Wall Street promptly began trying to weigh the compound’s marketplace odds after Merck & Co. Inc. detailed positive data from the phase IIb/III trial known as MK-1654-004 with clesrovimab, an investigational prophylactic monoclonal antibody designed to protect infants from respiratory syncytial virus (RSV) disease during their first RSV season. The results, plus interim findings from the ongoing phase III experiment dubbed MK-1654-007 were offered during IDWeek 2024 in Los Angeles.

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.