Background: A 21-valent pneumococcal conjugate vaccine, PCV21, was developed to provide broader coverage against Streptococcus pneumoniae serotypes. PCV21 comprises 13 serotypes common to a licensed 13-valent pneumococcal conjugate vaccine (PCV13) and 8 additional serotypes. This study evaluated 3 PCV21 formulations with differences in antigen content for some serotypes, compared with PCV13, administered concomitantly with routine pediatric vaccines. Methods: This was a randomized, modified double-blind, multicenter, active-controlled phase 2 study enrolling toddlers previously vaccinated with 3 doses of PCV13 (cohort 1) and unvaccinated infants (cohort 2). Toddlers/infants were randomized 1:1:1:1 to 1 of 3 PCV21 formulations or PCV13, administered at ages 12–15 months (cohort 1) and 2, 4, 6 and 12–15 months (cohort 2). Safety was assessed throughout the study. Immunogenicity was assessed 30 days after dose 1 (cohort 1) or doses 3 and 4 (cohort 2). Results: Overall, 140 toddlers (cohort 1) and 712 infants (cohort 2) were randomized. All PCV21 formulations showed acceptable safety profiles comparable with PCV13. In both cohorts, serotype-specific immunoglobulin G concentrations showed that PCV21 elicited a robust immune response for all serotypes. PCV21 and PCV13 showed generally comparable immunogenicity for shared serotypes, with numerically greater immunogenicity in the PCV21 groups than in the PCV13 group for the additional serotypes. Increased antigen content for selected serotypes appeared to be associated with greater immunogenicity. Conclusion: PCV21 demonstrated favorable immunogenicity, with no safety concerns identified. This study supports the evaluation of the PCV21 formulation that had the highest antigen content for selected serotypes for phase 3 assessment.
Pichon et al. (Fri,) studied this question.