Safety and Immunogenicity Study of Hib-MenCY-TT Vaccine Compared to Licensed Hib Conjugate Vaccine

The subjects from this study will participate in one of three cohorts: * US Safety and Immunogenicity (Cohort 1): All immunogenicity analyses in the primary and booster phases will be evaluated in this cohort. These subjects will also contribute to the safety analyses in the primary and booster phases. * Safety Only (Cohort 2): Only safety objectives will be assessed in the primary and booster phases for this cohort. * Non-US Safety and Immunogenicity (Cohort 3): Only descriptive immunogenicity results in the primary and booster phases will be reported for this cohort. These subjects will also contribute to the safety analyses in the primary and booster phases. Treatment allocation: Primary phase: Subjects will be randomized with balanced allocation (1:1:1:1) to 1 of the 4 treatment groups and with a stratification according to the cohort. Assignment to a cohort will be based on study site. Booster phase: Subjects who received Hib-MenCY-TT vaccine in the primary phase will receive a booster dose of Hib-MenCY-TT vaccine. Subjects who received ActHIB in the primary phase will receive a booster dose of PedvaxHIB. During the 3-dose primary vaccination course, co-administration of Prevnar, Synagis, and/or rotavirus vaccine is permitted; co-administration of influenza vaccine is permitted at dose 3. During the booster vaccination, co-administration of Prevnar, hepatitis A vaccine and influenza vaccine is permitted for all subjects in Cohort 1, 2 and 3; and co-administration of measles, mumps, rubella and varicella vaccine is permitted for all subjects in Cohort 2 and 3. The study will be conducted in a double-blind fashion with regard to consistency of the 3 manufacturing lots of Hib-MenCY-TT vaccine and single-blind fashion for Hib-MenCY-TT vaccine versus monovalent Hib vaccine. The parents/guardians will be blinded up to collection of all data pertaining to the period up to one month after booster vaccination. Therefore, the extended safety follow-up after the booster dose will be conducted in an unblinded manner. The person administering the vaccines will ensure that the parent/guardian does not see the vaccine vial used in reconstituting the vaccine. Due to the differences in the presentations of the candidate Hib-MenCY-TT vaccine and control vaccines, it is not possible to blind study personnel who administer the vaccines.