What is the recommended vaccination strategy for Japanese encephalitis?

Japanese Encephalitis Vaccination Recommendations

Japanese encephalitis vaccine is strongly recommended for travelers spending a month or longer in endemic areas during transmission season, and should be considered for short-term travelers who plan to travel outside urban areas. 1

Vaccination Schedule by Age Group

The recommended vaccination schedule for Japanese encephalitis virus vaccine (JE-VC) varies by age:

• 2-35 months: 2 doses (0.25 mL each) administered intramuscularly (IM) on days 0 and 28
• 3-17 years: 2 doses (0.5 mL each) administered IM on days 0 and 28
• 18-65 years: 2 doses (0.5 mL each) administered IM on days 0 and 7-28 (only age group for which an accelerated schedule is approved)
• >65 years: 2 doses (0.5 mL each) administered IM on days 0 and 28 1

For all age groups, the 2-dose series should be completed at least 1 week before potential exposure to JE virus to ensure adequate protection 1, 2.

Risk Assessment Algorithm for Vaccination

1. Definite recommendation for vaccination:

   • Laboratory workers with potential exposure to infectious JE virus
   • Travelers moving to a JE-endemic country to take up residence
   • Travelers planning longer-term (≥1 month) travel to JE-endemic areas
   • Travelers with frequent travel to JE-endemic areas 1

2. Consider vaccination for:

   • Short-term travelers (<1 month) to endemic areas during transmission season if traveling outside urban areas with activities increasing risk of exposure
   • Travelers to areas with ongoing JE outbreaks
   • Travelers to endemic areas with uncertain specific destinations, activities, or duration 1

3. Vaccination not recommended for:

   • Short-term travelers whose visits will be restricted to urban areas
   • Travel outside of a well-defined JE virus transmission season 1

Vaccine Efficacy and Immunogenicity

The JE-VC vaccine (IXIARO) demonstrates excellent immunogenicity across all age groups:

• In children receiving age-appropriate dosing, seroconversion rates reach ≥99.2% at 56 days after the first dose 3
• In adults, seroconversion rates of 96-99% are achieved after completing the 2-dose series 1
• Protection persists in 85.5-100% of subjects at 7 months post-vaccination 3
• The accelerated schedule (0 and 7 days) for adults 18-65 years shows 99% seroprotection at 28 days and 94% at >300 days 1

Simultaneous Administration with Other Vaccines

JE-VC can be administered simultaneously with other vaccines:

• No interference with immune response when given with hepatitis A vaccine 1
• Noninferiority of immunological responses when given with rabies vaccine 1
• When administered concomitantly with other vaccines, use separate syringes and different anatomical sites (>1 inch apart if possible) 1

Special Populations and Precautions

1. Pregnancy: Pregnancy is a precaution for JE-VC use. Vaccination should generally be deferred due to theoretical risk to the developing fetus. However, pregnant women who must travel to high-risk areas should be vaccinated if benefits outweigh risks 1.

2. Infants: Safety and effectiveness not established for infants <2 months of age 1.

3. Allergies: Severe allergic reaction (e.g., anaphylaxis) to a previous dose of JE-VC, any other JE vaccine, or any component of JE-VC (including protamine sulfate) is a contraindication 1, 2.

Booster Doses

• For individuals ≥17 years who have received a primary immunization series more than 1 year previously, a booster dose may be given if ongoing exposure or re-exposure to JEV is expected 2.
• Clinical trial data show high rates of seroprotection for at least 6 years after a booster dose 1.

Practical Considerations

• Before administration, shake the syringe well to obtain a white, opaque, homogeneous suspension 1.
• For 0.25 mL pediatric dose, expel and discard half of the volume from the 0.5 mL prefilled syringe by pushing the plunger stopper up to the edge of the red line on the syringe barrel 1, 2.
• All travelers to JE-endemic countries should take precautions to avoid mosquito bites to reduce the risk for JE and other vector-borne diseases, regardless of vaccination status 1.

Importance of Vaccination Despite Declining Cases

Despite reduced numbers of vector mosquitoes and patients in some areas, studies show that JE virus remains present and active in nature, with annual infection rates of 1.3-2.6% even in countries like Japan with previously high vaccination rates 4. This underscores the continued importance of vaccination for at-risk populations.