Vaxcyte has seen its stock jump after the biotech’s 31-valent pneumococcal vaccine candidate went head-to-head with Pfizer’s Prevnar 20 and Merck & Co.’s Capvaxive in a phase 3 contest.
The biotech evaluated its candidate, dubbed VAX-31, against those two approved vaccines in the late-stage Opus-1 study as a way to prevent invasive pneumococcal disease and pneumococcal pneumonia in adults.
VAX-31 showed non-inferiority on all 20 of the pneumococcal strains targeted by Prevnar 20 and 17 of the 19 serotypes targeted by Capvaxive, Vaxcyte explained in an Oct. 5 release. In this case, non-inferiority was defined as when the lower bound of the 95% confidence interval (LBCI) exceeded 0.667.
The serotypes where VAX-31 missed the non-inferiority criteria against Capvaxive were 3 and 12F, although Vaxcyte pointed out that even here, VAX-31 had still passed the lower, historical non-inferiority threshold of LBCI exceeding 0.5.
VAX-31 was well tolerated and demonstrated a safety profile similar to Pfizer’s and Merck’s approved vaccines across all ages studied, Vaxcyte noted.
Investors appeared buoyed by the news, sending the biotech’s stock up 57% in pre-market trading Monday to $88.50 from a Friday closing price of $56.48.
The vaccine’s ability to meet all the prespecified primary immunogenicity endpoints across all age groups will provide the “clinical cornerstone” for Vaxcyte’s approval application to the FDA, which is expected in the first half of 2028, CEO Grant Pickering said in the release.
“We believe VAX-31’s combination of broader coverage and robust immune responses, demonstrated in a trial inaugurating a more stringent noninferiority standard, sets a new benchmark for the class and gives us confidence in its potential for approval,” Pickering added.
The strains that are unique to Capvaxive account for a larger share of pneumococcal disease and pneumococcal pneumonia in U.S. adults, pointed out Vaxcyte’s Chief Scientific Officer and Chief Operating Officer James Wassil.
For this reason, the company expects the comparison between VAX-31 and Capvaxive to be a “particular focus” of the FDA’s approval decision.
“[Prevnar 20] remains an important immunogenicity comparator for VAX-31, including for serotypes 4 and 19F, which are not contained in [Capvaxive],” Wassil added.
Serotype 4 has been deemed important for health equity as it most often affects certain underrepresented populations.
“Today’s adult PCVs differ in the serotypes they cover, requiring tradeoffs between coverage of currently circulating disease-causing serotypes and preserving coverage of historically important serotypes,” Vaxcyte’s Chief Medical Officer Luis Jodar, Ph.D., said in the same release.
“VAX-31 is designed to bring both into a single 31-valent vaccine, with the potential to provide incremental coverage of 13-36% of invasive pneumococcal disease and 19-31% of pneumococcal pneumonia compared with currently available adult PCVs,” Jodar added.
Back in 2024, earlier-stage data suggesting VAX-31 was non-inferior to the 20 serotypes targeted by Prevnar 20 came as a surprise to some analysts because the additional carrier proteins required to handle the vaccine’s extra immunogen had been expected to reduce antibody responses for some serotypes. That’s typically seen as the trade-off to achieve wider serotype coverage.
Vaxcyte’s ability to include 31 serotypes is down to the biotech’s proprietary carrier-sparing technology. The platform allows for more precise conjugation of polysaccharides to the carrier protein in a way that preserves exposure of essential T-cell epitopes.
The company is also running two further phase 3 trials of VAX-31 in adults, called Opus-2 and Opus-3, with readouts penciled in for the first half of next year. Around that time, the biotech will also unveil data from a phase 2 study of the vaccine in infants.
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