A disease of viral origin, it is the leading cause of encephalitis in a 24-country area that includes more than 3 billion people in Southeast Asia and the Western Pacific. It is transmitted by the bite of infected mosquitoes and generally does not cause symptoms. 1% of cases develop headache, fever and nausea, which can develop into convulsions and paralysis. It is fatal in 30% of severe cases.

Although the risk is small, the disease mainly affects children, and in severe cases up to 30% percent of survivors may manifest neurological or psychiatric deficiencies.

The vaccine cycle consists in the administration of 2 doses, the second administered 28 days after the first. A booster is recommended within 2 years after the end of the cycle, or 1 year if you are at continued risk of infection. There is a "shortened" cycle that provides the second dose 7 days after the first. The cycle should be finished at least one week before potential exposure to the virus.

Inactivated virus vaccine administered intramuscularly. It can be administered from the age of two months. Use in pregnant or breast-feeding women should be assessed by a physician.