Vaxcyte, Inc. announced that the first participants were dosed in the Phase 1/2 clinical study of VAX-24. This clinical proof-of-concept study will evaluate the safety, tolerability and immunogenicity of VAX-24, a 24-valent pneumococcal conjugate vaccine (PCV) candidate designed to prevent invasive pneumococcal disease (IPD) and pneumonia in adults. The Company expects to announce topline safety, tolerability and immunogenicity results from the Phase 1/2 study by the end of 2022.

The VAX-24 Phase 1/2 clinical proof-of-concept study is a randomized, observer-blind, dose-finding, controlled study designed to evaluate the safety, tolerability and immunogenicity of VAX-24 in healthy adults. The Phase 1 portion of the study will evaluate the safety and tolerability of a single injection of VAX-24 at three dose levels and compared to Prevnar 20™ in approximately 64 healthy adults 18 to 49 years of age. The Phase 2 portion will evaluate the safety, tolerability and immunogenicity of a single injection of VAX-24 at three dose levels and compared to Prevnar 20™ in approximately 800 healthy adults 50 to 64 years of age.

The prespecified immunogenicity endpoints of the Phase 2 portion of the study include an assessment of the induction of antibody responses, using immunoglobulin G (IgG) and opsonophagocytic activity (OPA), at each of the three VAX-24 doses and compared to Prevnar 20™ and, for the additional four serotypes contained in VAX-24 and Pneumovax® 23 but not in Prevnar 20™, the four-fold rise in antibody titers. The study will be conducted at approximately 13 sites in the United States.