Objective: To study two live vaccines, H2 and LA-1 strains, both attenuated in growth on human diploid cell culture at lower temperature (32 degrees C).
Methods: Randomized, controlled trials were performed among half million children. 135,340 children were divided into vaccine or control groups by individual and 360,012 by cluster. Those susceptibles with negative anti-HAV were bled at 2-6 months after the vaccination and blood test for anti-HAV.
Results: 37 hepatitis A cases were found in the control group. The protective efficacy of the two vaccines was 100%, and the 95% lower confidence limit (one sided) of combined efficacy of the two vaccines was 92.1%, that was comparable with the two inactivated vaccines produced by SmithKline beecham or Merck Sharp Dhome.
Conclusion: The vaccines are safe, and the seroconversion to H2 strain (10(7.0) TCID50) and LA-1 strain (10(6.75) TCID50) is 94.87% and 83.16% respectively.