This study is evaluating the safety and immunogenicity of Hib-MenCY-TT vaccine compared to control groups receiving licensed Hib or MenC conjugate vaccines, each administered at 2, 4, 6, and 12 to 15 months of age. Co-administration with live, attenuated measles, mumps, and rubella combination vaccine; and with live, attenuated varicella vaccine will be assessed with administration of the booster dose. The Protocol Posting has been updated in order to comply with the FDA Amendment Act, September 2007.