Lot-to-Lot Consistency of a Combined Hexavalent Diptheria-Tetanus-Acellular-Pertussis, Hepatitis B, Inactivated Polio and Haemophilus b Conjugate Vaccine, Administered to Healthy Chilean Infants at Two, Four and Six Months of Age

Objectives: To assess the safety, immunogenicity and lot consistency of a liquid hexavalent combined vaccine (DTaP-IPV-PRP similar to T-HBs, HEXAVAC (R)) (Sanofi-Pasteur MSD, France) administered to infants at two, four and six months of age. Methods: A total of 1028 infants were vaccinated with one of three vaccine lots, in a randomized, double-blind fashion. Equivalence testing was used to compare post-vaccination seroprotection/seroconversion rates and geometric mean titers (GMTs) for each antigen between the three lots. Blood samples were drawn before vaccination and one month after the third dose. Local and systemic adverse events were monitored for three days following each injection. Results: Equivalence between lots was demonstrated for all antigens, on post-dose 3 seroprotection/seroconversion rates and GMTs. Reported rates of local and systemic adverse events tended to increase with subsequent doses. Altogether, 11.8% of the infants reported at least one adverse local event (mainly redness and induration/swelling) after the first dose and 36.1% after the third dose. Systemic adverse events (mainly irritability and fever) were reported by 39.2% of the infants after the first dose and by 57.5% after the third one. Conclusion: Three separate lots of the liquid hexavalent combined vaccine induced consistently protective antibody responses against all antigens. These results and the well established clinical tolerability of this combined vaccine make it suitable for primary immunization of infants at two, four and six months of age.