Vaxcyte, Inc. announced the publication of the results from the VAX-24 Phase 1/2 clinical proof-of-concept study in the journal The Lancet Infectious Diseases. This study evaluated the safety, tolerability and immunogenicity of Vaxcyte?s investigational 24-valent, carrier-sparing pneumococcal conjugate vaccine (PCV) compared to the current standard-of-care, Prevnar 20® (PCV20), for the prevention of invasive pneumococcal disease (IPD) in healthy adults 18-64 years of age. The study results showed VAX-24 demonstrated a safety and tolerability profile that was comparable to PCV20 at all doses studied, and an immunogenicity profile that met or exceeded established regulatory immunogenicity standards for all 24 serotypes at the conventional 2.2 mcg dose.

The Company plans to advance the VAX-24 2.2 mcg dose into a Phase 3 program. The VAX-24 Phase 1/2 clinical proof-of-concept study was a randomized, observer-blind, dose-finding, controlled study designed to evaluate the safety, tolerability and immunogenicity of VAX-24 in healthy adults 18-64 years of age. Safety and Tolerability Findings: Through six months, VAX-24 demonstrated safety and tolerability results similar to PCV20 across all ages and doses studied.

Frequently reported local and systemic reactions were generally mild-to-moderate, resolving within several days of vaccination, with no meaningful difference observed across the cohorts. There were no serious adverse events or new onset chronic illnesses reported that were considered to be related to study vaccines. Immunogenicity Findings: VAX-24 demonstrated robust opsonophagocytic activity (OPA) and immunoglobulin G (IgG) immune responses for all 24 serotypes at all doses studied (1.1 mcg, 2.2 mcg, 2.2 mcg/4.4 mcg).

The VAX-24 2.2 mcg dose met or exceeded the established regulatory immunogenicity standards for all 24 serotypes and is the dose the Company plans to advance into a Phase 3 clinical program beginning with the pivotal, non-inferiority study for which the Company expects topline safety, tolerability and immunogenicity data in 2025. At the 2.2 mcg dose, VAX-24 met the standard OPA response non-inferiority criteria(1) for all 20 serotypes common with PCV20, of which 16 serotypes (3, 4, 6B, 7F, 8, 9V, 10A, 11A, 12F, 14, 15B, 18C, 19A, 19F, 23F and 33F) achieved higher immune responses and four serotypes (9V, 18C, 19F and 33F) reached statistical significance. At all three doses, VAX-24 met the standard superiority criteria(2) for all four serotypes (2, 9N, 17F and 20B) unique to VAX-24.

The VAX-24 Phase 1/2 clinical proof-of-concept study was conducted in two stages. The Phase 1 portion of the study evaluated the safety and tolerability of a single injection of VAX-24 at three dose levels, 1.1 mcg, 2.2 mcg and 2.2 mcg/4.4 mcg, and compared to PCV20 in 64 healthy adults 18 to 49 years of age. The Phase 2 portion evaluated the safety, tolerability and immunogenicity of a single injection of VAX-24 at the same three dose levels and compared to a single injection of PCV20 in 771 healthy adults 50 to 64 years of age.

The immunogenicity objectives of the Phase 2 portion of the study included an assessment of the induction of antibody responses, using OPA and IgG, at each of the three VAX-24 doses and compared to PCV20 and, for the additional four serotypes contained in VAX-24 (and Pneumovax® 23), but not in PCV20, the percentage of subjects that experienced a four-fold rise in antibody titers. Participants in the study were evaluated for safety through six months after vaccination.