PROTECTION AGAINST HEPATITIS-A BY AN INACTIVATED VACCINE

Objective.-To evaluate the safety and efficacy of a new inactivated he patitis A vaccine. Design.-Double-blind randomized controlled trial st ratified by community. Setting.-Community-based in Thailand. Study Par ticipants.-A total of 40119 children, aged 1 to 16 years, attending 14 8 primary schools: 38157 (95%) entered surveillance a mean of 138 days after receiving vaccine dose 1; 33586 (84%) completed the controlled trial of 532 days; and 31075 (81%) received crossover vaccine and rema ined under surveillance until day 844. Intervention.-Participants rece ived hepatitis A vaccine or control hepatitis B vaccine starting Janua ry 7, 1991 (doses in months 0, 1, and 12), and crossed over to the alt ernate vaccine 18 months later. Main Outcome Measure.-Cases of hepatit is A (symptoms, alanine aminotransferase levels of 45 U/L or higher, a nd IgM to hepatitis A virus) were identified by evaluating school abse nces of 2 or more days. Results.-There were no serious adverse reactio ns despite administration of more than 109 000 doses of hepatitis A va ccine. Among initially seronegative recipients of two doses of hepatit is A vaccine, the proportion with 20 mlU/mL or more of antibody to hep atitis A virus before and 5 months after a 1-year booster was 94% and 99%, respectively. Of 6976 episodes of illness during the controlled t rial, there were 40 cases of hepatitis A; 38 were in the control group . Of the 40 cases, six, all in controls, occurred after the 1-year boo ster dose. Following two doses of hepatitis A vaccine (days 138 throug h 386), protective efficacy was 94% (95% confidence interval, 79% to 9 9%); cumulative efficacy including the postbooster period (days 138 to 532) was 95% (95% confidence interval, 82% to 99%). The two hepatitis A vaccine recipients who had symptomatic infections (257 and 267 days after dose 1) appeared to have been partially protected since their i llnesses were brief and associated with only slight increases in alani ne aminotransferase. Conclusions.-Inactivated hepatitis A vaccine is s afe; when administered in two doses, it protects against hepatitis A f or at least 1 year.