 This study will evaluate the immune response against Hepatitis-A HAV and Hepatitis B surface HBs antigen in healthy subjects aged 12 to 15 years at the time of primary vaccination, who received vaccination course with GSK Biologicals Twinrix Adult and Twinrix Junior vaccine, approximately 10 years ago in the primary study. The subjects will be invited for blood sampling at 11, 12, 13, 14 and 15 years after primary vaccination to evaluate the persistence of immune response. For subjects detected with decreased immunity, the presence of immune memory against hepatitis A B antigens will be investigated by the administration of a challenge dose of the appropriate vaccine 6 to 12 months after the Year 15 follow-up time-point. 