Immune Response to Hepatitis B Vaccine Challenge Dose in Subjects Who Received a Primary Neonatal Hepatitis B Vaccine.

Inclusion Criteria: * Subjects who the investigator believes that they can and will comply with the requirements of the protocol should be enrolled in the study. * A male or female adult who received the complete neonatal primary vaccination course of hepatitis B vaccine in primary study approximately 20 years earlier. * Documented level of anti-HBs antibody concentrations \< specified concentration at the previous long-term time point for which serological results are available for that subject. * Written informed consent obtained from the subject. * Healthy subjects as established by medical history and clinical examination before entering into the study. * If the subject is female, she must be of non-childbearing potential or if she is of childbearing potential, she must practice adequate contraception for 30 days prior to vaccination, have a negative pregnancy test and continue such precautions for 2 months after completion of the hepatitis B challenge dose. Exclusion Criteria: * Chronic administration (defined as more than 14 days) of immunosuppressants or other immune-modifying drugs within six months prior to the hepatitis B vaccine challenge dose. * Administration of a vaccine not foreseen by the study protocol during the study period. * Administration of immunoglobulins and/or any blood products during the study period. * Drug and/or alcohol abuse.