Vaxcyte's VAX-31 Meets Phase 3 Goals Against Prevnar 20 and Capvaxive; Shares Nearly Double Premarket

Vaxcyte said on October 5 that VAX-31, its 31-valent pneumococcal conjugate vaccine, met its goals in OPUS-1, the pivotal adult Phase 3 trial whose topline results the company had scheduled for an 8:00 a.m. ET webcast. The study enrolled 4,047 pneumococcal-naive U.S. adults. In adults 50 and older (n=3,572), VAX-31 was compared head to head with PFE's Prevnar 20 (PCV20) and MRK's Capvaxive (PCV21) on immune response one month after a single dose, according to the company's release.

All 28 serotypes VAX-31 shares with PCV20 and/or PCV21 met the non-inferiority bar, and the three serotypes unique to VAX-31 plus cross-reactive 20B met superiority. Against Prevnar 20 the result was clean, 20 of 20 shared serotypes. Against Capvaxive it was 17 of 19: serotypes 3 and 12F missed the main 0.667 threshold and met only a historical lower bound of 0.5. Reactions were mild to moderate and resolved within 48 hours, with no vaccine-related serious adverse events. The endpoint is immunogenicity, a surrogate, not a measure of disease prevented.

PCVX shares rose 91% in premarket trading from Friday's $56.48 close, per Reuters, as the readout removed the main binary risk on the company's lead program. The broader serotype coverage targets a pneumococcal vaccine market dominated by Pfizer. What to watch: OPUS-2 and OPUS-3 data in the first half of 2027, a planned biologics license application in the first half of 2028, and how regulators and vaccine advisers weigh the two serotypes where VAX-31 trailed Capvaxive's bar.