Vaxcyte's 31-Valent Pneumococcal Vaccine Candidate Meets Primary Endpoints in Phase 3 OPUS-1 Trial

Vaxcyte's investigational 31-valent pneumococcal conjugate vaccine (PCV) candidate VAX-31 met all prespecified primary endpoints compared with PCV20  (Prevnar 20, Pfizer) and/or PCV21 (Capvaxive, Merck) in the pivotal adult phase 3 OPUS-1 trial. The findings are topline results reported in a Vaxcyte announcement.

OPUS-1 is a randomized, double-blind, active-controlled trial in healthy, pneumococcal-naive US adults. Participants aged 50 years and older (n=3572) were randomized 1:1:1 to a single dose of VAX-31, PCV20, or PCV21. A separate cohort aged 18 to 49 years (n=475) was randomized 3:1 to VAX-31 or PCV20. Immune responses were assessed 1 month after vaccination.

In adults 50 and older, all 28 VAX-31 serotypes shared with PCV20 and/or PCV21 met the prespecified noninferiority criterion. That criterion was based on opsonophagocytic activity geometric mean ratios, with a lower bound of the 95% CI above 0.667. The 3 serotypes unique to VAX-31 and cross-reactive serotype 20B met the superiority criterion. VAX-31 also met the primary immunobridging endpoint in adults aged 18 to 49 compared with adults aged 50 to 64.

In comparisons with each vaccine individually, VAX-31 met the noninferiority criterion for 20 of 20 serotypes shared with PCV20 and 17 of 19 shared with PCV21. Against PCV21, serotypes 3 and 12F missed the 0.667 threshold but met a historical threshold of 0.5, which was a prespecified key secondary endpoint.

According to the company, VAX-31 was well tolerated and had a safety profile similar to PCV20 and PCV21. Solicited reactions were generally mild to moderate, and no serious adverse events were considered related to the study vaccines.

Vaxcyte expects results from the OPUS-2 and OPUS-3 trials in the first half of 2027. It plans to submit a biologics license application in the first half of 2028. VAX-31 holds FDA Breakthrough Therapy designation for prevention of invasive pneumococcal disease and pneumonia in adults.

Source: Vaxcyte, Inc. Vaxcyte reports positive topline data from OPUS-1, the pivotal adult phase 3 trial of VAX-31, the company's 31-valent pneumococcal conjugate vaccine candidate. Press release. Vaxcyte, Inc.; October 5, 2026. Accessed October 5, 2026.