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[A field evaluation of the epidemiological efficacy of an attenuated live hepatitis A vaccine (H2 strain)].

OBJECTIVE
To evaluate the epidemiological efficacy of an attenuated live hepatitis A vaccine (H2 strain).


METHODS
A randomized and controlled field trial was carried out in part of Zhengding County and the Jiaoqu District of Shijiazhuang city. There were about 37,000 children in these areas involved in the study and they were randomly divided into a vaccine group and a control group according to the months they were born. Children in the vaccine group were given a dose of 10(6.5) TCID50/ml attenuated live hepatitis A vaccine while those in the control group were given nothing. As soon as the children in the vaccine group had been vaccinated, all the subjects were carefully followed up for hepatitis A cases.


RESULTS
In the 3.5 years of follow-up, there were 20 hepatitis A cases in the control group and the incidence rate was 136.4 per 100,000 population. There was only one hepatitis A case in the vaccine group and the incidence rate was 8.1 per 100,000 population. The difference of the incidence rates between the two groups was highly significant (P < 0.001) and the protective efficacy of the vaccine was 94.4% (95% CI: 67.1%-100%).


CONCLUSION
The protective efficacy of the vaccine was excellent and the vaccine is suitable to be widely used.