South Korea Issues Nationwide Japanese Encephalitis Alert

South Korea’s Korea Disease Control and Prevention Agency (KDCA) has issued a nationwide alert for Japanese encephalitis (JE), a mosquito-borne viral infection, following the early detection of Culex tritaeniorhynchus mosquitoes – the primary vectors for the disease. The alert, initially issued on March 20, 2026, comes as climate change appears to be accelerating the emergence of these mosquitoes.

Understanding Japanese Encephalitis

Japanese encephalitis is a significant public health concern in Asia and the Western Pacific region, including South Korea. The virus is transmitted to humans through the bite of infected mosquitoes, primarily Culex tritaeniorhynchus. These mosquitoes are widespread throughout the country, breeding in rice paddies, livestock sheds and stagnant water [1].

Early Detection and Climate Change Impact

The KDCA’s surveillance program, in cooperation with regional centers and the Ministry of National Defense, detected the first JE vector mosquito of the year in Jeju Special Self-Governing Province. Just two days into monitoring, one Culex tritaeniorhynchus mosquito was identified among a collection of 18. The average temperature in Jeju Province (February 16 to March 15) was 0.8°C higher than the previous year, with a 1.1°C increase in the average maximum temperature, suggesting an earlier start to the mosquito season [1].

Symptoms and Risks

Initial symptoms of Japanese encephalitis are often mild, including fever, headache, and vomiting. Yet, the disease can progress to encephalitis, a more severe condition characterized by high fever, seizures, confusion, convulsions, paralysis, and disorientation. Approximately 20-30% of patients who develop encephalitis may die, and 30-50% of survivors experience long-term neurological complications [3].

Who is at Risk?

Over the past five years (2020-2024), 90% of the 79 reported Japanese encephalitis cases in South Korea were among individuals aged 50 or older [3]. Men are also more likely to be affected, accounting for 60.8% of cases [1]. Those living near rice paddies or pig farms, or planning to spend time in these areas during the transmission season, are at increased risk.

Prevention and Vaccination

An effective vaccine against Japanese encephalitis is available. The KDCA recommends that children eligible for the national immunization program (those born after 2013) receive the vaccine according to the standard schedule. Vaccination is also recommended for adults aged 18 or older who have not previously been vaccinated, particularly those in high-risk areas or those planning extended stays in JE-endemic countries [3].

KDCA Response and Control Measures

Commissioner Lim Seung-kwan of the KDCA has urged the public to follow mosquito bite prevention guidelines and ensure children receive their vaccinations. The agency is also emphasizing the importance of comprehensive mosquito control measures, including identifying and managing vulnerable areas with high larval outbreaks to reduce vector mosquito density [1].

Recent Cases

The first cases of Japanese encephalitis in South Korea for 2024 were confirmed in March, involving a man and a woman in their 60s from Daegu and South Gyeongsang Province, respectively. Both patients had been engaged in outdoor activities at night and had not been vaccinated [4].