Persistence of Hepatitis B Antibody Levels & Immune Response to a Hepatitis B Vaccine Challenge

Inclusion Criteria: * Subjects who the investigator believes that their parents/guardians can and will comply with the requirements of the protocol * A male or female of 4 to 5 years of age at the time of enrolment. * With documented evidence of previous vaccination with four consecutive doses of Infanrix hexa™ in Germany. * Written informed consent obtained from the parents or guardians of the subject at the time of enrolment. * Healthy subjects as established by medical history and clinical examination before entering into the study. Exclusion Criteria: * Concurrently participating in another clinical study, at any time during the study period, in which the subject has been or will be exposed to an investigational or a non-investigational product . * Evidence of previous hepatitis B booster vaccination since administration of the fourth dose of Infanrix hexa™ booster in the second year of life. * History of or intercurrent hepatitis B disease. * Hepatitis B vaccination at birth. * Planned administration/administration of a vaccine not foreseen by the study protocol during the period starting from 30 days before booster vaccination and ending 30 days after. * Administration of immunoglobulins and/or any blood products within the three months preceding booster vaccination or planned administration during the study period. * Chronic administration (defined as more than 14 days) of immunosuppressants or other immune-modifying drugs within six months prior to the HBV vaccine challenge.