Inclusion Criteria:

• Subjects who the investigator believes that their parents/guardians can and will comply with the requirements of the protocol should be enrolled in the study.
• Subjects should have completed the full three-dose primary vaccination course in study 104567.
• A male or female child between, and including, 18 and 24 months of age at the time of the booster vaccination.
• Written informed consent obtained from the parent or guardian of the subject.
• Healthy subjects as established by medical history and clinical examination before entering into the study.

Exclusion Criteria:

• Use of any investigational or non-registered product (drug or vaccine) other than the study vaccine(s) within 30 days preceding booster vaccination, or planned use 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 booster dose.
• Administration of a vaccine not foreseen by the study protocol within 30 days prior to vaccination, or planned administration during the study period, with the exception of measles or combined measles, mumps and rubella (MMR) vaccination.
• 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.
• Previous booster vaccination against diphtheria, tetanus, pertussis and/or Haemophilus influenzae type b diseases since the end of the primary study.
• History of diphtheria, tetanus, pertussis and/or Haemophilus influenzae type b diseases.
• Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination.
• A family history of congenital or hereditary immunodeficiency.
• History of allergic disease or reactions likely to be exacerbated by any component of the vaccine(s).
• Major congenital defects or serious chronic illness.
• History of any progressive neurological disorders or seizures.
• Acute disease and/or fever at time of enrolment.
• Administration of immunoglobulins and/or any blood products within the three months preceding the booster dose or planned administration during the study period.

• Occurrence of any of the following adverse events (AEs) after previous administration of a DTP vaccine:

  • Hypersensitivity reaction due to any component of the vaccine.
  • Encephalopathy.
  • Fever >= 40.0 °C (axillary temperature) within 48 hours of vaccination.
  • Collapse or shock-like state within 48 hours of vaccination.
  • Persistent, inconsolable crying occurring within 48 hours of vaccination and lasting >= 3 hours.
  • Seizures with or without fever occurring within 3 days of vaccination.