Disease Description: Japanese encephalitis virus (JEV) is a mosquito-borne Flavivirus that is closely related to West Nile and St. Louis encephalitis viruses. The majority of human infections with JEV are asymptomatic, and only about 1 in 250 infected persons develops clinical disease. Encephalitis is the most common clinical manifestation of JEV infection. From 35,000 to 50,000 cases of JE are reported to WHO each year, resulting in an estimated 10,000 to 15,000 deaths annually.
Risk to Travelers: JEV infection occurs throughout most of Asia and is the most common cause of encephalitis in that region (Map). Risk varies by season and location. The risk to short-term travelers and those who confine their travel to urban centers is very low. Expatriates and travelers living for prolonged periods in rural areas where JE is endemic or epidemic are at greater risk.
Prevention - Vaccine: Vaccination should be considered for persons who plan to live in areas where JE is endemic or epidemic and for travelers whose activities include trips into rural farming areas. Short-term travelers, especially those whose visits are restricted to major urban areas, are at lower risk for infection and generally do not require the vaccine. An inactivated mouse brain-derived JE vaccine (JE-VAX) has been licensed for use in the U.S. civilian population since 1992 but is no longer available. A new inactivated cell culture-derived JE vaccine (IXIARO) has been approved by the FDA and is available for administration to persons 17 years and older. Two shots of IXIARO are required, 28 days apart.
Vaccine Adverse Effects: Pain and tenderness were the most commonly reported symptoms in a safety study with 1,993 participants who received 2 doses of Ixiaro. Systemic side effects, including headache, myalgia, fatigue, and an influenza-like illness, were each reported at a rate of >10%. Because Ixiaro was licensed after study in <5,000 recipients, the possibility of rare serious adverse events cannot be excluded. Postlicensure studies and surveillance are further evaluating the safety of Ixiaro in a larger population.
Vaccine Contraindications: A history of allergy or hypersensitivity reaction to a previous dose of JE-VAX or IXIARO (or components of the vaccines) is a contraindication to receiving additional doses.
Vaccine Booster Recommendations: If the primary series of Ixiaro was administered ≥1 year previously, a booster dose should be given prior to potential reexposure or if there is a continued risk for JEV infection.
Information adapted from CDC Health Information for International Travel (the Yellow Book), http://www.cdc.gov/travel/yellowbook/2010/table-of-contents.htm