Six-year efficacy of hepatitis B revaccination: A double-blind, placebo- controlled and randomized field trial

In order to observe the efficacy of a booster dose of hepatitis B vaccine; 104 primary school children with a good response were enrolled in a double-bind, placebo-controlled and randomized field trial three years after the primary vaccination. At the end of the 6-year follow-up anti-HBs positive rate and GMT (of S/N value) in the revaccinated group were 54.5% and 12.0, still higher than those in the control group (40.5% and 4.8), but the difference of the positive rates was not statistically significant this time. Anti-HBs positive rate and GMT not only in the control group but in the revaccinated group had dramatically declined against those 3 years after the revaccination (the control group: 69.4% and 20.6; the revaccinated group: 87.8% and 43.3) (P < 0.01). The higher anti-HBs titer before the revaccination, the better the persistence of anti-HBs after the revaccination. HBV infection rate (calculated by person-year) in the revaccinated group was 1.44%, without statistical difference from 3.19% in the control group (P > 0.05) as before. Considering the perfect long-term efficacy of hepatitis B vaccine, we concluded that a booster dose 9 years after the primary immunization seems unnecessary.