Humoral and cellular immune responses to a hepatitis B vaccine booster 15-18 years after neonatal immunization

Background. Whether hepatitis B (HB) vaccine-conferred immunity persists into adulthood is unknown. We aimed to investigate long-term HB immunity in adolescents. Methods. In 2004-2005, 6156 high school students (15-21 years old) who had been vaccinated with plasma-derived HB vaccine as infants were recruited for HB seromarker screening. The immune response to an HB vaccine booster was evaluated in 872 subjects who were seronegative. HB surface antibody (anti-HBs) titers and levels of HB surface antigen (HBsAg)-specific interferon (IFN)-gamma- or interleukin (IL)-5-secreting peripheral blood mononuclear cells (PBMCs; measured by enzyme-linked immunospot assay) were determined 4 weeks later. Results. Although the vaccine remained highly efficacious in reducing the HBsAg positivity rate, 63.0% of the vaccinees had no protective anti-HBs. After the booster, anti-HBs remained undetectable in 28.7% (158/551) of the subjects who had received complete HB vaccination (4 doses) during infancy. We estimated that 10.1% of the total population had lost their HB vaccine-conferred booster response. HBsAg-specific IFN-gamma- or IL-5-secreting PBMCs remained negative in 27.2% (25/92) of subjects after the booster. Conclusions. A notable proportion of fully vaccinated adolescents had lost immune memory conferred by a plasma-derived HB vaccine 15-18 years later. This decay of immune memory may raise concerns about the need for a booster vaccine for high-risk groups in the long run.