Vaxcyte shares surge after positive Phase 3 vaccine results

On October 5, 2026, Vaxcyte said its experimental 31-valent pneumococcal vaccine, VAX-31, met the main immune-response goals in the pivotal adult Phase 3 OPUS-1 trial.

The 4,047-person trial found VAX-31’s immune responses were non-inferior to comparator vaccines for the serotypes assessed against Pfizer’s Prevnar 20 and Merck’s Capvaxive. The company also reported stronger responses for several additional serotypes. Safety and tolerability were described as comparable to the licensed vaccines.

Vaxcyte shares jumped roughly 50–57% in early trading following the announcement, according to reports.

The result is an important step, not an approval:
VAX-31 remains investigational. Vaxcyte expects results from two other adult Phase 3 trials, OPUS-2 and OPUS-3, in the first half of 2027, and has said it plans to seek FDA approval through a Biologics License Application.