Protective efficacy of H2 strain live attenuated hepatitis A vaccines in an outbreak of hepatitis A

Objective To investigate the protective efficacy of H 2 strain live attenuated hepatitis A vaccine (H 2 strain vaccine) locally produced in an outbreak of hepatitis A (HA). Methods A nonrandomized controlled design was used in a trial for HA vaccination. Five thousand five hundred and fifty one children at preschool classes and at grades 1～3 of primary schools were selected in 14 villages. Epidemiological and serological methods were used to evaluate its protective efficacy of the vaccines and serum immunoglobulin M against hepatitis A virus (IgM anti HAV) was detected with ELISA for 271 subjects in vaccinated group and 341 in the control one. Results An outbreak of HA occurred one year after the vaccination with 26 cases in the vaccinated group, including one vaccine related case with an attack rate of 0.28% (1/356), and 25 cases in the control group with an attack rate of 5.92% (25/422). The protective efficacy of vaccines was 95 27% (95% confidence interval of 85 83% to 104 72%) Positivity of IgM anti HAV, i.e., newly infected cases, was 4 43% (12/271) in the vaccinated group and 13 38% (42/314) in the control group, respectively. Clinically apparent cases accounted for 8 33% (1/12) and 50 00% (21/42) in newly infected cases in vaccinated and control groups, respectively. Conclusion Vaccination with H 2 strain vaccines locally produced was effective in reducing occurrence of HA during its outbreak, but not so effective in preventing its infection. A booster dose of HA vaccine should be vaccinated for children in adequate time.