This study aims to analyse the serologic response to PCV-1 in the PEDIARIX® [GSK Biologicals' Diphtheria and Tetanus Toxoids and Acellular Pertussis Adsorbed, Hepatitis B (Recombinant) and Inactivated Poliovirus Vaccine] and KINRIX® (GSK Biologicals' Diphtheria and Tetanus Toxoids and Acellular Pertussis Adsorbed and Inactivated Poliovirus Vaccine) vaccine products. The samples have been collected at pre-determined time points from a subset of subjects who participated in selected studies [217744/085 and 213503/048] conducted in the United States.

Serum samples from the previously conducted clinical trials (217744/085 and 213503/048) are used in this study.

Inclusion Criteria:

• Subjects enrolled previously in randomized, open and multicentre studies [217744/085; 213503/048].
• Subjects aged 6 months to 6 years at last dose vaccinated with either DTaP-HepB-IPV vaccine or separately administered DTaP, HepB, and IPV vaccines or DTaP-IPV vaccine or separately administered DTaP and IPV vaccines.
• Subjects for whom sufficient residual volume of the pre and post vaccination blood samples is available.

Exclusion Criteria:

• Not Applicable

Infants aged 2 and 6 months who were previously given a primary vaccination series consisting of a single dose of combination DTaP-HepB-IPV (PEDIARIX®) vaccine at 2, 4, and 6 months of age or separately administered DTaP (INFANRIX®), HepB (ENGERIX-B®), and IPV (Sanofi-Pasteur's IPOL) vaccines in the study 217744/085 and toddlers aged 4-6 years who were previously vaccinated with a single dose of either the combination DTaP-IPV (KINRIX®) vaccine or separately administered DTaP and IPV vaccines in the study 213503/048.