What is Japanese Encephalitis?

Japanese encephalitis virus is primarily transmitted by Culex mosquitoes, particularly Culex tritaeniorhynchus. It is prevalent in Asia and the Western Pacific, where infections may be asymptomatic but severe cases can lead to encephalitis, paralysis, or death. According to the World Health Organization (WHO), there are tens of thousands of cases globally each year.

In Hong Kong, local cases are rare, but residents near pig farms face a 20-fold higher risk. The Centre for Health Protection estimates that up to 633,000 people are affected, mainly in the New Territories West. Prevention focuses on avoiding mosquito bites and vaccination.

Vaccination Schedule

For Children Aged 9 Months to 17 Years:

• Primary Dose: Single subcutaneous injection.
• Booster: 12-24 months after primary dose.

For Adults Aged 18 and Above:

• Primary Dose: Single injection.
• Booster: As needed, 12-24 months apart.

Vaccination should be administered by healthcare professionals, following Hong Kong’s Reference Framework for Preventive Care for Children.

Transmission Risks and Prevention in Hong Kong

Based on the Food and Environmental Hygiene Department’s 2004-2005 survey, Culex tritaeniorhynchus is widely distributed in Hong Kong. The Centre for Health Protection’s 2017 consensus statement recommends:

• Priority vaccination for residents within 2 km of pig farms.
• Enhanced environmental monitoring, such as eliminating standing water to reduce mosquito breeding.
• Use of insect repellents (e.g., DEET) and wearing long-sleeved clothing.

Prevention Tips:

• Avoid outdoor activities at dusk and dawn.
• Exercise caution near pig farms or rural areas.