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A combined DTPa-HBV-IPV/Hib vaccine containing diphtheria (D), tetanus (T), acellular pertussis (Pa), hepatitis B (HBV) and types 1, 2 and 3 inactivated polioviruses (IPV) extemporaneously mixed with a conjugated Haemophilus influenzae type b (Hib) vaccine (Group 1) was compared to the DTPa-HBV-IPV and Hib vaccines (Group 2) administered separately at 3, 5 and 11 months of age (n = 440). A microneutralization assay was used to detect antibodies against the 3 polio virus types (cut-off 1:8 dil), RIA for anti-HBs antibodies (cut-off 10 mIU/ml) and ELISA for antibodies against all other vaccine antigens (cut-off: 0.1 IU/ml for anti-tetanus and anti-diphtheria antibodies; 5 El.U/ml for antibodies against each of the 3 acellular pertussis antigens and 0.15 microg/ml for anti-PRP antibodies). Similar immune responses were observed in both groups 1 month after dose 2 as well as after dose 3. Six months after dose 2 however, the proportion of subjects maintaining an anti-tetanus antibody concentration > or = 0.1 IU/ml was lower in Group 2 and a slight group difference in favour of Group 1 was also observed for anti-PRP, anti-diphtheria and anti-polio type 1 antibody persistence prior to the third dose. The overall incidence of local and general solicited symptoms was similar in both groups. One subject discontinued study vaccination following an SAE considered to be related to vaccination. The DTPa-HBV-IPV/Hib combined vaccine is immunogenic and well tolerated when administered according to a 3, 5 and 11 month vaccination schedule and can therefore be considered as a feasible alternative to the separate administration of the pentavalent DTPa-HBV-IPV and the monovalent Hib vaccines.