Immunogenicity of a combined DTPa-HB vaccine co-administered with Haemophilus influenzae type B conjugate vaccine (PRP-T) for primary and booster vaccinations.

OBJECTIVE To evaluate the immunogenicity of a combined DTPa-HB vaccine co-administered with Haemophilus influenzae type b conjugate vaccine (PRP-T) in Brazilian infants. MATERIAL AND METHODS A prospective and open clinical study, in which 110 infants were immunized with a three-dose primary vaccination regime at two, four and six months of age and with a single booster vaccination. Blood samples were drawn immediately before the first dose, one month after the third dose, at the time of the booster dose and one month after the booster to assess seropositivity and antibody geometric mean titers (GMTs) of antibodies for diphtheria, tetanus, hepatitis B, Haemophilus influenzae type b and for the three pertussis antigens: Pertussis Toxin (PT), Filamentous Hemagglutinin (FHA) and Pertactin (PRN). RESULTS Among the original 110 infants, 93 completed the study. Seropositivity was 100% for all seven involved antibodies, after the primary vaccination course. At the time of the booster dose, all antibodies (except diphtheria 33.7% and anti-PT 59%) were seropositive for more than 94% of subjects. After the booster, seropositivity increased to 100% for all antibodies. The GMT of these antibodies followed a similar pattern, with a strong increase after the primary course, followed by a second increase after the booster dose. At this time, GMT was 2- to 7-fold higher than after the primary course, for all vaccine components. CONCLUSIONS Concomitant administration of DTPa-HB and Hib vaccines elicited strong seroprotection for all the antigenic components. No interference with antibody response was evident. The vaccines provided high immunogenicity, following both the primary vaccinations and the booster dose.