Assessment of GSK Biologicals' Tdap Candidate Vaccine Administered as a Booster (6th Dose) in Terms of Immunogenicity and Safety to Children and Adolescents Previously Vaccinated With Five Doses of an Acellular Pertussis-containing Vaccine.

Inclusion Criteria: \- Subjects previously enrolled and vaccinated in GSK Biologicals' studies APV-118 and APV-120 and who were 9 through 13 years of age Exclusion Criteria: * Use of any investigational or non-registered drug or vaccine other than the study vaccines within 30 days preceding the administration of study vaccines, or planned use during the study period. * Chronic administration or planned administration of immunosuppressants or other immune modifying drugs within six months prior to study vaccination or planned administration during the study period * Administration of immunoglobulins and/or blood products within 3 months prior to vaccination