Vaxcyte, Inc. announced the completion of enrollment in its Phase 2 study evaluating VAX-24, a broad-spectrum, carrier-sparing 24-valent pneumococcal conjugate vaccine (PCV) candidate designed to prevent invasive pneumococcal disease (IPD), in healthy infants. Vaxcyte expects to announce topline safety, tolerability and immunogenicity data from the Phase 2 study primary three-dose immunization series by the end of the first quarter of 2025, followed by topline data from the booster dose by the end of 2025. The VAX-24 infant Phase 2 clinical study, which is now fully enrolled with 802 healthy infants, is a randomized, observer-blind, dose-finding two-stage clinical study evaluating the safety, tolerability and immunogenicity of VAX-24.

The Stage 1 portion of the study evaluated the safety and tolerability of a single injection of VAX-24 at three dose levels (low dose/1.1mcg, middle dose/2.2mcg, mixed dose/2.2mcg or 4.4mcg) and compared to VAXNEUVANCE (PCV15), which was the broadest-spectrum PCV at the time of study initiation, in 48 infants. The Stage 2 portion is evaluating the safety, tolerability and immunogenicity of VAX-24 at the same three dose levels and compared to Prevnar 20® (PCV20), currently the broadest-spectrum PCV recommended by the Advisory Committee on Immunization Practices (ACIP), in 754 infants. Participants who received VAX-24 in Stage 1 will continue the standard dosing regimen as part of Stage 2 and will be included in the safety, tolerability and immunogenicity analysis of the study. In line with recommendations from the ACIP, the study design includes a primary immunization series consisting of three doses given at two months, four months and six months of age, followed by a subsequent booster dose at 12-15 months of age, in conjunction with the other routinely recommended non-PCV vaccines on the infant immunization schedule.

The key prespecified immunogenicity study endpoints include an assessment of immune responses for all three VAX-24 doses and compared to PCV20 on the shared serotypes measured at 30 days post-dose three (PD3) and post-dose four (PD4). Immune responses will be assessed based on anti-pneumococcal polysaccharide serotype-specific immunoglobulin G (IgG) responses (proportion of participants achieving the accepted IgG threshold value of =0.35mcg/mL) at 30 days PD3 and IgG geometric mean titer ratios at 30 days PD4, among other immunogenicity endpoints. All participants in the study will be evaluated for safety through six months following the booster dose.

The study is being conducted at 32 sites in the United States.