Assessment of long-term efficacy of hepatitis B vaccine.

In a healthy cohort of 462 subjects in which hepatitis B vaccine was administered between 1990 and 1992 a follow-up study was carried out to determine the duration of protection. Individuals with antibody against the hepatitis B virus surface antigen (anti-HBs) titer lower than 100 mIU/ml were administered a booster dose and antibodies determined 30 days later. The proportion of protection 6.5 years after vaccination was 85% (95% CI: 82-88). Only nine vaccinees seroconverted to anti-HBc positivity without becoming carrier or ill. In 125 subjects in which a booster dose was administered a significant increase in geometric mean of anti-HBs titer was observed (609 mIU/ml) as compared to late (13 mlU/ ml) and early post-vaccination antibody levels (256 mIU/ml, Wilcoxon's test, p < 0.001) suggesting the existence of an anamnestic response. We conclude that in immunocompetent population it is not necessary to administer a booster dose 6.5 years after hepatitis B vaccination.