Vaxcyte’s investigational 31-valent pneumococcal conjugate vaccine, VAX-31, met all primary immunogenicity end points in the phase 3 OPUS-1 trial, demonstrating noninferiority to currently licensed vaccines across 28 shared serotypes in adults aged 50 years and older.
OPUS-1 Trial Results and Immunogenicity End Points
Researchers evaluated VAX-31 against comparator vaccines Prevnar 20 (PCV20) and Capvaxive (PCV21) in healthy, pneumococcal-naive US adults. In participants aged 50 years and older, the trial tested noninferiority—defined as a lower bound of the 95% confidence interval for opsonophagocytic activity geometric mean ratios above 0.667. VAX-31 met this threshold for all 11 serotypes shared across all 3 vaccines, the 9 shared only with PCV20, and the 8 shared only with PCV21.
In addition, the vaccine met superiority criteria—requiring a lower bound above 2.0—for the 3 serotypes unique to VAX-31 and cross-reactive serotype 20B. For adults aged 18 to 49 years, all 32 immunobridging comparisons against participants aged 50 to 64 years also met noninferiority.
VAX-31 matches comparator safety profiles across age groups
In prespecified individual comparisons, VAX-31 achieved noninferiority for 20 of 20 serotypes shared with PCV20 and 17 of 19 shared with PCV21. Serotypes 3 and 12F missed the 0.667 threshold against PCV21 but reached the historical threshold of 0.5. The overall safety profile of VAX-31 remained similar to PCV20 and PCV21 across all studied age groups. Solicited adverse reactions were generally mild to moderate and resolved within 48 hours, with no serious adverse events deemed vaccine-related.
Broader Clinical Program Timeline
The OPUS-1 study forms the clinical cornerstone for a planned Biologics License Application, which Vaxcyte aims to submit in the first half of 2028. Meanwhile, ongoing trials continue to evaluate the vaccine under different clinical conditions. The OPUS-2 trial is examining the co-administration of VAX-31 with seasonal influenza vaccines in 1,390 pneumococcal-naive adults. The OPUS-3 trial is assessing serotype-specific OPA responses in 752 adults who previously received licensed pneumococcal vaccines such as PPSV23 or PCV20. Vaxcyte expects topline results from both OPUS-2 and OPUS-3 in the first half of 2027.
Frequently Asked Questions About VAX-31
What is VAX-31?
VAX-31 is an investigational 31-valent pneumococcal conjugate vaccine designed by Vaxcyte to prevent invasive pneumococcal disease and pneumococcal pneumonia by covering 31 distinct serotypes plus serotype 20B.
How did VAX-31 perform against PCV21 for specific serotypes?
VAX-31 met noninferiority for 17 of 19 serotypes shared with PCV21. Serotypes 3 and 12F missed the 0.667 threshold against PCV21 but met the historical threshold of 0.5.
When will the OPUS-2 and OPUS-3 trial results be available?
Topline results from the OPUS-2 and OPUS-3 trials are expected in the first half of 2027.
What are the next regulatory steps for Vaxcyte?
Vaxcyte plans to submit a Biologics License Application for VAX-31 in the first half of 2028.
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