WHAT IS JAPANESE ENCEPHALITIS?
Japanese Encephalitis (JE) is a mosquito-borne arboviral infection and is the leading cause of viral encephalitis in Asia. It is transmitted in a cycle between Culex mosquitoes and certain animals (chiefly domesticated pigs and wading birds), humans are an incidental host.
Risk for acquiring JE among most travelers to Asia is extremely low; however, the risk of transmission is higher in rural areas, especially where pigs are raised and where rice paddies, marshes and standing pools of water provide breeding grounds for mosquitoes and feed for birds. Risk for an individual traveler is highly variable and depends on factors such as the season, locations and duration of travel, and activities of the traveler.
Infections with JE lead to encephalitis in only 1 of 300 cases, with a fatality rate of 25% and neuropsychiatric sequelae in 30% of cases. Limited data indicate that JE acquired during the first or second trimesters of pregnancy causes intrauterine infection and miscarriage. Infections during the third trimester of pregnancy have not been associated with adverse outcomes in newborns. Advanced age may also be a risk factor for developing symptomatic illness after JE infection.
JAPANESE ENCEPHALITIS VACCINE (JE-VAX):
Japanese Encephalitis Virus Vaccine is an inactivated virus vaccine derived from infected mouse brain. Thimerosal is added as a preservative. Studies have shown this vaccine to be 70%-97% effective in preventing disease.
JE vaccine is recommended for persons who plan to reside for a month or longer in areas where JE virus is endemic or epidemic (residence during a transmission season). In general, vaccine should be considered for use in persons spending a month or longer in epidemic or endemic areas during the transmission season, especially if travel will include rural areas. Depending on the epidemic circumstances, vaccine should be considered for persons spending less than 30 days whose activities, such as extensive outdoor activities in rural areas, place them at particularly high risk for exposure.
Vaccination poses an unknown but theoretical risk to the developing fetus, and the vaccine should not be routinely administered during pregnancy. However, because JE infection acquired during pregnancy carries the potential for intrauterine infection and miscarriage, the risk of JE infection to the mother and developing fetus should be weighed against the theoretical risks of immunization for pregnant women who will travel to areas where JE is prevalent.
For persons over 3 years of age, the recommended primary immunization series is three 1.0 ml doses given at 0, 7, and 30 days. For children 1 - 3 years of age a series of three doses of 0.5 ml should be given at 0, 7, 30 days. There is no information on the efficacy of JE vaccine in infants under one year; vaccination should be deferred until at least one year of age whenever possible.
An abbreviated schedule of 0, 7, 14 days can be used when the longer schedule is impractical due to time constraints. The last dose should be given at least 1 0 days before beginning international travel to ensure an adequate immune response and access to medical care in the event of a delayed adverse reaction.
According to Centers for Disease Control and Prevention, antibodies to JE virus persist for at least 3 years after primary immunization. Therefore, if a booster dose is given, it should be at least 3 years after completion of the primary immunization series.
POSSIBLE SIDE EFFECTS FROM THE VACCINE:
20% of people receiving this vaccine report localized tenderness, redness and swelling. Fever, headache, fatigue, rash, and other reactions such as chills, dizziness, muscle aches, nausea, vomiting, and abdominal pain have been reported in about 10% of persons receiving the vaccine. In Japan during 1965-73 neurologic events (encephalitis, encephalopathy, and seizures) were noted in 1 of every 2.3 million vaccinees.
A new pattern of adverse events has been noted since 1989 including hives, swelling of the limbs, face and oropharynx (especially lips), respiratory distress, low blood pressure and joint pain. Symptoms after the first dose have generally occurred within 12 hours, the second dose 3 days, and the third up to 2 weeks later.
WARNING: WHO SHOULD NOT TAKE THE VACCINE:
If you have any questions about Japanese Encephalitis or Japanese Encephalitis Vaccine, please ask us now or call your doctor before you receive the vaccine.
Note to UWMC/HMC patients: If you have questions on this information, please consult your UWMC/HMC health care provider.
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