The purpose of this observer blind study is to assess the safety in terms of fever >39°C (rectal temperature) and the immunogenicity in terms of antibody response following a booster vaccination with pneumococcal vaccine GSK 1024850A at 12 to 18 months of age in children previously primed with the same vaccines including a pneumococcal conjugate vaccine co-administered with a diphtheria, tetanus, whole cell pertussis (DTPw)-combined vaccine and OPV or IPV vaccines. Subjects participating in this study should have received three doses of pneumococcal conjugate vaccine in the primary study.