Vaxcyte's pneumococcal jab exceeds expectations

Shares in Vaxcyte have rocketed on the revelation of phase 3 trial data for its pneumococcal vaccine (PCV) candidate VAX-31, which suggests it could be a threat to already-marketed shots from Pfizer and MSD.

Vaxcyte's stock was trading up nearly a third – driving its market cap towards $11 billion – as investors responded to the result of the first of three phase 3 trials of VAX-31, which is designed to protect against 31 serotypes of Streptococcus pneumoniae.

The vaccine met all of its main efficacy objectives in the 4,000-subject OPUS-1 study, including matching the efficacy of Pfizer's Prevnar 20 and Merck & Co.'s Capvaxive on the 20 and 21 pneumococcal strains, respectively, that they have in common.

All told, VAX-31 was at least as effective at all 28 serotypes covered by the two competing vaccines, while also protecting against three additional, unique strains, and was well-tolerated with a safety profile similar to Prevnar 20 and Capvaxive. The result suggests that the new vaccine could "deliver broader coverage while maintaining the magnitude of immune responses," said Vaxcyte.

The only issue in the results was a slightly lower protective efficacy against two strains covered by Capvaxive, using a more stringent statistical comparison, but that did not seem to dampen the enthusiasm of investors for the readout.

If VAX-31's promise is borne out in subsequent trial readouts, Vaxcyte could have a shot at taking on the established PCV incumbents, whose vaccines bring in billions of dollars in worldwide sales every year and could reach a value of $12 billion by 2030.

Pfizer's long-established Prevnar range made around $3 billion in the first six months of 2026, with Capvaxive an also-ran with a tally of $325 million in the same period – albeit with strong growth since its debut in the US in 2024.

Vaxcyte said the OPUS-1 data will be "the cornerstone" of a data package for filing of VAX-31 with the FDA. On an investor call, it said that the new shot offered an incremental 13% to 36% increase in coverage of strains involved in invasive pneumococcal disease (IPD) and 19% to 31% broader coverage of those that are linked to pneumococcal pneumonia – the two most serious complications of pneumococcal infections.

Vaxcyte's other two phase 3 studies are OPUS-2, looking at concomitant use of VAX-31 with the seasonal flu vaccine, and OPUS-3 involving adults previously vaccinated with other PCVs. Both follow-up studies have completed enrolment, with results due in the first half of next year.

"Today's adult PCVs differ in the serotypes they cover, requiring trade-offs between coverage of currently circulating disease-causing serotypes and preserving coverage of historically important serotypes," said Luis Jodar, Vaxcyte's recently appointed chief medical officer, who was formerly at Pfizer.

"VAX-31 is designed to bring both into a single 31-valent vaccine."