• Anti-hepatitis B surface antigen (HBs) antibody concentrations [ Time Frame: One month after the challenge dose of HBV vaccine ]
  

• Anti-HBs antibody concentrations [ Time Frame: Before and after challenge dose of HBV vaccine ]
  
• Occurrence of serious adverse events [ Time Frame: During the entire study period. ]
  

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.