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

To evaluate the long-term efficacy of hepatitis B vaccine 10 years after primary immunization to provide scientific basis for the time of revaccination.

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.

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.

The efficacy of the vaccine had begun to drop 11 years after immunization, which should be followed up further to reach a clear conclusion.