Transmissionof Japanese Encephalitis(JE) Virus in Gia Luong District, Ha Bac Province, Vietnam,After Je Vaccination,1993-1994

A total of 15,183childrenunder 10 years old (37%of target population)was im- munizedwith JE vaccinein GiaLuongDistrict, Ha BacProvince,Vietnam,in 1993to 1994.JE virus transmissionwas investigatedby swine antibody survey and virus isolationfrom field mosquitoes.By the hemagglutinationinhibition (HI) test, 73-90% of swine were antibody positiveall yearround,with high geometricmeantiter (GMT)of 92.67-95.14 in Mayand June. Bysucklingmousebrain inoculation,6 JE virus strains were isolated from Culextritaeniorhyn- chus and Cx.vishuni,as well as laboratoryreared F1 from field-caughtCx. tritaeniorhynchus. Serodiganosisby IgM-capture ELISA (MAC-ELISA) carried out on 60 of 85 clinical en- cephalitiscases detected 43 positives(71.66%).Allthese serologicallyconfirmedJE caseshad not beenvaccinated.The results supportedthe vaccineefficacyto prevent overt JE.