 2013

Materials in this section are updated as new information becomes 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.


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