Vaxcyte's 31-Valent Pneumococcal Vaccine Candidate Shows Promising Results

Phase 1/2 adult study data published in The Lancet Infectious Diseases highlight VAX-31's potential as a best-in-class pneumococcal conjugate vaccine

Mar. 18, 2026 at 11:34pm

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Vaxcyte, Inc. announced the publication of positive results from the VAX-31 adult Phase 1/2 clinical study in The Lancet Infectious Diseases. The study evaluated the safety, tolerability and immunogenicity of VAX-31, Vaxcyte's next-generation 31-valent pneumococcal conjugate vaccine (PCV) candidate, in healthy adults aged 50 and older. The results showed that VAX-31 was well-tolerated and demonstrated robust immune responses across all 31 serotypes, meeting or exceeding regulatory criteria. Based on these findings, Vaxcyte has advanced VAX-31 into a comprehensive Phase 3 adult program.

Why it matters

Pneumococcal disease is a serious public health concern, leading to significant morbidity and mortality, particularly in young children and older adults. Current PCVs have limitations in their serotype coverage, underscoring the need for broader-spectrum vaccines like VAX-31 that can provide protection against a wider range of pneumococcal strains.

The details

The VAX-31 Phase 1/2 study enrolled 1,015 healthy adults aged 50 and older and evaluated three dose levels of VAX-31 compared to the current standard-of-care PCV20. At all doses, VAX-31 demonstrated a safety profile similar to PCV20 and elicited robust opsonophagocytic activity (OPA) and immunoglobulin G (IgG) immune responses across all 31 serotypes. The VAX-31 High Dose, which is being evaluated in the ongoing Phase 3 program, met or exceeded the OPA response non-inferiority criteria for all 20 serotypes common with PCV20 and met the superiority criteria for the 11 incremental serotypes unique to VAX-31.

  • The VAX-31 Phase 1/2 clinical study was conducted in 2025.
  • The results from the study were published in The Lancet Infectious Diseases on March 18, 2026.
  • Based on the positive Phase 1/2 results, Vaxcyte advanced the VAX-31 High Dose into a comprehensive Phase 3 adult program.

The players

Vaxcyte, Inc.

A clinical-stage vaccine innovation company developing next-generation pneumococcal conjugate vaccines and other bacterial disease prevention candidates.

Grant Pickering

Chief Executive Officer and Co-Founder of Vaxcyte.

Jim Wassil

Executive Vice President and Chief Operating Officer of Vaxcyte.

Prevnar 20®

One of the current standard-of-care pneumococcal conjugate vaccines.

Capvaxive®

A 21-valent pneumococcal conjugate vaccine.

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What they’re saying

“The publication of these data, including both the OPA and IgG results, in The Lancet Infectious Diseases further affirms the potential of our site-specific, carrier-sparing platform to deliver the broadest-spectrum PCVs to provide protection against both currently circulating and historically prevalent serotypes.”

— Grant Pickering, Chief Executive Officer and Co-Founder of Vaxcyte

“These data directly informed the design of our comprehensive OPUS Phase 3 program, including the decision to advance the VAX-31 High Dose and the structure of our pivotal, noninferiority trial that includes head-to-head comparisons of VAX-31 to both PCV20 and Capvaxive®.”

— Jim Wassil, Executive Vice President and Chief Operating Officer of Vaxcyte

What’s next

Vaxcyte is currently evaluating the VAX-31 High Dose in the comprehensive OPUS Phase 3 adult clinical program, with topline data from the OPUS-1 pivotal noninferiority trial expected in the fourth quarter of 2026.

The takeaway

The positive Phase 1/2 results for Vaxcyte's 31-valent pneumococcal conjugate vaccine candidate, VAX-31, highlight its potential to set a new standard for adult pneumococcal vaccines by providing broader serotype coverage and robust immune responses compared to current standard-of-care options.