Vaxcyte (NASDAQ:PCVX) shares added ~32% premarket Tuesday after announcing that its experimental pneumococcal conjugate vaccine (PCV) VAX-31 indicated a safety profile similar to Pfizer’s (NYSE:PFE) rival shot Prevnar 20 in a Phase 1/2 trial.

Based on topline data from the study, the company said VAX-31 at all doses was well tolerated over a six-month evaluation period, similar to Prevnar 20. The study enrolled more than 1,000 healthy adults aged 50 and older.

As for immunogenicity, the vaccine candidate indicated opsonophagocytic activity (OPA) immune responses against 31 serotypes of the bacteria. However, compared to PCV20, the average OPA immune responses were higher for 18 of 20 serotypes at the VAX-31 high dose.

Based on the results, Vaxcyte (PCVX) intends to advance VAX-31, the broadest-spectrum PCV candidate in the clinic, into an adult Phase 3 program.

A pivotal Phase 3 study is expected to start in mid-2025, with topline data planned for 2025. The company expects to begin the remaining Phase 3 trials in 2025 and 2026 to prepare a marketing application for the candidate.