This study will be conducted in two stages. In the diphtheria, tetanus, pertussis (DTP) booster phase, subjects will receive a booster dose of Tritanrix™-HepB/Hib-MenAC or Tritanrix™-HepB/Hiberix™ (active control) at 15 to 18 or 24 months in a single-blind manner so that the subjects' parents will not know which vaccine was administered to their child. In the Mencevax ACWY phase at 24-30 months, a dose of Mencevax™ ACWY will be given in an open manner to only those subjects who received less than 4 doses of Tritanrix™-HepB/Hib-MenAC. No blood samples will be taken in this safety study.