Questions & Answers
Japanese encephalitis
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The Disease

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  1. What is Japanese encephalitis (JE)?

    It is a severe infection of the brain and spinal cord caused by the bite of a Culex mosquito carrying the JE virus.  The disease is most common in rural, agricultural areas of Asia and parts of the western Pacific where mosquito larvae inhabit flooded rice fields and marshes.  These mosquitoes feed outdoors from dusk until dawn.  Disease transmission occurs when mosquitos are active, usually during summer and fall.

    JE is only transmitted by mosquitos – never from person-to-person.  It is the most common vaccine-preventable cause of encephalitis in Asia with 30,000 to 50,000 cases reported annually.

  2. Who is at risk for getting JE?

    JE occurs in Asia and parts of the Western Pacific. The risk of infection is highest in rural agricultural areas where rice production and flooding irrigation take place, and large numbers of mosquitoes breed in proximity to pigs and wading birds.  Individuals are at an increased risk of JE if they spend lots of time outdoors, especially during the evening;  when mosquitos are biting; participate in extensive outdoor activities (e.g., camping, hiking, trekking, biking, fishing, hunting or farming); or stay in accommodations without air conditioning, screens, or bed nets.
    In most temperate areas of Asia, JE transmission is seasonal, and substantial epidemics can occur, usually peaking in summer and fall.  In the subtropics and tropics, transmission can occur year-round, often intensifying during the rainy season.  JE can be prevented with a vaccine, but risk can also be reduced by the use of countermeasures, such as insect repellent, permethrin-treated clothing, and vector avoidance.

    Visit the CDC JE webpage to see a geographic distribution of the JE virus.

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  1. What are the symptoms of JE?

    Most infections cause no symptoms. Mild infections cause a fever with headache.  Severe infection is rare, but develops rapidly, and causes intense headache, high fever, neck stiffness, disorientation, tremors, seizures (especially in infants), spastic paralysis, and coma.  Severe disease is deadly in 25% of infections.

  2. How is JE treated?

    Therapy for symptomatic JE infection is supportive.  Patients often require tube feeding, airway management, and anticonvulsants for seizure control.  No clearly effective antiviral agents exist.

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  1. What are some specific complications of JE?

    About half of the people who survive serious JE infection are left with neurologic and psychological sequelae including intellectual disabilities, paralysis, and seizures.

The Vaccine

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  1. Is there a vaccine to prevent JE?

    Yes.  IXIARO®, manufactured in the United Kingdom by Intercell Biomedical, has been licensed in the U.S. since March 2009.  IXIARO® is used for immunization against JE in persons 2 months of age and older.

  2. Who should be immunized against JE?

    Individuals deploying to areas in PACOM should be administered the JE vaccine in accordance with the latest PACOM Force Health Protection guidance. Laboratory workers with potential exposure to infectious JE virus should also be vaccinated.

    JE vaccination is highly recommended for Service members, DOD civilians, and beneficiaries who are stationed or who visit for more than 30 days in endemic areas.  This includes those who would be based in urban areas, but likely to visit endemic rural or agricultural areas during a high-risk period of JE transmission.

    JE vaccination is also recommended for Service members and beneficiaries traveling outside urban areas or who have an increased risk of exposure due to extensive outdoor activities; to an area with an ongoing JE outbreak; to endemic areas or who are uncertain about specific destinations, activities, or duration of travel.

    Visit the CDC JE webpage to see a geographic distribution of the JE virus.

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  1. How is JE vaccine administered?

    IXIARO® is an inactivated virus vaccine injected intramuscularly in a two-dose series.  Doses are administered on day zero (the day of initial immunization) and on day twenty-eight.  The IXIARO® series should be completed at least one week prior to potential exposure to JEV.  IXIARO® only comes in 0.5 mL pre-filled syringes.

    1. For children 2 – 35 months of age, a single dose is 0.25 mL and for individuals 3 years of age and older, a single dose is 0.5 mL.
    2. To administer a 0.25 mL dose, expel and discard half of the volume from the 0.5 mL pre-filled syringe by pushing the plunger stopper up to the edge of the red line on the syringe barrel prior to injection.

    A one-time booster dose is recommended for persons 17 years and older if more than one year has passed since completing the primary series and the risk of exposure to the JE virus continues.  Timing of additional booster doses has not yet been determined.  IXIARO® cannot be used as a booster dose for previously administered JE-Vax®.  Previous doses of JE-Vax® are considered void, and the two dose series of IXIARO® should be administered for continued protection against JE.

  2. What are the most common side effects following JE immunizations?

    The most common side effects for children 2 months to one year are injection site redness, fever, irritability, and diarrhea.  The most common side effects for individuals 1 year and older are injection site pain or tenderness, fever, headache, and myalgia. Contact your health care provider if you have any of the following problems because these may be signs of an allergic reaction:

    • difficulty breathing
    • hoarseness or wheezing
    • hives
    • dizziness, weakness or fast heart beat

  3. Are there special restrictions for personnel on flying status?
    Temporary flying restrictions are per Service specific policy.

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  1. Who should not receive the JE vaccines?

    People who had a severe allergic reaction to a previous dose of IXIARO® or other JE vaccine, or are allergic to any component of IXIARO®, including protamine sulfate, should not be vaccinated.  IXIARO® contains protamine sulfate, known to cause hypersensitivity reactions in some individuals.

    Safety and effectiveness of IXIARO® has not yet been established in pregnant women or nursing mothers.  Pregnant women should generally not receive JE vaccine.  Check with your doctor since it could be recommended under certain circumstances.

    If you will be traveling for fewer than 30 days, especially if you will be staying in major urban areas, tell your doctor.  You may be at a lower risk and not need the vaccine.

  2. What should I tell my health care professional before I am vaccinated with IXIARO®?

    It is very important to tell your health care provider if you:

    • have had an allergic reaction to a previous dose of IXIARO or any other JE vaccine;
    • have a bleeding disorder or a reduction in blood platelets, which increases risk of bleeding or bruising (thrombocytopenia) and cannot receive injections in the arm;
    • have a weakened immune system, for example, due to a genetic defect or HIV infection;
    • are or may be pregnant, or are breast feeding - IXIARO has not been studied in pregnant women or nursing mothers;
    • currently have any illness with a fever of more than 100°F (37.8°C);
    • take any medicines, even those you can buy over the counter.

Adapted from the Immunization Action Coalition (with permission)
and the Centers for Disease Control and Prevention (CDC).