Evaluation of Antibody Persistence & Immune Memory in Subjects Vaccinated During Adolescence With Twinrix™

Blood sampling at Years 11, 12, 13, 14, 15 and at the time of challenge dose administration and one month after challenge dose administration.

If a subject became seronegative for anti-HAV antibodies (\< 15 mIU/mL) or if anti-HBs antibody concentrations decreased below 10 mIU/mL during the long-term follow-up, immune memory against the antigen was evaluated by administering a challenge dose of the appropriate antigen (vaccine) 6 to 12 months after the Year 15 follow-up time-point.