Positive VAX-31 Phase 1/2 Adult Data Published in The Lancet Infectious Diseases Highlight Best-in-Class Potential of Vaxcyte’s 31-Valent Pneumococcal Conjugate Vaccine (PCV) Candidate

Based on the Strength of Unprecedented Results from the Positive Phase 1/2 Study in Adults Aged 50 and Older, Vaxcyte Advanced VAX-31 High Dose into Comprehensive Phase 3 Adult Program; Topline Data from the OPUS-1 Pivotal Noninferiority Trial Expected in the Fourth Quarter of 2026

At All Doses Studied, VAX-31 Demonstrated Robust Opsonophagocytic Activity and Immunoglobulin G Immune Responses for All 31 Serotypes and Was Observed to be Well Tolerated with a Safety Profile Similar to Prevnar 20®

Results Further Validate Potential of Vaxcyte’s Carrier-Sparing Platform to Deliver Broadest-Spectrum PCV Candidates that Provide Protection Against Both Currently Circulating and Historically Prevalent Serotypes

VAX-31 is Designed to Cover ~95% of Invasive Pneumococcal Disease (IPD) and ~88% of Pneumococcal Pneumonia in U.S. Adults Aged 50 and Older, with Potential to Provide an Incremental 14-34% Broader IPD Coverage and 19-31% Broader Pneumonia Coverage than Standard-of-Care Vaccines

Excerpt from the Press Release:

SAN CARLOS, Calif., March 18, 2026 (GLOBE NEWSWIRE) — Vaxcyte, Inc. (Nasdaq: PCVX), a clinical-stage vaccine innovation company, today announced the publication of results from the positive VAX-31 adult Phase 1/2 clinical study in the journal The Lancet Infectious Diseases. The study evaluated the safety, tolerability and immunogenicity of VAX-31, the Company’s next-generation 31-valent pneumococcal conjugate vaccine (PCV) candidate, for the prevention of invasive pneumococcal disease (IPD) and pneumonia compared to one of the current standard-of-care vaccines, Prevnar 20® (PCV20), in healthy adults aged 50 years and older. Based on the positive results of this Phase 1/2 study, VAX-31 is currently being evaluated in the OPUS Phase 3 adult program.

The study results showed that VAX-31 was observed to be well tolerated and demonstrated a safety profile similar to PCV20 through the full six-month evaluation period at all doses studied. At all doses studied, VAX-31 demonstrated robust opsonophagocytic activity (OPA) and immunoglobulin G (IgG) immune responses, with high geometric mean concentrations (GMCs) across all 31 serotypes. The VAX-31 High Dose, which is currently being evaluated in the OPUS Phase 3 program, met or exceeded the OPA response non-inferiority criteria¹ for all 20 serotypes common with PCV20 and met the superiority criteria² for the 11 incremental serotypes unique to VAX-31 and not in PCV20. The VAX-31 High Dose average OPA immune responses were greater for 18 of 20 serotypes compared to PCV20 (geometric mean ratio (GMR) greater than 1.0), with seven of these serotypes achieving statistically higher immune responses³ compared to PCV20.

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