The purposes of this study are to evaluate the safety of 13-valent pneumococcal Conjugate Vaccine (13vPnC) in children who have already been vaccinated with Prevenar. The study will also assess the immunological response (measure the amount of antibodies, i.e. proteins that fight off germs) produced by children after they have been given the 13-valent pneumococcal vaccine at 5 and 12 months or 12 months of age. In addition, reactions at the injection site will be assessed during the study.