A Look at Each Vaccine: Japanese Encephalitis Virus Vaccine
Shortage: The Japanese encephalitis virus vaccine is expected to be in short supply for children until at least 2010.
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 only for people who travel to the Far East and engage in certain high-risk activities. The JEV vaccine is given as a series of three shots and can be administered to anyone over 1 year of age: the second shot is given seven days after the first, and the third is given 30 days after the first.
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 World Health Organization Web site 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 JEV vaccine is made by taking the virus and growing it in the brains of mice. The virus is then purified, and treated with the chemical formaldehyde. Because the virus is inactivated or killed, it cannot possibly cause JEV. The vaccine is highly effective at preventing JEV.
The JEV vaccine is given as a series of three shots. The second shot is given seven days after the first, and the third shot is given 30 days after the first. The best protection is afforded about 10 days after the series is completed — so you should make sure that, if you are planning on getting the JEV vaccine, you give yourself plenty of time.
Does the JEV vaccine have side effects?
The JEV vaccine has a fairly high rate of mild side effects. Mild side effects include fever, headaches, muscle aches and malaise, and occur in about one in every five people who receive the vaccine.
Who should get the JEV vaccine?
Fortunately, if you intend to stay in cities or stay for less than a 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
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Planning activities such as biking, camping or other outdoor activities with prolonged periods of exposure to mosquitoes
How can you avoid JEV?
As for 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:
- Use mosquito netting over the bed.
- Wear long-sleeved shirts and long pants.
- Wear insect-repellants with DEET on exposed skin.
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Wear clothing treated with insect-repellants such as permethrin.
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. Further, the JEV vaccine has a high rate of side effects. The vaccine causes severe allergic reactions in as many as one in 200 recipients of the vaccine. 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.
Reviewed by: Paul A. Offit, MD
Date: March 2008
Materials in this section are updated as new information becomes available. Center staff regularly review 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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