• Anti-HAV antibody response to the challenge dose [ Time Frame: One month after the challenge dose. ] [ Designated as safety issue: No ]
• Anti-HBs antibody response to the challenge dose [ Time Frame: One month after the challenge dose ] [ Designated as safety issue: No ]

• Anti-HAV antibody response to the challenge dose [ Time Frame: One month after the challenge dose. ]
• Anti-HBs antibody response to the challenge dose [ Time Frame: One month after the challenge dose ]

• Occurrence, intensity and relationship to vaccination of unsolicited symptoms. [ Time Frame: 31-day follow-up period after challenge dose. ] [ Designated as safety issue: No ]
• Occurrence, intensity and relationship to vaccination of all SAEs following the administration of the challenge dose. [ Time Frame: Following the administration of the challenge dose. ] [ Designated as safety issue: No ]
• Anti-HAV and anti-HBs antibody concentrations at Month 48 [ Time Frame: At Month 48 after primary vaccination ] [ Designated as safety issue: No ]
• Anti-HAV antibody concentrations after the challenge dose [ Time Frame: Two weeks and one month after the challenge dose. ] [ Designated as safety issue: No ]
• Anti-HBs antibody concentrations after the challenge dose. [ Time Frame: Two weeks and one month after the challenge dose. ] [ Designated as safety issue: No ]
• Occurrence and intensity of solicited local symptoms. [ Time Frame: 4-day follow-up period after vaccination ] [ Designated as safety issue: No ]
• Occurrence, intensity and relationship of solicited general symptoms [ Time Frame: 4-day follow-up period after vaccination ] [ Designated as safety issue: No ]
• Retrospective recording of all serious adverse events (SAEs) with causal relationship to vaccination or referring to hepatitis A or B infection that occurred since the last study visit of the HAB-160 long-term follow-up study. [ Time Frame: since the last study visit of the HAB-160 long-term follow-up study. ] [ Designated as safety issue: No ]

• Anti-HAV and anti-HBs antibody concentrations at Month 48 [ Time Frame: At Month 48 after primary vaccination ]
• Anti-HAV antibody concentrations after the challenge dose [ Time Frame: Two weeks and one month after the challenge dose. ]
• Anti-HBs antibody concentrations after the challenge dose. [ Time Frame: Two weeks and one month after the challenge dose. ]
• Occurrence and intensity of solicited local symptoms. [ Time Frame: 4-day follow-up period after vaccination ]
• Occurrence, intensity and relationship of solicited general symptoms [ Time Frame: 4-day follow-up period after vaccination ]
• Retrospective recording of all serious adverse events (SAEs) with causal relationship to vaccination or referring to hepatitis A or B infection that occurred since the last study visit of the HAB-160 long-term follow-up study. [ Time Frame: since the last study visit of the HAB-160 long-term follow-up study. ]
• Occurrence, intensity and relationship to vaccination of unsolicited symptoms. [ Time Frame: 31-day follow-up period after challenge dose. ]
• Occurrence, intensity and relationship to vaccination of all SAEs following the administration of the challenge dose. [ Time Frame: Following the administration of the challenge dose. ]

Only subjects who participated in the primary study will be invited to participate in the extension phase and the challenge dose phase of this study.

• Hepatitis A
• Hepatitis B

• Biological: Twinrix
• Biological: Engerix-B
• Biological: Havrix
• Biological: HBVAXPRO
• Biological: Vaqta

Inclusion Criteria:

• Subjects who the investigator believes that they can and will comply with the requirements of the protocol.
• A male or female who completed the primary vaccination phase of the HAB-160 study.
• Written informed consent obtained from the subject.
• If the subject is female, she must be of non-childbearing potential; 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 the time of study entry. If any apply, the subject must not be included in the study:

• Use of any investigational or non-registered product (drug or vaccine) other than the study vaccines within 30 days preceding the challenge dose, or planned use during the study period.
• History of any hepatitis A or hepatitis B vaccination or infection since the primary vaccination study.
• History of allergic disease or reactions likely to be exacerbated by any component of the vaccine.
• Acute disease at the time of enrolment.
• Pregnant or lactating female.