Many respiratory syncytial virus (RSV) disease vaccines are for older adults but Merck & Co. Inc.’s monoclonal antibody, MK-1654 (clesrovimab), which just produced positive top-line phase IIb/III data, aims at a far smaller and younger market. Data for protecting healthy preterm and full-term infants from RSV disease show the double-blind, randomized, placebo-controlled clinical trial hit all its primary efficacy and safety endpoints, including the incidence of RSV-associated medically attended lower respiratory infection for 150 days compared to placebo.