Vaxcyte's 31-strain pneumococcal vaccine matches Pfizer and Merck shots in Phase 3

Vaxcyte reported on 5 October 2026 that VAX-31, its 31-valent pneumococcal conjugate vaccine, met all of its primary objectives in OPUS-1, the first of three Phase 3 studies in adults, in a head-to-head comparison with Pfizer's Prevnar 20 and Merck & Co.'s Capvaxive ¹². The randomised study enrolled just over 3,500 adults aged 50 and older, who received one of the three vaccines before investigators measured antibody responses strain by strain ³.

What the trial found

VAX-31 was non-inferior on all 20 serotypes in Prevnar 20 and on 17 of the 19 serotypes in Capvaxive ². The trial set non-inferiority as a lower bound of the 95% confidence interval above 0.667 ². The two misses against Capvaxive were serotypes 3 and 12F, and Vaxcyte said both still cleared the older threshold of 0.5 ². BioPharma Dive reported that the shot also proved superior on three strains that only it covers ¹.

The company said the vaccine was “well tolerated”, with a safety profile similar to both approved comparators at every age studied ¹². Most adverse events were “generally mild-to-moderate” and most resolved within two days ¹.

Chief executive Grant Pickering said meeting every prespecified primary immunogenicity endpoint across all age groups would form the “clinical cornerstone” of the company's filing with the FDA, which Vaxcyte expects in the first half of 2028 ². Chief medical officer Luis Jodar said VAX-31 could add coverage of 13-36% of invasive pneumococcal disease and 19-31% of pneumococcal pneumonia over the adult vaccines now available ². Fierce Biotech attributes the breadth to Vaxcyte's carrier-sparing conjugation platform, which was expected to cost antibody response at some serotypes but so far has not ².

What it means for the market

The result puts the most advanced challenger in front of a franchise Pfizer has long dominated. Pfizer's pneumococcal vaccines earned more than $6 billion last year, and Mizuho analyst Salim Syed values the market at $8 billion a year and rising ¹. Merck and GSK have both spent heavily on rival shots without loosening that hold ¹.

Investors read the data as better than feared. Executives had hinted in May that VAX-31 might fall short on some Capvaxive strains ¹. Vaxcyte shares rose 57% before the market opened, to $88.50 from a Friday close of $56.48, and BioPharma Dive put the company's value above $12 billion in early trading ¹². Syed called the readout a “near best-case scenario” ¹. Leerink Partners analyst David Risinger called missing on two strains only under a stricter framework “highly impressive” and argued they should not hurt approval odds, since VAX-31 only had to match one comparator on each shared strain ¹.

For Pfizer and Merck the question is now how the FDA weighs the Capvaxive comparison. Vaxcyte itself expects that comparison to be a “particular focus” of the review, because the strains unique to Capvaxive account for a larger share of US adult disease ². Prevnar 20 stays relevant as a comparator for serotypes 4 and 19F, which Capvaxive lacks; serotype 4 matters for health equity as it falls most often on some under-represented groups ².

Caveats

OPUS-1 compared antibody responses rather than counting cases of disease prevented, and it enrolled only adults aged 50 and older ¹³. The results are topline figures released by the company ². The extra coverage estimates are Vaxcyte's own and are framed against disease in US adults ².

Vaxcyte will seek approval only if two further Phase 3 trials are also positive ¹. Those studies, OPUS-2 and OPUS-3, are due to read out in the first half of next year, alongside Phase 2 data in infants ².