Study to Compare Booster Vaccination With Pediacel® to Infanrix® Hexa When Both Are Co-Administered With Prevenar®

The purpose of the study is to provide data on the safety and immunogenicity of Pediacel® to allow its use as a fourth dose administered to 11-18 months old toddlers at the same time as Prevenar®. Primary Objective: To evaluate the safety of Pediacel® booster dose co-administered with Prevenar® to toddlers at 11-18 months of age. Secondary Objectives: * To describe the incidence rate of severe fever within four days post-vaccination * To describe the antibody responses to all antigens in a subgroup of subjects at baseline and post-vaccination.