Efficacy and immune memory of plasma-derived hepatitis B vaccine 11 years after primary immunization

OBJECTIVE: To evaluate the long-term efficacy of hepatitis B vaccine 10 years after primary immunization to provide scientific basis for the time of revaccination. METHODS: The study was strictly designed with randomization, double-blinding, and placebo-controlled method to observe the efficacy and immune memory 11 years following hepatitis B vaccination. RESULTS: Immunogenicity and protective rate of vaccine were still kept well 11 years after immunization with a protective rate against HBV infection of 73.5%. But, there was no significant difference in HBV infection rates between vaccine group and placebo-controlled group (7.89% vs. 13.25%, P > 0.1) nine to 11 years following immunization. There still existed immune memory 11 years after immunization, but it was significantly weaker than that within the first 10 years after immunization. CONCLUSION: The efficacy of the vaccine had begun to drop 11 years after immunization, which should be followed up further to reach a clear conclusion.