Study to Evaluate the Immune Response of Healthy Subjects Who Received Neonatal Vaccination Course With GSK Biologicals' Engerix™-B Vaccine, Approximately 20 Years Ago.

This study will evaluate the immune response of healthy subjects who received neonatal vaccination course with GSK Biologicals' Engerix™-B vaccine, approximately 20 years ago. The presence of immune memory against hepatitis B surface antigen (HBsAg) in these subjects will be investigated by the administration of a challenge dose of hepatitis B vaccine and the comparison of their antibody concentration before and one month after vaccination. This protocol posting deals with objectives & outcome measures of the booster phase. No new subjects will be recruited during this booster phase of the study.