Australian Case-Control Study of Adverse Reactions to Japanese Encephalitis Vaccine

Background: Japanese encephalitis (JE) is widely distributed in Asia and is the world's most common aborviral encephalitis. An effective vaccine against JE has been used in Asia for decades without reports of serious adverse reactions. Since 1989, an apparent increase in frequency of allergic reactions to JE vaccine has been reported from a number of nonendemic countries, including Australia. The objective of this study was to evaluate possible risk factors for allergic reactions associated with Japanese encephalitis (JE) vaccine. Methods: A case-control study was carried out in Australia. Subjects were persons who had developed an allergic reaction (rash and/or edema) that had occurred within 1 week of a dose of Biken JE vaccine. All cases had been reported to the Australian Adverse Reactions Advisory Committee, and all could be accessed for purposes of this study. Three matched controls were recruited for each of five cases. Participants completed a questionnaire and had venous blood drawn. Results: Cases were significantly less likely than controls to give a history of contact with dogs (Fisher's exact test p =.03); were more likely than controls to have received other immunizations in the 1-9 days prior to, rather than on the same day, as the JE vaccine (chi-square test for independence p =.015); and were more likely than controls to have consumed more than usual quantities of alcohol in the 48 hours following the last dose of JE vaccine (Fisher's exact test p =.034). Conclusions: We recommend, where possible, that JE vaccine be administered concurrently with other vaccines, that recipients be advised to avoid more than usual alcohol intake after receiving JE vaccine, and that active surveillance of adverse events associated with JE vaccine be conducted.