Immune memory response induced in vitro by recombinant hepatitis B surface antigen challenge 13-18 years after primary vaccination.

The question of whether booster doses are required to maintain long-term protection against hepatitis B virus (HBV) after primary vaccination remains to be determined. Thus, the aim of this study was to evaluate the immune memory responses to hepatitis B surface antigen (HBsAg) challenge in vaccinated individuals through an in vitro-specific stimulation assay. Peripheral blood mononuclear cells (4 × 10(6)  cells/ml) were stimulated with 50 ng/ml of recombinant HBsAg. In vitro anamnestic antibody responses, as shown by detection of high avidity antibody in culture supernatants, were found 13-18 years after primary vaccination and were not correlated with serum antibodies (r = -0.177; P = 0.377). In addition, the findings from this study indicate that immune memory against hepatitis B was well preserved in 40.0% and 60.0% of vaccinees with anti-HBs levels less than 10 IU/L or lacking serum antibodies altogether, respectively. In conclusion, the data suggest the presence of immunological memory in vaccinated individuals, including those who showed anti-HBs <10 IU/L or undetectable antibody.