Immunogenicity and safety of a liquid combination of DT-PRP-T vs lyophilized PRP-T reconstituted with DTP

The immunogenicity and safety of a combined diphtheria, tetanus, pertussis and Haemophilus influenzae type b-tetanus conjugate vaccine (DTP-PRP-T) was compared to the same combination obtained by the reconstitution of H. influenzae type b-tetanus conjugate vaccine lyophilized (PRP-T) with liquid diphteria-tetanus-pertussis vaccine (DTP). Two hundred and sixty-two healthy infants were randomized to receive a intramuscular injection of 0.5 ml of one of the above combination vaccines at 2, 4 and 6 months of age, and a subgroup of 134 infants received a booster dose at 12 months. Serum antibody levels to each vaccine component were measured at ages 2, 6, 7, 12 and 13 months. Systemic and local reactions were assessed during the first 3 days after each injection by diary cards distributed to the parents. After the third dose and booster administered at 12 months of age, significant equivalence between the groups was observed and the geometric mean titers of anti H. influenzae type b capsular polysaccharide (Hib-CP) antibodies were 5.9 and 32.6 μg ml^-1 for the liquid combination group and 5.8 and 19.4 for the lyophilized group, respectively. After the third dose, anti-Hib-PC antibody levels of ≤1.0 μg ml^-1 and 0.15 μg ml^-1 were seen in 94% and 100%, respectively, of the liquid combination group find 90 and 99%, respectively of the lyophilized group. After the booster nose, levels of ≤1.0 μg ml^-1 were observed in 100% and 93.5% of the liquid combination group and the lyophilized combination group, respectively. Systemic and local reactions to the vaccination were generally mild and did not differ significantly between the groups. We conclude that the liquid combination of DTP-PRP-T is safe and at least as immunogenic as the lyophilized preparation. This liquid preparation, like other combined vaccines may be helpful for planning vaccination programs with a reduced number of injections.