A brief history
Japanese encephalitis was first documented in Japan in 1871. It remains an important cause of viral brain inflammation in parts of Asia and the Western Pacific. The name describes where it was recognised, rather than limiting the illness to Japan.
How does it spread?
Infected Culex mosquitoes spread the virus, which circulates between mosquitoes, pigs and water birds. Exposure is often associated with rural farming areas. People generally do not develop enough virus in their blood to infect mosquitoes and continue the transmission cycle.
Symptoms and possible complications
Most infections cause no symptoms or only a mild illness. Rarely, the virus causes encephalitis, with high fever, headache, confusion, seizures or paralysis. Severe disease can be fatal, and survivors may have lasting problems with movement, learning or behaviour. There is no specific antiviral cure; treatment supports the person through the illness.
Where it may be relevant
- Long-stay travellers in risk areas during transmission season
- People spending substantial time in rural, rice-growing or pig-farming areas
- Travellers with extensive outdoor or night-time exposure, even on shorter trips
Dose schedules
The clinician will select the appropriate licensed schedule after reviewing age, health, previous doses and departure date.
Standard course
Age 3 years and over
Rapid adult course
Eligible adults aged 18–65
Complete the course at least seven days before exposure.
Booster
Continuing risk
Timing depends on age, previous course and continuing exposure.
Who may be eligible
- Adults and children from the licensed minimum age whose itinerary creates sufficient risk
- People needing a booster because continuing exposure is expected
Who may not be eligible
- Anyone with a confirmed severe allergic reaction to a previous dose or a vaccine ingredient
- People who are acutely unwell with a significant fever may need vaccination deferred
- Pregnancy, breastfeeding, immune suppression and current medicines must be reviewed individually
Potential side effects
- Pain, redness or swelling where the injection is given
- Headache, tiredness, muscle aches or a mild fever
- Feeling faint around the time of vaccination
Important risks and precautions
- A severe allergic reaction is very rare and requires urgent treatment
- Protection is not absolute, so relevant food, water, bite or exposure precautions remain important
- The exact product and schedule must be confirmed during a clinical assessment
Clinical references