Japanese Encephalitis Vaccine Recommendations
The Japanese Encephalitis vaccine (JE-VC) is recommended for travelers with longer-term stays (≥1 month) in endemic areas, those moving to endemic countries, or frequent travelers to these regions, administered as a 2-dose intramuscular series that must be completed at least 1 week before potential exposure. 1
Who Should Receive the Vaccine
Definite Indications
- Moving to a JE-endemic country to take up residence 1
- Longer-term travel (≥1 month) to JE-endemic areas 1
- Frequent travel to JE-endemic areas 1
- All laboratory workers with potential exposure to JE viruses (except those working only with SA14-14-2 vaccine virus) 1
Consider Vaccination For
- Shorter-term travel (<1 month) with increased risk based on rural location, transmission season, outdoor activities (especially sunset through dawn), and accommodations without air conditioning, screens, or bed nets 1
- Travel to JE-endemic areas with uncertain duration, destination, or activities 1
Do NOT Vaccinate
- Very low-risk travelers with shorter-term travel limited to urban areas OR travel outside well-defined JE virus transmission seasons 1
Primary Vaccination Schedule
Age-Specific Dosing (Intramuscular Administration)
- Ages 2-35 months: 2 doses of 0.25 mL each on days 0 and 28 1
- Ages 3-17 years: 2 doses of 0.5 mL each on days 0 and 28 1
- Ages 18-65 years: 2 doses of 0.5 mL each on days 0 and 7-28 (accelerated schedule available) 1
- Ages >65 years: 2 doses of 0.5 mL each on days 0 and 28 1
Critical Timing
- Complete the 2-dose series at least 1 week before potential JE virus exposure 1
Vaccine Preparation and Administration
Preparation
- Shake the syringe well to obtain a white, opaque, homogeneous suspension (vaccine may appear as clear liquid with white precipitate during storage) 1
- For 0.25 mL doses: Expel and discard half the volume from the 0.5 mL prefilled syringe by pushing the plunger stopper to the edge of the red line 1
- Store at 35°F-46°F (2°C-8°C), do not freeze, protect from light 1
Administration Technique
- Administer intramuscularly at 90-degree angle 2
- Preferred sites: Deltoid muscle for adults and older children; anterolateral thigh for infants and younger children 2
- Use separate syringes and different anatomical sites (>1 inch apart if possible) when administering concomitantly with other vaccines 1
Booster Doses
- A single booster dose (0.25 mL for ages 2-35 months; 0.5 mL for ≥3 years) may be given if ongoing risk exists and ≥1 year has elapsed since primary series 1
- Clinical trial data show high seroprotection rates for at least 6 years after a booster dose 1
- No U.S. recommendations exist for subsequent booster doses beyond the first 1
Contraindications and Precautions
Absolute Contraindications
- Severe allergic reaction (anaphylaxis) after previous JE vaccine dose or any vaccine component 1
- Known hypersensitivity to protamine sulfate (contained in JE-VC) 1
Precautions
- Pregnancy: Usually defer vaccination due to theoretical fetal risk; however, vaccinate pregnant women traveling to high-risk areas when benefits outweigh risks 1
- Infants <2 months: Safety and effectiveness not established 1
- Adults ≥65 years: Lower seroprotection rates and GMT compared to younger persons, though no data support additional or early booster doses 1
- Immunocompromised persons: May have diminished response; no specific data available 1
Not Contraindications
- Breastfeeding: Not a contraindication or precaution 1
Adverse Events and Safety Monitoring
Common Side Effects
- Approximately 50% of vaccinees experience usually mild adverse effects 3
Serious Allergic Reactions
- Generalized urticaria and angioedema can occur from minutes to 2 weeks after vaccination 1
- Rates of serious allergic reactions are low (1-104 per 10,000) 1
Safety Measures
- Observe vaccinees for 30 minutes after vaccination 1
- Warn patients about possibility of delayed urticaria and angioedema of head and airway 1
- Advise vaccinees to remain in areas with ready access to medical care for 10 days after vaccination 1
- Have epinephrine and equipment to treat anaphylaxis available 1
Reporting
- Report all clinically significant adverse events to VAERS (https://vaers.hhs.gov or 800-822-7967), even if causal relation uncertain 1
Concomitant Vaccine Administration
- JE-VC can be administered concomitantly with hepatitis A vaccine without interference 1
- JE-VC can be administered concomitantly with rabies vaccine with noninferiority established 1
- Use separate syringes and different anatomical sites (>1 inch apart if possible) for concomitant administration 1
Risk Assessment Factors
Geographic Risk
- Highest risk in rural or agricultural areas with flooded rice fields, marshes, and stagnant water collections 1
- Cases reported among travelers to coastal areas or resorts adjacent to rural/rice-growing areas 1
- Risk varies within countries and from year to year 1
Temporal Risk
- Transmission occurs seasonally in some areas, year-round in others 1
- Mosquitoes feed most often outdoors from sunset through dawn 1