MSD has received US Food and Drug Administration (FDA) approval for Enflonsia (clesrovimab-cfor) to prevent respiratory syncytial virus (RSV) lower respiratory tract disease in neonates and infants.
Enflonsia is a long-acting monoclonal antibody developed to offer speedy, direct and durable protection throughout a typical five-month RSV season with a consistent 105mg dose regardless of bodyweight.
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The approval is based on data from the pivotal Phase IIb/III CLEVER trial assessing a single dose of the antibody administered to both preterm and full-term infants up to one year old.
The study successfully met its primary and key secondary endpoints, demonstrating significant efficacy in reducing medically attended lower respiratory infections associated with RSV.
Enflonsia showed a 60.5% reduction in the incidence of these infections compared to placebo over five months.
Its key secondary endpoint demonstrated an 84.3% decrease in hospitalisations due to RSV-associated conditions over five months.
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By GlobalDataResults from the Phase III SMART trial, in which Enflonsia’s safety profile was assessed against palivizumab among infants at heightened risk for severe RSV illness, supported the approval.
MSD research laboratories president Dean Li stated: “Enflonsia provides an important new preventive option to help protect healthy and at-risk infants born during or entering their first RSV season with the same dose regardless of weight.
“We are committed to ensuring availability of Enflonsia in the US before the start of the upcoming RSV season to help reduce the significant burden of this widespread seasonal infection on families and health care systems.”
In May 2025, Daiichi Sankyo and MSD voluntarily withdrew the biologics licence application (BLA) in the US for their HER3-directed DXd antibody drug conjugate (ADC) patritumab deruxtecan, intended to treat non-small cell lung cancer.
