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 h ad a close contact with their 141 subcutaneously vaccinated classmates nor was it found among 101 seronegative children administered the vac cine orally. The above findings suggest that by losing the ability to be transmitted orally the vaccine virus may result in a decreasing pos sibility of dissemination among contacts. A 1-year study on the protec tive efficacy of the H2-strain vaccine was done at 11 primary schools starting at 1991 in Shaoxing County. Since then, there has been no hep atitis A reported among 18102 cumulative-person-years in the vaccinati on group, while 495 cases occurred among 242168 cumulative person-year s in the control groups. A large scale vaccination with a cumulative v accination 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, wh ich had 12-87 cases per annum with an average of 32 for 8 years before vaccination, decreased drastically to 0-1 cases after vaccination. Th e protective efficacy, of H2-strain vaccine proved to be satisfactory. (C) 1997 Elsevier Science Ltd.