Comparison of long-term (10 years) immunogenicity of two- and three-dose regimens of a combined hepatitis A and B vaccine in adolescents.

300 adolescents aged 12–15 years were randomised (1:1) into two groups to compare the long-term (10 years) immunogenicity profile of two doses of an Adult formulation [Group HAB_2D: 150; 0–6 months] vs. three doses of a Paediatric formulation [Group HAB_3D: 150; 0–1–6 months] of a combined hepatitis A and B (HAB) vaccine. At Year 10, anti-HAV seropositivity rate was 100% in both groups, while 85.9% and 85.1% subjects in the HAB_2D and HAB_3D groups, respectively, had anti-HBs antibody concentrations ≥10mIU/mL. The anti-HAV antibody GMCs (HAB_2D: 429.3mIU/mL; HAB_3D: 335.5mIU/mL) and anti-HBs antibody GMCs (HAB_2D: 50.6mIU/mL; HAB_3D: 60.1mIU/mL) were similar in both groups. No vaccine-related serious adverse events were reported. Hence, with respect to long-term antibody persistence, the two-dose schedule of the combined HAB vaccine Adult formulation is an effective alternative to the conventional three-dose schedule of the Paediatric formulation in adolescents.