One-year post-primary antibody persistence and booster immune response to a DTaP-IPV//PRP~T vaccine (Pentaxim) given at 18 - 19 months of age in South African children primed at 6, 10 and 14 weeks of age with the same vaccine.

OBJECTIVE To assess the immunogenicity and safety of a pentavalent diphtheria, tetanus, acellular pertussis, inactivated poliovirus, Hib polysaccharide-conjugate vaccine booster. DESIGN, SETTING AND PARTICIPANTS A DTaP-IPV//PRP~T vaccine (Pentaxim, a Sanofi Pasteur AcXim family vaccine) was given to 182 healthy children in South Africa at 18 - 19 months of age following priming with the same vaccine plus a monovalent hepatitis B vaccine at 6, 10 and 14 weeks of age. Outcome measures. Seroprotection (SP) and seroconversion (SC) rates, geometric mean titres (GMTs) and concentrations (GMCs) were assessed before, and 1 month after, the booster dose. Safety was assessed using parental reports. RESULTS One month after primary vaccination, at least 94.3% of participants were seroprotected against tetanus (≥ 0.01 IU/ml), diphtheria (≥ 0.01 IU/ml), poliovirus (≥ 8 1/dil) and Haemophilus influenzae type b (Hib) infection (≥ 0.15 µg/ml). Before the booster dose, the SP rates ranged from 65.7% to 100%. One month after the booster dose, SP rates were 97.7% for Hib (anti-PRP titre 1.0 μg/ml), 100.0% for diphtheria (≥ 0.1 IU/ml) and 100% for tetanus (≥ 0.1 IU/ml) and poliovirus types 1, 2, 3 (≥ 8 1/dil). At least 95.7% of participants had 4 fold post-booster increases in anti-pertussis antibody titres. GMTs increased from 11.21 to 465.51 EU/ml and from 12.89 to 520.35 EU/ml for anti-PT and anti-FHA respectively. Anti-PRP GMT increased from 0.35 to 47.01 μg/ml. The DTaP-IPV//PRP~T vaccine booster was well tolerated, with fever ≥ 39.0°C in only 1.7% of participants. CONCLUSIONS Antibody persistence following priming was satisfactory. The pentavalent DTaP-IPV//PRP~T vaccine booster was highly immunogenic and well tolerated.