PROTECTION AGAINST HEPATITIS-A BY AN INACTIVATED VACCINE

Objective.-To evaluate the safety and efficacy of a new inactivated hepatitis A vaccine. Design.-Double-blind randomized controlled trial stratified by community. Setting.-Community-based in Thailand. Study Participants.-A total of 40119 children, aged 1 to 16 years, attending 148 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 remained under surveillance until day 844. Intervention.-Participants received hepatitis A vaccine or control hepatitis B vaccine starting January 7, 1991 (doses in months 0, 1, and 12), and crossed over to the alternate vaccine 18 months later. Main Outcome Measure.-Cases of hepatitis A (symptoms, alanine aminotransferase levels of 45 U/L or higher, and IgM to hepatitis A virus) were identified by evaluating school absences of 2 or more days. Results.-There were no serious adverse reactions despite administration of more than 109 000 doses of hepatitis A vaccine. Among initially seronegative recipients of two doses of hepatitis A vaccine, the proportion with 20 mlU/mL or more of antibody to hepatitis A virus before and 5 months after a 1-year booster was 94% and 99%, respectively. Of 6976 episodes of illness during the controlled trial, 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 booster dose. Following two doses of hepatitis A vaccine (days 138 through 386), protective efficacy was 94% (95% confidence interval, 79% to 99%); 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 illnesses were brief and associated with only slight increases in alanine aminotransferase. Conclusions.-Inactivated hepatitis A vaccine is safe; when administered in two doses, it protects against hepatitis A for at least 1 year.