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This study assessed the persistence of antibodies following primary vaccination with two commercially available, hexavalent diphtheria, tetanus, acellular pertussis, hepatitis B, inactivated poliovirus and Haemophilus influenzae type b vaccines (Infanrix hexa and Hexavac). The immunogenicity and reactogenicity of booster vaccination with Infanrix hexa were also evaluated. A total of 329 children primed at 2, 4, and 6 months with Infanrix hexa (n=166) or Hexavac (n=163) received booster vaccination with Infanrix hexa at 12-19 months of age. Antibody concentrations were measured immediately before and 1 month after booster vaccination. Prebooster persistence of antibodies to HBs, PRP and poliovirus types was significantly higher in children primed with Infanrix hexa than with Hexavac, both in terms of seroprotection rate and GMCs/GMTs (p < 0.05). Boosting with Infanrix hexa elicited strong immune responses to all antigens irrespective of the primary vaccine used, with post-booster seroprotection rates comparable between the two primary vaccine groups (ranging from 98.1 to 100%). The incidence of clinically relevant solicited symptoms did not differ significantly between primary vaccine groups, even if the incidence of local symptoms appeared to be more frequent in subjects primed with Infanrix hexa than in those primed with Hexavac. In summary, booster vaccination with Infanrix hexa during the second year of life is immunogenic and well tolerated, offering protection irrespective of the primary combination vaccine used.