An Open Single Centre Study to Evaluate the Long-term Antibody Persistence and Immune Memory Between 16 and 20 Years After the Primary Study HAB-028 (208127/021) in Which Healthy Adults Were Vaccinated With Twinrix Adult Following a Three-dose Schedule.

This study will evaluate the persistence of the immune response to HAV (Hepatitis A Virus) antigens and HBs (Hepatitis B surface) antigens in healthy adults previously vaccinated with GlaxoSmithKline (GSK) Biologicals' Twinrix™ Adult. The subjects will be invited for blood sampling 16, 17, 18, 19 and 20 years after vaccination to evaluate the antibody persistence. For subjects in whom low circulating antibodies are detected, the presence of immune memory against hepatitis A & B antigens will be investigated by the administration of a challenge dose of the appropriate vaccine (Havrix™ and/or Engerix™-B) at the next planned visit. No new subjects will be recruited during this study.