Objective   To detemine the type of vaccine for streng thening immunity on the basis of fundamental immunity 1 year ago with biovalent inactivated vaccine against HFRS, by comparing the antibody response level after strenghening immunity with bivalent, typeⅠand typeⅡunivalent vaccine, respectively.

  Methods   Serum samples were taken from 206 vaccinated objects after 2 weeks later(after fundamental immunity), 1 year later(before strenghening immunity), 2 weeks and 1 year later(after strengthening immunity), respectively.Indirect immu noflu orescence test and MCPEBT were used to assay IFA-IgG antibody and neutralizing antibody.

  Results   (1) Two weeks later(after fundamental immunity), positive rate of IFA-IgG antibody was 96.76% and geometrical mean titration(GMT)was 38.05.Positive rate of neutralizing antibody was 100% for typeⅠ, and 92.50% for typeⅡ.GMT of neutralizing antibody was 20.82 for typeⅠ, and 15.66 for type Ⅱ.(2)One year later(before strengthening immunity), positive rate and GMT of IFA-IgG antibody decreased to 51.91% and 25.45, respectively.Positive rate of neutr alizing antibody was 55.81% for typeⅠ, and 46.51% for typeⅡ.GMT of neutralizing antibody was 5.45 for typeⅠ, and 5.18 for typeⅡ.(3)Two weeks later(after strenghening immunity), positive rate of IFA-IgG antibody increased to 98.46%, and GMT also increased to 38.02.Meanwhile, positive rate of two types of neutr alizing body were all 100% in three groups.GMT of typeⅠ antibody was 20.01, 46.66 and 12.42 in the corresponding group, respectively.GMT of typeⅡ antibody was 20.00, 19.99 and 16.82 in the corresponding group, respectiv ely.

  Conclusion   By strenthening immunity with either type of vaccine on the basis of fundamental immunity with bivalent vaccine, positive rate and GMT of both IFA-IgG antibody and neutralizing antibody in three groups were very approximate.But GMT of typeⅠneutralizing antibody in typeⅠ univalent vaccine group was the highestin three groups.It was indicated that on the basis of fundamental immunity with bivalent vaccine, strengthening immunity with univalent vaccine, the type being the same with the focus type, would be recommendable for the benefit of less economic burden on objects of vaccination.