The U.S. Food and Drug Administration on Thursday expanded the use of Moderna's respiratory syncytial virus vaccine to a lower group of adults aged 18 to 59 years at increased risk for disease. Moderna's RSV shot,

The FDA's approval was based on a study of 11,400 people age 12 and older that compared the new low-dose vaccine with Moderna's existing vaccine. It found the new vaccine was safe and was at least as effective - and more by some measures - than the original shot, the company said.