Evaluation of GlaxoSmithKline Biologicals' Boostrix® Vaccine in Comparison With Decavac™ Vaccine.

Inclusion Criteria: * Subjects who the investigator believes that can and will comply with the requirements of the protocol should be enrolled in the study. * Males or females 65 years of age and older at the time of study entry. * Free of an acute aggravation of the health status as established by medical history and medical history and clinical examination before entering into the study. * Written informed consent from all subjects. Exclusion Criteria: * Administration of a diphtheria-tetanus (Td) booster within the previous 5 years. * Administration of a Tdap vaccine at any time prior to study entry. * History of diphtheria and/or tetanus and/or pertussis disease. * Use of any investigational or non-registered drug or vaccine other than the study vaccines within 30 days preceding vaccination, or planned use during the entire study period. * Administration of other licensed vaccines within 2 weeks (for inactivated vaccines) or 4 weeks (for live vaccines) prior to enrolment in this study, with the exception of influenza, vaccine, which may be administered at any time up to or during the study period, including the day of study vaccination. * Planned administration of any vaccine not foreseen by the study protocol up to 30 days following vaccination, with the exception of influenza, vaccine, which may be administered at any time up to or during the study period, including the day of study vaccination. Pneumococcal and zoster vaccines can be administered at the discretion of the investigator when the subject comes back at Visit 2. * Chronic administration of immunosuppressants or other immune-modifying drugs within six months prior to vaccination or planned administration during the study period. * Any confirmed or suspected immunosuppressive or immunodeficient condition based on medical history and physical examination. * History of serious allergic reaction following any other tetanus toxoid, diphtheria toxoid or pertussis-containing vaccine or any component of the study vaccines. * History of encephalopathy within seven days of administration of a previous booster dose of pertussis vaccine that is not attributable to another identifiable cause. * Progressive neurologic disorder, uncontrolled epilepsy or progressive encephalopathy: pertussis vaccine should not be administered to individuals with these conditions until a treatment regimen has been established and the condition has stabilized. * Acute (active) clinically significant pulmonary, cardiovascular, hepatic or renal functional abnormality, as determined by clinical evaluation or pre-existing laboratory screening tests. * Acute disease at the time of vaccination. * Administration of immunoglobulins and/or any blood products within the three months preceding vaccination, or planned administration during the study period. * Any medical condition that, in the opinion of the investigator, might interfere with the evaluations required by the study.