Japanese Encephalitis Immunization Program In South Korea: Time to Move Forward

Background: Japanese encephalitis (JE) is the leading cause of viral encephalitis among children in Asia. South Korea had several epidemics of JE in 20^th century; however, due to vigorous immunization programs, it has successfully controlled the disease since 1990s.

Setting: Mouse brain-derived inactivated JE vaccine which was introduced in the country in 1971 has been used as one of NIP vaccines along with live attenuated SA 14-14-2 JE vaccine which has been on the market since 2002. National immunization guideline recommends 3 doses of primary series of inactivated JE vaccines starting from 12 months of age and 2 booster doses at 6 years and 12 years, respectively.

Population: Due to the endemicity of JE and long-standing immunization programs, Korean population has been regarded to have immunity against JE.

Project Description: JE is one of the notifiable diseases under the Communicable Disease Prevention Act and since 1990 there were less than 10 JE cases annually. This year (2010), however, almost 30 confirmed JE cases have been reported so far. Most of the cases are in their 40s and 50s, some of which have no identifiable risk factor of acquiring JE viruses. Several reasons have been suggested to explain the sudden increase of patients such as climate change and decreased immunity level of the population, none of which have been proved yet.

Results/Lessons Learned: Even though JE has been traditionally regarded as children’s disease, in countries where strong immunization program exists like South Korea, the majority of the JE patients are adults. Since the immunization program is targeted at children under the age of 15 and natural boostering effect has been minimal due to the decreased disease burden, seroprevalence research for adults, followed by discussion for adult immunization policy should be considered in the near future.