Federal health advisers are backing a first-of-its-kind RSV vaccine to protect newborns by immunizing their moms late in pregnancy. The virus fills hospitals with wheezing babies each winter. Pfizer's research shows a late-pregnancy shot is 82% effective at preventing severe RSV in the infants' first months of life. The Food and Drug Administration asked if there's a hint that the vaccine might affect premature birth but its advisers weren't convinced. The FDA recently approved a different RSV vaccine for older adults, the world's first made by rival GSK. FDA will consider Thursday's recommendation in deciding the fate of Pfizer's maternal vaccine.