Pfizer Inc. PFE, -1.21% said Thursday a Phase 3 trial of older adults testing its bivalent RSV vaccine candidate achieved 85.7% efficacy in participants with more severe disease. RSV, or Respiratory Syncytial Virus, is a contagious virus that's defined by a group of respiratory symptoms that vary from mild to more severe. The virus affects the lungs and breathing passages of an infected individual and can be life-threatening to older and high-risk patients. About 336,000 older adults are hospitalized globally with the illness, said Pfizer, and there are currently no treatments or therapies. The late-stage trial involved about 37,000 patients aged 60 and older that were enrolled across the world. Enrollment up to about 40,000 participants is continuing in the Southern Hemisphere in order to get cases during their first season. Pfizer intends to use the data to submit a Biologics License Application (BLA) to the U.S. Food and Drug Administration. It will later prepare submissions to other regulators. Shares were slightly higher premarket, but are down 12% in the year to date, while the S&P 500 SPX, +0.29% has fallen 13%.