Vaxcyte shares $PCVX jumped more than 35% 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.
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.
Vaxcyte plans to launch a Phase 3 non-inferiority study in mid-2025 with topline data expected in 2026. The company will select a dose sometime before then.