An evaluation of the serological and epidemiological effects of the outer envelope vaccine to leptospira.

BACKGROUND

The Shanghai Institute of Biological Products manufactured successfully a new outer envelope vaccine for leptospira in 1978. It has been confirmed by using animal tests and a number of human body trials that this vaccine is safe and effective, However, results regarding serological and epidemiological effects of the vaccine in population has not been reported. The objective of this study was to evaluate serological and epidemiological effects of this vaccine.

METHODS

From May 1998 to May 1999, an evaluation of the serological and epidemiological effects of the outer envelope vaccine for leptospira made by Shanghai Institute of Biological Products was conducted among agricultural population aged 5 to approximately 60 years in an epidemic area of leptospirosis, in Jingzhou District, Jingzhou City, Hubei Province, China by microscopic agglutination test (MAT), cohort study, matched case-control study and screening method.

RESULTS

The serological surveillance results of 77 students immunized showed that the successful rates of vaccination with the outer envelope vaccine of L. icterohaemorrhagiae sero-group and L. hebdomadis sero-group leptospira were 79.22% and 77.92%, respectively, the antibody geometric mean titer (GMT) of the two groups were 1:106.71 and 1:63.31, respectively, with 6.7-fold and 4.7-fold rises comparing with the group of those of the antibody before inoculation, and the antibody protective rates of the two groups of outer membrane protein vaccine of leptospira all were 100% at one month after immunization. Higher level antibody against L. icterohaemorrhagiae sero-group leptospira was still maintained at one year after injection. The results of cohort analysis showed that the protective rate of the outer envelope vaccine of leptospira for the same serological groups of leptospira was 75.17%, and the effective index of the vaccine was 4.03. The protective rate of vaccines obtained from 1:2 matched case-control studies was 81.25%, while that estimated by screening method was 75%.

CONCLUSIONS

The study results showed that the serological and epidemiological efficiencies of leptospira vaccine all were ideal. In addition, this vaccine had partly protective effect against other sero-groups of leptospira.