The safety and immunogenicity of a booster dose of Hib-MenCY-TT vaccine will be compared to a booster dose of licensed Hib conjugate vaccine, each administered at 12 to 15 months of age. The group primed with the Hib conjugate vaccine will re-randomized at 12-15 months of age to receive a booster dose of Hib-MenCY-TT or a booster dose of the Hib conjugate vaccine.