Japanese Encephalitis Vaccine and Immunodeficiency

• Generic Name: japanese enceph vacc sa14-14-2, inactivated
• Dosage Forms: n.a.
• Other Brand Names: Ixiaro

Prevention of disease caused by Japanese encephalitis virus in adults, adolescents, and children 2 months of age or older. Used to stimulate active immunity against Japanese encephalitis virus in travelers and other individuals (e.g., laboratory personnel) at risk of exposure to the virus.

Japanese encephalitis virus, a Flavivirus closely related to West Nile virus (WNV), St. Louis and Murray Valley encephalitis viruses, yellow fever virus, and dengue virus, is transmitted to humans through the bite of infected mosquitoes that acquired the virus by biting infected vertebrate hosts (usually pigs or wading birds). Humans are incidental or dead-end hosts for Japanese encephalitis virus since level or duration of viremia usually insufficient to infect mosquitoes. Direct person-to-person transmission of the virus does not occur; however, intrauterine transmission from mother to child during pregnancy can occur and transmission through blood products or transplanted organs theoretically could occur.

Endemic transmission of Japanese encephalitis virus reported in ≥24 countries in Southeast Asia and Western Pacific. Although infection with the virus usually results in asymptomatic or mild disease (fever, headache, aseptic meningitis), 1 out of every 200–250 infections results in severe disease (rapid onset of high fever, headache, vomiting, generalized weakness, neck stiffness, disorientation, seizures, spastic paralysis, coma, death). In areas where the virus is endemic, approximately 30,000–68,000 cases of Japanese encephalitis reported annually; case fatality rate is approximately 20–30% and 30–50% of survivors have permanent neurologic or psychiatric sequelae.

For most travelers to Asia, risk of acquiring Japanese encephalitis virus is very low, but varies depending on location and duration of travel, season, and traveler's expected activities. Overall incidence of Japanese encephalitis among individuals from nonendemic countries traveling in Asia is estimated to be <1 case per 1 million travelers. Although risk considered minimal for most short-term travelers (traveling for <1 month) who only visit urban areas in Asia, risk for travelers who stay for prolonged periods in rural areas where active transmission of Japanese encephalitis virus is occurring and short-term or recurrent travelers who have extensive outdoor or nighttime exposure in rural areas during periods of active transmission of the virus is probably similar to risk in susceptible resident populations.

Risk of transmission of Japanese encephalitis virus is greatest in rural agricultural areas where the virus is endemic and often is related to rice production and flooding irrigation, which results in large numbers of vector mosquitoes breeding in close proximity to amplifying vertebrate hosts. In temperate areas of Asia, Japanese encephalitis virus is transmitted seasonally (usually peaking in the summer and fall) and large seasonal epidemics can occur. In tropical and subtropical areas, transmission of the virus can be sporadic or occur all year, but often peaks during the rainy season.

When making recommendations regarding vaccination against Japanese encephalitis virus for travelers, consider overall low risk for travel-associated Japanese encephalitis virus disease, high morbidity and mortality associated with Japanese encephalitis, low probability of serious adverse effects following vaccination, and vaccine cost. Also consider planned itinerary, including destinations, duration of travel, season, accommodations, and activities as well as possibility of unexpected travel to high-risk areas.

Travelers planning to spend ≥1 month in endemic areas during Japanese encephalitis virus transmission season: USPHS Advisory Committee on Immunization Practices (ACIP) and CDC recommend vaccination with JE-VC for all such travelers. This includes long-term travelers, recurrent travelers, or expatriates who will be based in urban areas but are likely to visit endemic rural or agricultural areas during a high-risk period of Japanese encephalitis virus transmission.

Short-term travelers (traveling for <1 month) to endemic areas during Japanese encephalitis virus transmission season if they are planning to travel outside of urban areas or do activities associated with increased exposure: ACIP and CDC state that vaccination with JE-VC should be considered for such travelers. This includes those who will spend substantial time outdoors in rural or agricultural areas (especially during the evening or nighttime), those who will participate in extensive outdoor activities (e.g., camping, hiking, trekking, biking, fishing, hunting, farming), and those staying in accommodations without air conditioning, screens, or bed nets.

Travelers to areas with an ongoing Japanese encephalitis outbreak and travelers to endemic areas who are uncertain of specific destinations, activities, or duration of travel: ACIP and CDC state that vaccination with JE-VC should be considered for such travelers.

Short-term travelers (traveling for <1 month) to Asia when visit restricted to urban areas or times outside a well-defined Japanese encephalitis virus transmission season: Vaccination with JE-VC not recommended.

All individuals considering travel to areas where Japanese encephalitis has been reported: Because risk of infection with Japanese encephalitis virus is highly variable within endemic regions and varies from year to year within a given region, consult current CDC recommendations for international travel for information concerning geographic areas where transmission of the virus is being reported. Information on risk of Japanese encephalitis in specific countries, information on mosquito avoidance and protective measures against mosquito bites, and additional information regarding benefits and risks of JE-VC vaccination in travelers is available from CDC.

Laboratory personnel at risk of exposure to infectious Japanese encephalitis virus: ACIP recommends vaccination with JE-VC for all such workers. Laboratory-acquired cases of Japanese encephalitis reported; the virus may be transmitted in laboratory settings through needlestick injuries or, theoretically, through mucosal or inhalational exposures.