Immunogenicity and safety of a novel combined Haemophilus influenzae type b-Neisseria meningitidis serogroups C and Y-tetanus-toxoid conjugate vaccine (Hib-MenCY-TT) candidate was evaluated when co-administered with DTPa-HBV-IPV(Pediarix(TM3)) + PCV7(Prevnar(TM4)) at 2-4-6 months of age. Anti-PRP concentrations >= 1.0 mu g/mL were observed in 92.9-98.7%, rSBA-MenC/Y titres >= 1:8 in >98%, rSBA-MenC/Y titres >= 1:128 in >95.8 and >89.9% subjects. PRP and MenC responses were similar to respective controls (ActHIB(TM5) and Menjugate(TM6)) including for antibody persistence. Response to co-administered vaccines was not impaired. Polysaccharide challenge (PRP, PSC, PSY at 11-14 months of age) evidenced immune memory was induced for Hib, MenC/Y conjugate components. The safety profile of Hib-MenCY-TT was similar to controls. Hib-MenCY-TT administered according to the current US Hib vaccine schedule has the potential to induce protective antibodies against Hib and meningococcal-CY disease in infants and toddlers. (c) 2007 Elsevier Ltd. All rights reserved.