Immunogenicity and safety of a DTaP-IPV//PRP~T vaccine (Pentaxim) booster dose during the second year of life in Indian children primed with the same vaccine.

Objective: To evaluate the immunogenicity and safety of a pentavalent (diphtheria, tetanus, acellular pertussis, inactivated poliovirus, Hib polysaccharide-conjugate) combination vaccine booster dose.

Design: Multicenter, open, Phase III clinical study.

Setting: Two tertiary-care hospitals in Delhi and Vellore, India.

Participants/patients: 207 healthy Indian children.

Intervention: The DTaP-IPV//PR~NT vaccine (Pentaxim) was given at 18-19 months of age to children who had been primed with the same vaccine at 6,10,14 weeks of age.

Main Outcome Measures: Immunogenicity was assessed before and 1 month after the booster. Safety was evaluated from parental reports, and investigator assessments.

Results: At 18-19 months of age, before boosting, the SP rates against diphtheria, tetanus, poliovirus and PRP were 82.3-100%; 90.0% of participants had anti-PRP >0.15 ug/mL. Anti-poliovirus titers were >1:8 dilution in 97.9-98.4% of participants. Anti-PT and FHA titers (5 EU/mL) were detectable in 82.5% and 90.8% of participants, respectively. One month after the booster dose, SP rates were 99.5% for PRP (>1.0 ug/mL), 100% for diphtheria, tetanus (>0.1 IU/mL) and polioviruses (>8:1/dilution). Sero-conversion (4 fold post-booster increase in anti-PT and -FHA concentration) occurred in 96.8% and 91.7%, respectively. Geometric mean concentrations (GMC) increased from 11.7 to 353.1 EU/mL and from 18.2 to 363.4 EU/mL for anti-PT and anti-FHA, respectively. Anti-PRP GMC increased from 1.75 to 70.5 ug/mL. Vaccine reactogenicity was low; severe solicited reactions were reported by <1.4% of participants.

Conclusion: The DTaP-IPV//PRP-T vaccine booster at 18-19 months of age was well tolerated and induced strong antibody responses.