Japanese Encephalitis in a Nutshell
(source: Health and Immunization for Children pamphlet published by the Bureau of Public Health, Tokyo Metropolitan Government, pages 12, 13,18, & 24, March 1998 and Dr. Matsuki at the Bureau)
Japanese Encephalitis [nihon nooen] is a virus. This virus harbors in pigs and is transferred to humans via mosquitoes. Many people develop no symptoms and are not in danger. Only 1/1000 to 1/5000 exposed persons will develop symptoms. After a 7-10 days incubation period the following symptoms may be noted: high fever, vomiting, unconsciousness and convulsions. It is found throughout Japan except Hokkaido, but more often reported in Western Japan. The disease among pigs is seasonal from approximately June to October, About 80% of virus infection in the pork population occurs during these months.
Adults of 60 years and over and children of 5 years and younger are most vulnerable. The case fatality rate is around 15%. Fifty percent of infected persons will suffer affects on their nervous systems. In rare cases the following symptoms have been reported: aseptic meningitis, "summer cold".
In 1998 there were 4 cases reported in all of Japan*, none in Tokyo, and the incidence among school children has decreased. These low figures are attributed to the immunization program. Immunization is strongly mandated in Japan after 3 years of age. The basic vaccination consists of three doses. One to four weeks pass between the first and second dose. About one year passes before the third dose. Boosters can be received every 4-5 years after. Health regulations allow for immunization to begin as early as 6 months of age, but the vaccine is commonly started at about 3 years of age.
If you are in the high risk age groups and not vaccinated, try to avoid mosquitoes. Wear long sleeves, sleep under a mosquito net, and use repellants.
The vaccine is refined, non-active. Less than one out of 100 children might have a fever of more than 37.5 C within two days after vaccination, and less than 1-3 out of 100 might have swelling at the injection site. Rash and dull pain have also been reported in a few cases.
Japanese Encephalitis is also found in China, India, Thailand, Vietnam, Nepal and Sri Lanka.
Designated immunizations are provided as a part of the Public Health System but are not covered under National Health Insurance directly.
Immunizations are given by municipal city offices and details are sent by mail or by circular. Letters will be sent to all persons whose name is registered on residential lists or alien registration lists. If you or a child is not registered, or incorrectly registered (wrong address), you may not receive the notice. In that case you can go to the appropriate section of the city office and receive the information directly. It is generally better to take an immunization slightly earlier rather than slightly past the prescribed period, if for some reason you are unable to do so at the prescribed time. The details concerning the time and place for receiving the immunization will be in the notice. In some cases (polio for example) the procedure will take place in a group setting in pre-designated locations. In other cases you will receive a "coupon" that can be used at a pediatrician or clinic convenient to you. In all cases bring along your Mother and Child Health Handbook [Boshi Techo].
*There has been no death from Japanese encephalitis since 1969 in Tokyo. The recent patient numbers (not fatality numbers) are as follows.
CDC Travel Information: Japanese Encephalitis Information for Travelers
Virtual Hospital: Travel Medicine: Immunizations and Chemoprophylaxis for Travel-Related Diseases
Travel Health Online: Japanese Encephalitis - Traveler Information
Health Protection Branch - Laboratory Centre for Disease Control: STATEMENT ON JAPANESE ENCEPHALITIS VACCINE
Health Matters: Japanese Encephalitis
NHMRC Media Release: JAPANESE ENCEPHALITIS VACCINE ADDED TO IMMUNISATION SCHEDULE
FDA: The licensing of a vaccine against Japanese encephalitis (12/18/1992)
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