Merck’s clesrovimab lowered the risk of medically attended lower respiratory infections associated with RSV infection when used in infants, according to topline results announced Tuesday.
Merck on Tuesday announced topline Phase IIb/III results for its investigational respiratory syncytial virus prophylactic antibody clesrovimab, touting a strong protective effect against the virus in infants.
The pharma did not provide specific data in its announcement, only revealing that clesrovimab reduced the incidence of medically attended lower respiratory infections (MALRI), as caused by the respiratory syncytial virus (RSV), through 150 days. Merck will present detailed findings and analyses from the study at an upcoming medical congress.
Paula Annunziato, Merck’s senior vice president of infectious diseases and vaccines clinical research, in a statement said that the pharma is “encouraged” by these results. The company plans to file these data with global regulatory authorities “to provide a new option to help address the impact of RSV on infants and their families,” Annunziato said.
Clesrovimab is a fully human, extended half-life monoclonal antibody that induces passive immunity against RSV by binding to the fusion glycoprotein of the virus, preventing it from infiltrating host cells. Merck is trialing clesrovimab in infants to assess whether a single dose can safely and rapidly provide durable protection against infection.
Tuesday’s readout comes from the MK-1654-004 Phase IIb/III trial, a randomized, double-blinded and placebo-controlled study that enrolled more than 3,600 healthy preterm or full-term infants—those who were delivered with at least 29 weeks of gestation. The trial’s primary endpoint is MALRI, measured 150 days after the clesrovimab dose. MK-1654-004 was also designed to evaluate the antibody’s safety, though Merck has yet to provide these findings.
With these latest results for clesrovimab, Merck is gearing up to challenge AstraZeneca and Sanofi’s Beyfortus (nirsevimab), which is also a prophylactic antibody designed to prevent RSV infection in infants and toddlers. The FDA approved Beyfortus in July 2023 allowing its use in newborns entering their first RSV season, or those up to 24 months old and who are at severe risk of infection entering their second RSV season.
Like clesrovimab, Beyfortus works by binding to a specific part of the virus and preventing it from entering host cells. Its approval was supported in part by data from the MELODY and MEDLEY studies, which together showed that Beyfortus was safe to use in infants and could reduce RSV-associated respiratory tract infections requiring medical attendance by almost 75%. The antibody also cut hospitalizations by around 60%.
In March 2024, the Centers for Disease Control and Prevention released an analysis of Beyfortus’ real-world usage, showing that the antibody could reduce RSV-associated hospitalizations by 90%.
