Enflonsia (clesrovimab) and the future of RSV lower respiratory tract disease prevention in neonates

Abstract

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract disease in infants, with the highest burden in those under 6 months of age. Global RSV epidemics occur seasonally and nearly all children are infected within the age of 2 years, resulting in significant hospitalizations, morbidity, and healthcare costs. Enflonsia™ (clesrovimab-cfor), recently approved by the U.S. Food and Drug Administration, is a long-acting recombinant monoclonal antibody targeting the prefusion F protein of RSV, preventing viral entry and replication. A single intramuscular dose provides protection across the RSV season, eliminating the need for monthly injections. Clinical trials indicate that clesrovimab reduces RSV-related hospitalizations by up to 76% and medically attended RSV disease by over 70%, with a safety profile comparable to existing antibodies like palivizumab and nirsevimab. Common adverse events include mild injection-site reactions and rare hypersensitivity. While its high cost and cold-chain requirements may limit accessibility in low- and middle-income countries, the single-dose, season-long protection offers logistical advantages and potential cost-effectiveness in high-burden settings. Enflonsia represents a significant advance in infant RSV prophylaxis, with implications for global health strategies, integration into immunization programs, and equitable access to reduce RSV morbidity worldwide.