Vaxcyte Surges 50% as VAX-31 Wins Phase 3 Trial

Vaxcyte (PCVX) shares jumped about 50% after VAX-31 met every primary endpoint in a pivotal Phase 3 trial against Pfizer's Prevnar 20 and Merck's Capvaxive.

Lead

What Did the OPUS-1 Trial Show?

OPUS-1 showed that VAX-31 matched the immune response of both incumbent vaccines and beat them on the serotypes they do not cover. The randomized, double-blind study enrolled 4,047 participants at about 30 U.S. sites. Of those, 3,572 were pneumococcal-naive adults aged 50 and older, randomized 1:1:1 to VAX-31, Prevnar 20 or Capvaxive. Another 475 adults aged 18 to 49 were randomized 3:1 to VAX-31 or Prevnar 20.

In adults 50 and older, all 28 VAX-31 serotypes shared with the two comparators met the noninferiority threshold, a lower confidence bound above 0.667. The three serotypes unique to VAX-31, plus cross-reactive serotype 20B, met the stricter superiority criterion of a lower bound above 2.0. In younger adults, VAX-31 met noninferiority on all 32 serotype comparisons against the 50 to 64 age group.

The head-to-head results carried one nuance. Against Prevnar 20, all 20 shared serotypes cleared noninferiority. Against Capvaxive, 17 of 19 shared serotypes did so, while serotypes 3 and 12F met a historical bar of 0.5 instead. Safety was in line with the comparators. Reactions were mild to moderate and mostly resolved within 48 hours. No serious adverse events were tied to the vaccines, and no participant left the study over side effects.

How Did Vaxcyte Shares React?

Vaxcyte shares rose sharply and hit a new 52-week high, with intraday gains reported between about 30% and 50%. The move came on a company with roughly $2.5 billion in cash and investments at June 30, 2026, against a second-quarter net loss of $284.3 million. The cash balance funds the remaining Phase 3 program and manufacturing scale-up.

Why Does This Matter for Pfizer and Merck?

The result matters because it is the first pivotal evidence that a higher-valency shot can match the current market leaders while adding coverage. Prevnar 20 is the entrenched adult pneumococcal franchise for Pfizer. Capvaxive, a 21-valent vaccine, is Merck's newer entrant built around the serotypes driving adult disease. VAX-31 targets both groups of serotypes, those currently circulating and those historically important, in a single injection.

Vaxcyte's platform is described as carrier-sparing. It uses fewer carrier proteins per dose, which the company argues lets it add serotypes without weakening the immune response to each. OPUS-1 is the first large human validation of that approach in adults. The comparison against Capvaxive on serotypes 3 and 12F will draw scrutiny in regulatory and commercial discussions.

What Comes Next for VAX-31?

The next catalysts are two more adult Phase 3 readouts and an infant data set. OPUS-2 and OPUS-3 results are expected in the first half of 2027. Phase 2 infant data, covering both the primary series and the booster dose, are due by the end of that period. Together with a manufacturing consistency study, those readouts are meant to support a Biologics License Application submission to the FDA in the first half of 2028.

Outlook

OPUS-1 moves VAX-31 from a promising mid-stage asset to a late-stage candidate with clean pivotal data in adults. Regulatory filing, manufacturing consistency and the infant program remain ahead, and the vaccine will not be available before the 2028 filing is reviewed. The competitive question for Pfizer and Merck is how quickly a 31-valent option could pressure their adult franchises once it reaches the market.