A Cluster of Severe Reactions Following Improperly Administered Takeda Japanese Encephalitis Vaccine.

Japanese encephalitis (JE) is an infection caused by a mosquito-transmitted virus present in many parts of Asia, including India, and Oceania. Infection is usually asymptomatic, leading to overt encephalitis in only 0.1-5% of infected individuals. When encephalitis occurs it is usually severe, with a 25% fatality rate, and 30% of cases resulting in permanent neurologic deficiencies. Since 1981, eight cases of JE have occurred in United States (U.S.) military personnel and their dependents stationed overseas.1 JE vaccine manufactured by Biken (Research Institute for Microbial Diseases, Osaka, Japan) is given to certain military personnel assigned to endemic areas in Asia. Concern about vaccine-associated hypersensitivity reactions has limited more widespread use. We report three cases of severe hypersensitivity following JE vaccination with a non-Biken JE vaccine (Takeda) under unusual circumstances.