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.