Characterization of the serum antibody response induced by Haemophilus influenzae type b tetanus protein-conjugate vaccine in infants receiving a DTP-combined vaccine from 2 months of age

The serum antibody response induced by Haemophilus influenzae type b capsular polysaccharide (CPS)—tetanus protein conjugate vaccine combined to DTP vaccine was characterized in infants receiving three injections from 2 months of age. Sixty-five per cent and 94% of infants had anti-CPS antibody levels ⩾ 1 μg ml −1 after the second and third dose, respectively. The antibody response was mostly made up of IgG with marked IgG 1 predominance. Significant rises in bactericidal and in complement-mediated opsonic activities were observed after immunization. These data clearly show that this vaccine can be successfully administered in one syringe together with DTP vaccine during the regular infant immunization programme.