Vaxcyte unveiled what analysts called “stunning” phase 1/2 data for its 31-valent pneumococcal vaccine candidate that, if replicated in a large pivotal study, could pose a serious threat to Pfizer’s stalwart Prevnar 20.
The phase 1/2 Prevnar 20 head-to-head data that Vaxcyte revealed for its VAX-31 in adults ages 50 and older are “exceptional” and suggest “a pneumococcal conjugate vaccine category killer profile,” Leerink Partners analysts said in a Tuesday note.
“We believe the data support strong likelihood that VAX-31 could achieve majority market share in what we expect to be a >$10B pneumococcal conjugate vaccine market in 2030+,” Leerink analysts said.
Thanks to the positive readout, which Mizuho analysts called a “best-case scenario,” Vaxcyte’s stock price jumped about 44% by publication time Tuesday morning.
“Today, we are entering a new chapter for Vaxcyte as we transition from upstart to potential powerhouse,” the company’s co-founder and CEO, Grant Pickering, said during an investor call Tuesday.
One key point from the readout that excited analysts is the fact that VAX-31, at both the middle and high doses, showed antibody immune responses—as measured by opsonophagocytic activity assay—that either matched or exceeded those of Prevnar 20 for the 20 serotypes shared between the two shots.
For the middle dose, VAX-31 had a geometric mean ratio (GMR) greater than 1 compared to Prevnar 20 in 13 of the 20 serotypes and achieved statistically higher immune responses in five stereotypes. For the high dose, 18 serotypes had a GMR higher than 1 and seven serotypes were deemed statistically higher than for Prevnar 20.
On average, immune responses for the shared serotypes were 25% higher for the high dose and 10% higher for the middle dose with VAX-31, Leerink analysts summarized.
VAX-31 meeting noninferiority on all 20 serotypes was a surprise to analysts because the additional carrier proteins required to handle the vaccine’s extra immunogen are expected to reduce antibody responses for some serotypes. That’s the trade-off to achieve wider stereotype coverage. As Leerink analysts pointed out, many analysts previously figured that VAX-31’s high dose would miss noninferiority on about three of the 20 shared serotypes.
Vaxcyte’s ability to include 31 serotypes has the biotech’s proprietary carrier-sparing technology to thank. The platform allows for more precise conjugation of polysaccharides to the carrier protein in a way that preserves exposure of essential T-cell epitopes, according to the company.
Besides all serotypes covered by the Pfizer shot, VAX-31 contains 11 additional serotypes. For the serotypes that are unique to VAX-31, the Vaxcyte shot on all three doses tested was superior to the Pfizer option.
By covering 31 serotypes, VAX-31 was designed to prevent more than 95% of invasive pneumococcal disease circulating in adults 50 and older in the U.S. In contrast, Prevnar 20 could cover 52% of the disease burden in the age group, and Merck & Co.’s newly approved Capvaxive targets 84%.
Given the positive data, Mizuho analysts suggested that VAX-31 has the potential to displace Prevnar 20 and maybe even Capvaxive, although the team cautioned that authorities would likely leave some redundancy in the system by allowing for multiple players. VAX-31 also holds an advantage over Capvaxive because it includes serotype 4, which was of particular interest to the CDC’s Advisory Committee on Immunization Practices during the group’s June meeting, Leerink analysts pointed out in an earlier note.
The Merck shot doesn’t include serotype 4, which is deemed important for health equity as it most often affects certain underrepresented populations.
The overwhelmingly positive topline phase 1/2 data also created a happy problem for Vaxcyte—choosing the right phase 3 dose. As the biotech weighs its options, Vaxcyte is still parsing through additional data, including prespecified age cohort analyses, CEO Pickering said on Tuesday’s call.
“We’ll look at the totality of the data as we move toward a decision,” Pickering said. “Obviously using less material to drive the immune responses creates an efficiency. But creating higher immune response, as long as we didn’t see any safety delta, is also attractive.”
Following a meeting with the FDA, the company plans to start a pivotal phase 3 trial by mid-2025, with topline results expected in 2026.
Besides VAX-31, Vaxcyte is also developing VAX-24, a 24-valent candidate for which the company expects to report topline safety and immunogenicity data from a phase 2 infant study by the first quarter of 2025. A separate phase 2 trial in infants for VAX-31 is planned to start early next year.