Vaxcyte shares $PCVX jumped more than 40% Tuesday morning on the heels of Phase 1/2 data for its 31-valent pneumococcal conjugate vaccine, VAX-31, being tested in adults over 50.
The company tested three dose levels and measured them against Prevnar 20 in an observer-blind study. At both the middle and high doses, Vaxcyte said VAX-31 showed non-inferior immune responses for all 20 serotypes that are shared with Prevnar 20, as measured by opsonophagocytic activity (OPA) levels.
Additionally, at the high dose, the average OPA immune response was greater for 18 of the 20 common serotypes by a “geometric mean ratio,” or GMR, of at least 1.0. Seven of those serotype responses were higher by a statistically significant measure.
The middle dose saw 13 of the common 20 serotypes achieve a GMR of at least 1.0 and five were significantly higher. Across all three doses, VAX-31 met the trial’s superiority criteria for the 11 serotypes not shared with Prevnar 20.
Vaxcyte plans to launch a Phase 3 non-inferiority study in mid-2025 with topline data expected in 2026. The company chose to move VAX-31 into a pivotal trial in this indication over another internal program, VAX-24, on the strength of the data presented Tuesday, CEO Grant Pickering said on an investor call.
“Our VAX-24 adult data were stellar, but these VAX-31 results make it crystal clear it is the program to advance into the adult population,” Pickering said.
Vaxcyte has not yet selected which dose it will bring into Phase 3 studies. Execs also said they are planning to launch a Phase 2 study in infants in the first quarter of 2025.
Mizuho analyst Salim Syed said last month that, on an “individual serotype basis,” an OPA GMR of at least 0.6 would constitute a success for the trial — anything higher is likely predictive of a Phase 3 win. In the aggregate, a success would be defined by “six serotypes or less” failing to hit the 0.6 threshold, though Syed said there’s some wiggle room given the field’s nuances.
In another note to investors this morning, Syed said Tuesday’s results represent the “best-case scenario” for the trial. He also said this is the first time that Vaxcyte discussed a trial in infants for VAX-31, noting that adult data have historically been consistent with those in infants.
Editor’s note: This story has been updated with additional information following Vaxcyte’s Tuesday morning investor call.