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 who received the complete primary vaccination course according to his/her group allocation in the primary study
• Written informed consent obtained from the subject.

All subjects must satisfy the following criteria at entry into the challenge dose phase:

• A male or female who received the complete primary vaccination course according to his/her group allocation in the primary study.
• Subjects who participated in the long-term follow-up phase of the primary study and for whom the antibody concentrations were below specified value for anti-HAV antibodies and/ or for anti-HBs antibodies at the last available follow-up time-points.
• Subjects who the investigator believes that they can and will comply with the requirements of the protocol should be enrolled in the study.
• Written informed consent obtained from the subject.
• Healthy subjects as established by medical history and clinical examination before entering into the challenge dose phase of this study.
• If the subject is female, she must be of non-childbearing potential, i.e. either surgically sterilized; or, if of childbearing potential, she must be abstinent or have used adequate contraceptive precautions for 30 days prior to vaccination, have a negative pregnancy test and must agree to continue such precautions for two months after the vaccination.

Exclusion Criteria:

The following criteria should be checked at each follow-up visit. If any apply at study entry, the subject must not be included at that long-term follow-up visit.

• Use of any investigational or non-registered product (drug or vaccine) since the last blood sampling visit.
• Administration of a hepatitis A, hepatitis B or hepatitis combination vaccine since the primary vaccination course of the primary study.
• History of hepatitis A or hepatitis B infection.
• Administration of hepatitis A or hepatitis B immunoglobulins and/or any blood products within 3 months prior to blood sampling.

The following criteria should be checked before the challenge dose phase. If any apply, the subject must not be included in the challenge dose phase:

• Use of any investigational or non-registered product (drug or vaccine) within 30 days before the administration of the challenge dose or planned use during the study period outside the context of the study.
• Administration of a hepatitis A, hepatitis B or hepatitis combination vaccine between the primary vaccination course of the primary study and the challenge dose visit.
• History of hepatitis A or hepatitis B infection.
• Chronic administration (defined as more than 14 days) of immunosuppressants or other immune-modifying drugs within six months prior to the challenge dose.
• Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination (no laboratory testing required).
• History of allergic disease or reactions likely to be exacerbated by any component of the vaccines.
• Acute disease at the time of.
• Administration of immunoglobulins and/or any blood products within the three months preceding the administration of the challenge dose or planned administration before the final blood sampling point (one month after the challenge dose).
• Pregnant or lactating female.