Further evaluation of the safety and protective efficacy of live attenuated hepatitis A vaccine (H2-strain) in humans.

A study on the possibility of transmission of live hepatitis A vaccine (H2-strain) from vaccinees to nonvaccinees was conducted. As a result, no seroconversion was found among 87 seronegative nonvaccinees, who had a close contact with their 141 subcutaneously vaccinated classmates nor was it found among 101 seronegative children administered the vaccine orally. The above fundings suggest that by losing the ability to be transmitted orally the vaccine virus may result in a decreasing possibility of dissemination among contacts. A 4-year study on the protective efficacy of the H2-strain vaccine was done at 11 primary schools starting at 1991 in Shaoxing County. Since then, there has been no hepatitis A reported among 18102 cumulative person-years in the vaccination group, while 495 cases occurred among 242168 cumulative person-years in the control groups. A large scale vaccination with a cumulative vaccination coverage of 89.45% was carried out in Jiaojiang City among children 1-15 years old. Hepatitis A in this age group in the city, which had 12-87 cases per annum with an average of 32 for 8 years before vaccination, decreased drastically to 0-1 cases after vaccination. The protective efficacy of H2-strain vaccine proved to be satisfactory.