Vaxcyte said its experimental pneumococcal vaccine VAX-31 met key endpoints in a Phase 3 trial in adults age 50 and older, triggering a sharp stock move reported as a 35% gain. The company positioned VAX-31 as a 31-serotype vaccine aimed at competing with Pfizer’s Prevnar and Merck’s Capvaxive. In the trial, investigators randomized just over 3,500 adults to VAX-31, Prevnar, or Capvaxive and measured antibody responses across strains. A separate report framed the data as near best-case versus expectations across nearly all bacterial serotypes in the first of three Phase 3 studies. If regulatory outcomes follow, the readout could strengthen Vaxcyte’s ability to challenge incumbent pneumococcal franchises, where breadth of serotype coverage and immunogenicity breadth are key differentiators.