Persistence of anti-HBs antibody and immune memory 18-19 years after vaccination against hepatitis B in Italy in two cohorts of individuals primed as infants or adolescents

Introduction: We assessed the anti-HBs persistence and immune memory 18-19 years after vaccination against hepatitis B in healthy individuals primed as infants or adolescents, respectively. Methods: Study population included 405 teenagers (Group A) vaccinated as infants, and 409 blood donors (Group B) vaccinated as adolescents. All vaccinees were tested for anti-HBs and anti-HBc; those found anti-HBc+ were further tested for HBsAg and HBV DNA. Individuals with anti-HBs concentration ≥10 mIU/ml were considered protected while those with anti-HBs concentration <10 mIU/ml were offered a booster dose and re-tested 2 weeks later. Results: Overall, 68.1% individuals showed anti-HBs concentrations ≥10 mIU/ml (48.9% in Group A vs 87% in Group B; p<0.001). The geometric mean concentration (GMC) was higher in Group B than in Group A (102.5 mIU/ml vs 6.9 mIU/ml; p<0.001). Eight individuals of Group B were positive for anti-HBc alone. When boosted, 93.7% of Group A and 94.7% of Group B showed an anamnestic response. Post-booster GMCs were similar in both groups (435.7 mIU/ml, Group A vs 710 mIU/ml, Group B, p=0.45). Conclusion: A strong immunological memory persists for at least 18-19 years after immunization of infants or adolescents with a primary course of vaccination. Booster doses are not needed.