[Epidemiological effects of live attenuated hepatitis A vaccine (H(2)-strain): results of A 10-year observation].

OBJECTIVE

To assess the long-term epidemiological effects after a mass vaccination program, using live attenuated hepatitis A vaccine (H(2)-strain).

METHODS

Shengsi county and Jiaojiang city in Zhejiang province were chosen where high incidence rate of hepatitis A was observed. Mass vaccination program of H(2)-strain vaccine was carried out on 1 - 15 year olds. Cohort studies included two groups were carried out in Shengsi. Cases reported program on hepatitis A was under the national standard on clinical diagnosis and partly through laboratory monitor of anti-HAV IgM and IgG, ELISA and Abbott EIA. Population size was estimated by the yearly reports of census bureau of the county and the city. Serum tests including neutralization test, immune-recall responses, and anti-HAV IgG were performed 10 years after the initial immunization.

RESULTS

The morbidity of hepatitis A was significantly different between vaccinated groups and non-vaccinated groups (P < 0.01) in the cohort study. The protective efficacy in the site was 100 percent. There was a significantly negative correlation of regression between vaccine coverage and hepatitis A morbidity. In both sites, hepatitis A incidence rate showed decrease of 94.5% and 90.3% in whole population, with 96.9% and 97.9% in 1 - 15 year olds respectively. Neutralization test showed that 63.8% of the serum negative to ELISA after vaccination could still neutralize certain HAV. Immune-recall response after the booster was seen in vaccine group with 80.2% positive rate of anti HAV-IgG, 10 years after immunization among vaccinees in both sites. Not a single hepatitis A case was identified.

CONCLUSION

Live attenuated hepatitis A vaccine seemed to have obviously long-term epidemiological effects.