Japanese Encephalitis Vaccines

Introduction to Japanese Encephalitis Vaccines

Japanese encephalitis (JE) is a mosquito-borne flavivirus infection that can cause severe neurological disease. Vaccination is the most effective preventive measure against JE. This section provides an overview of JE vaccines and their importance in public health.

Key Points:

  • JE is endemic in many parts of Asia and the Western Pacific
  • The disease has a high mortality rate (20-30%) and neurological sequelae in survivors
  • Vaccines have been available since the 1930s and have significantly reduced JE incidence
  • Modern JE vaccines are safe, effective, and recommended for travelers and residents in endemic areas

Types of Japanese Encephalitis Vaccines

Several types of JE vaccines have been developed over the years. This section details the various vaccine types, their composition, and their availability.

1. Inactivated Mouse Brain-derived Vaccine

  • Derived from infected mouse brain tissue
  • No longer recommended due to safety concerns and availability of newer vaccines
  • Example: JE-VAX (no longer produced)

2. Inactivated Vero Cell Culture Vaccines

  • Produced using Vero cells infected with JE virus
  • Examples: IXIARO/JESPECT, JEEV
  • IXIARO is licensed in many countries for use in adults and children

3. Live Attenuated Vaccines

  • Contain weakened JE virus strains
  • Example: SA14-14-2 vaccine (widely used in China and other Asian countries)
  • Single dose provides long-lasting immunity

4. Chimeric Vaccines

  • Recombinant vaccines using yellow fever vaccine virus as a vector
  • Example: IMOJEV (licensed in Australia and some Asian countries)
  • Single dose induces rapid and long-lasting immunity

Vaccine Administration

Proper administration of JE vaccines is crucial for their effectiveness. This section covers dosing schedules, routes of administration, and considerations for different populations.

IXIARO/JESPECT (Inactivated Vero Cell Vaccine)

  • Primary series: 2 doses, 28 days apart
  • Adults: 0.5 mL per dose
  • Children (2 months to <3 years): 0.25 mL per dose
  • Route: Intramuscular injection
  • Booster: 12-24 months after primary series if ongoing exposure or re-exposure is expected

SA14-14-2 (Live Attenuated Vaccine)

  • Single 0.5 mL dose
  • Route: Subcutaneous injection
  • Used in children in endemic countries; not widely available internationally

IMOJEV (Chimeric Vaccine)

  • Single 0.5 mL dose
  • Route: Subcutaneous injection
  • Approved for use in individuals ≥9 months of age in some countries
  • Booster: Consider at 12-24 months if ongoing exposure

Special Considerations

  • Accelerated schedule for IXIARO: 2 doses 7 days apart for adults 18-65 years old when rapid protection is needed
  • Pregnancy: Inactivated vaccines preferred; live vaccines contraindicated
  • Immunocompromised individuals: Inactivated vaccines recommended; live vaccines contraindicated

Efficacy and Safety of JE Vaccines

Understanding the efficacy and safety profile of JE vaccines is essential for healthcare providers. This section summarizes key data on vaccine effectiveness and potential adverse events.

Efficacy

  • IXIARO: >95% seroprotection after primary series in adults
  • SA14-14-2: 80-96% efficacy in large-scale trials in China
  • IMOJEV: >95% seroprotection in adults and children after a single dose

Duration of Protection

  • IXIARO: Protective antibodies persist for at least 6 years in adults after primary series plus one booster
  • SA14-14-2: Long-lasting immunity demonstrated in endemic areas, potentially life-long
  • IMOJEV: High seroprotection rates maintained for at least 5 years in adults

Safety Profile

  • Inactivated vaccines (e.g., IXIARO):
    • Common reactions: Injection site pain, headache, myalgia, fatigue
    • Rare serious adverse events
  • Live attenuated vaccines (e.g., SA14-14-2):
    • Generally well-tolerated
    • Mild reactions similar to inactivated vaccines
    • Theoretical risk of neurotropic and viscerotropic adverse events (not observed in large-scale use)
  • Chimeric vaccines (e.g., IMOJEV):
    • Safety profile similar to other live attenuated flavivirus vaccines
    • Common reactions: Injection site reactions, headache, myalgia
    • No serious adverse events attributed to the vaccine in clinical trials

Contraindications and Precautions

  • Severe allergic reaction to a previous dose or vaccine component
  • Live vaccines: Pregnancy, immunocompromised status
  • Use with caution in individuals with latex allergy (IXIARO stopper contains latex)

Recommendations for JE Vaccination

Guidelines for JE vaccination vary by country and individual risk factors. This section outlines general recommendations and considerations for vaccine use.

Endemic Country Recommendations

  • World Health Organization (WHO) recommends integration of JE vaccine into national immunization programs in endemic areas
  • Target population: Children in endemic areas, as JE primarily affects young children
  • Catch-up campaigns may be considered for older children and adults in high-risk areas

Traveler Recommendations

  • Consider for travelers to endemic areas, especially:
    • Long-term (>1 month) stays
    • Travel to rural areas or during transmission season
    • Engaging in outdoor activities
  • Vaccination may be considered for shorter-term travelers to areas with ongoing outbreaks
  • Risk assessment should be performed on an individual basis

Occupational Recommendations

  • Laboratory workers at risk of exposure to JE virus
  • Expatriates and long-term travelers in endemic areas
  • Military personnel deployed to endemic areas

Considerations for Vaccine Choice

  • Age of recipient
  • Vaccine availability in the country of use
  • Time available before travel (for accelerated schedules)
  • Previous vaccination history
  • Recipient's health status (e.g., pregnancy, immunocompromise)

Integration with Other Travel Health Measures

  • JE vaccination should be considered alongside other travel health precautions:
    • Mosquito bite prevention (use of repellents, protective clothing, bed nets)
    • Other relevant travel vaccinations (e.g., hepatitis A, typhoid, yellow fever)
    • Malaria prophylaxis if co-endemic


Japanese Encephalitis Vaccines
  1. Q: What type of virus causes Japanese encephalitis? A: Flavivirus
  2. Q: What is the primary vector for Japanese encephalitis virus transmission? A: Culex mosquitoes
  3. Q: Which animals serve as amplifying hosts for the Japanese encephalitis virus? A: Pigs and wading birds
  4. Q: What is the name of the most widely used inactivated Japanese encephalitis vaccine? A: IXIARO (IC51)
  5. Q: How many doses of IXIARO are recommended for primary immunization in adults? A: 2 doses
  6. Q: What is the typical schedule for IXIARO vaccination in adults? A: Days 0 and 28
  7. Q: What is the minimum age for receiving IXIARO vaccine? A: 2 months
  8. Q: How is the Japanese encephalitis vaccine typically administered? A: Intramuscular injection
  9. Q: What is the typical dosage of IXIARO for individuals 3 years and older? A: 0.5 mL
  10. Q: What is the reduced dosage of IXIARO for children aged 2 months to < 3 years? A: 0.25 mL
  11. Q: How long does protection from the primary series of IXIARO typically last? A: At least 1 year
  12. Q: When is a booster dose of IXIARO recommended for adults? A: 1 year after primary immunization if ongoing exposure or re-exposure is expected
  13. Q: What is the name of the live attenuated Japanese encephalitis vaccine used in some Asian countries? A: SA14-14-2
  14. Q: In which year was IXIARO first licensed in the United States? A: 2009
  15. Q: What percentage of people infected with Japanese encephalitis virus develop clinical illness? A: Less than 1%
  16. Q: What is the case fatality rate for symptomatic Japanese encephalitis? A: 20-30%
  17. Q: What percentage of survivors of Japanese encephalitis experience long-term neurological sequelae? A: 30-50%
  18. Q: In which regions is Japanese encephalitis most prevalent? A: South Asia, Southeast Asia, and Western Pacific
  19. Q: What is the typical incubation period for Japanese encephalitis? A: 5-15 days
  20. Q: Which age group is most affected by Japanese encephalitis in endemic areas? A: Children under 15 years old
  21. Q: What is the storage temperature requirement for IXIARO vaccine? A: 2-8°C (35-46°F)
  22. Q: What type of cell culture is used to produce IXIARO vaccine? A: Vero cell culture
  23. Q: How quickly should travelers be vaccinated before potential exposure to Japanese encephalitis? A: At least 1 week before travel
  24. Q: What is the name of the recombinant, chimeric Japanese encephalitis vaccine licensed in Australia and Thailand? A: Imojev (JE-CV)
  25. Q: In which season does Japanese encephalitis most commonly occur in temperate areas? A: Summer and fall
  26. Q: What is the recommended interval between IXIARO doses for accelerated schedules? A: 7 days
  27. Q: Which organ system does Japanese encephalitis primarily affect? A: Central nervous system
  28. Q: What is the estimated global incidence of Japanese encephalitis cases annually? A: 68,000
  29. Q: In which year did the WHO recommend integration of Japanese encephalitis vaccine into national immunization programs in endemic areas? A: 2006
  30. Q: What is the name of the mouse brain-derived Japanese encephalitis vaccine that was previously widely used? A: JE-VAX
  31. Q: How many serotypes of Japanese encephalitis virus exist? A: One
  32. Q: What is the minimum age for receiving the live attenuated SA14-14-2 vaccine? A: 8 months
  33. Q: What is the typical efficacy rate of IXIARO vaccine after completing the primary series? A: Over 95%
  34. Q: How long can protective antibodies persist after vaccination with IXIARO in some individuals? A: Up to 6 years


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