Enflonsia (clesrovimab-cfor) / Merck (MSD) - LARVOL DELTA

Optimization of clesrovimab cell-based assay with improved precision and throughput. (PubMed, Biologicals) - "A comprehensive robustness study of the optimized clesrovimab cell-based assay has demonstrated fit-for-use assay performance by introducing small but deliberate variations of the selected assay parameters and reagents. The method was successfully validated and implemented for commercial release and stability testing of clesrovimab, and ultimately has been accepted by numerous global health authorities."

Journal • Infectious Disease • Respiratory Diseases • Respiratory Syncytial Virus Infections

The EMBRACE Study: Enflonsia Monoclonal in Babies - RSV Antibody Concentration Evaluation (clinicaltrials.gov) - P4 | N=24 | Not yet recruiting | Sponsor: Emory University

New P4 trial • Infectious Disease • Respiratory Diseases • Respiratory Syncytial Virus Infections

Mutational constraints on RSV F and its neutralization by antibodies. (PubMed, Nature) - "We then perform pseudovirus deep mutational scanning to safely measure how nearly all mutations to F affect its cell entry function and neutralization by IgG and Fab forms of nirsevimab, clesrovimab and several other key antibodies. We use these measurements to enable real-time surveillance of RSV sequences for antibody resistance, and show that resistant strains have arisen sporadically but are at present rare. Overall, our work shows how Fab potency and epitope specificity combine to determine how viral mutations affect antibody neutralization, enables monitoring for natural RSV strains resistant to antibodies of public-health importance, and can help guide development of future antibodies with resilience to viral escape."

Journal • Respiratory Diseases • Respiratory Syncytial Virus Infections

Impact of Clesrovimab on Commercially Available RSV Rapid Antigen Based Diagnostic Assays (IDWeek 2026) - No abstract available

Diagnostic assay • Infectious Disease

Anti Drug Antibody Responses to Clesrovimab Are Driven by Natural RSV Exposure Following Declining Protective Antibody Levels and Are Mitigated by Second-Season Dosing (IDWeek 2026) - No abstract available

Infectious Disease

Impact of Antidrug Antibodies on the Pharmacokinetics, RSV Serum-Neutralizing Activity, and Safety of Clesrovimab in a Phase 3 Trial (SMART) (IDWeek 2026) - No abstract available

Clinical • P3 data • PK/PD data • Infectious Disease

RSV Coinfection With Community Respiratory Pathogens Following Administration of Clesrovimab in the Phase 3 SMART Trial (IDWeek 2026) - No abstract available

P3 data • Infectious Disease

RSV Incidence Rates in RSV Season 2 of the Phase 3 SMART Trial of Clesrovimab: Impacts of Participant Population and RSV Circulation (IDWeek 2026) - No abstract available

Clinical • P3 data • Infectious Disease

Clesrovimab safety and exposure levels in infants under 2 kilograms: A subgroup analysis of the phase 3 SMART study (IDWeek 2026) - No abstract available

Clinical • P3 data • Infectious Disease

RSV Incidence Rates in RSV Season 2 of the Phase 3 SMART Trial of Clesrovimab: Impacts of Participant Population and RSV Circulation (IDWeek 2026) - No abstract available

Clinical • P3 data • Infectious Disease

Clesrovimab, a monoclonal antibody for the prevention of respiratory syncytial virus disease in infants: a drug profile. (PubMed, Expert Rev Respir Med) - "Respiratory syncytial virus (RSV) is a leading cause of acute lower respiratory tract infection (LRTI) in young children. Its epitope target is distinct from that of nirsevimab (site Ø) and no cross resistance between the two antibodies has been observed in vitro. Equitable global access to monoclonal antibodies, particularly for low- and middle-income countries, remains critical to reduce the global RSV burden."

Journal • Review • Infectious Disease • Pediatrics • Respiratory Diseases • Respiratory Syncytial Virus Infections

Respiratory Syncytial Virus Prophylaxis: Maternal Vaccination or Long-Acting Monoclonal Antibodies? A Brief Narrative Review of Current Status. (PubMed, Vaccines (Basel)) - "Long-acting monoclonal antibodies, including nirsevimab and clesrovimab, bypass maternal immune variability and provide standardized, season-long protection across gestational ages, including preterm infants. Global equity considerations remain critical: disparities in antenatal care access, supply chain fragility, and pricing differentials may widen gaps between high- and low-income countries. Remaining evidence gaps-including long-term safety monitoring, durability of protection, viral evolution, and implementation challenges-underscore the need for continued research and careful integration of these tools into national immunization programs."

Journal • Review • Infectious Disease • Respiratory Diseases • Respiratory Syncytial Virus Infections

A comprehensive look at Respiratory Syncytial Virus (RSV): from pathogenesis to prevention. (PubMed, Trop Dis Travel Med Vaccines) - "Until now, three RSV vaccines, Arexvy, Abrysvo, and mRESVIA, have received approval from the FDA. In addition, monoclonal antibodies such as Nirsevimab and Clesrovimab prevent severe RSV disease and are recommended for infants. Given the significant global impact of RSV, this narrative review addresses its multifaceted aspects, including epidemiology and global impact, clinical manifestations, therapeutic strategies, vaccine development, and its emerging potential as an oncolytic agent."

Journal • Review • Infectious Disease • Respiratory Diseases • Respiratory Syncytial Virus Infections

Prevalence and genetic diversity of respiratory syncytial viruses circulating in Bulgaria, 2023-2025. (PubMed, Front Cell Infect Microbiol) - "No substitutions were detected in the F protein antigenic sites of RSV-A (Ø, I-V), including the binding sites for nirsevimab (site Ø), palivizumab (site II), and clesrovimab (site IV). RSV is a leading cause of severe respiratory disease in early childhood and demonstrates substantial genetic diversity among circulating strains. The absence of resistance-associated substitutions in the F protein indicates that currently circulating RSV strains remain susceptible to approved mAbs."

Journal • Infectious Disease • Pneumonia • Pulmonary Disease • Respiratory Diseases • Respiratory Syncytial Virus Infections

The New Era of Respiratory Syncytial Virus Protection for Infants: A Mini Review of Current Tools for Immunoprophylaxis. (PubMed, Acta Paediatr) - "The newly introduced long-acting monoclonal antibodies and the maternal RSV vaccine have proved highly effective and have demonstrated reassuring safety. They have already been implemented in a number of countries and have substantially reduced the RSV burden in infants."

Journal • Review • Infectious Disease • Respiratory Diseases • Respiratory Syncytial Virus Infections

Summary of the National Advisory Committee on Immunization (NACI) Statement: Updated guidance to protect infants and children from respiratory syncytial virus disease. (PubMed, Can Commun Dis Rep) - "In March 2026, the National Advisory Committee on Immunization (NACI) released updated guidance reflecting new evidence on the monoclonal antibodies (mAbs) nirsevimab (Beyfortus®) and clesrovimab (Enflosia) and the RSVpreF pregnancy vaccine (Abrysvo)...At current product list prices, the combined pregnancy-infant program offers better value than a universal mAb program. Jurisdictions should consider local epidemiology, feasibility, cost-effectiveness considerations and equity when selecting a program model."

Journal • Critical care • Infectious Disease • Respiratory Diseases • Respiratory Syncytial Virus Infections

Merck…that the U.S. Food and Drug Administration (FDA) has accepted a supplemental Biologics License Application (sBLA) for ENFLONSIA (clesrovimab-cfor) to expand its indication to include prevention of respiratory syncytial virus (RSV) lower respiratory tract disease (LRTD) in children under two years of age at increased risk for severe RSV disease through their second RSV season. (Merck (MSD) Press Release) - "The FDA has set a Prescription Drug User Fee Act (PDUFA), or target action, date of March 22, 2027...In July 2026, the European Medicines Agency (EMA) accepted the application to expand marketing authorization for ENFLONSIA in the European Union (EU) for the same population...Both the U.S. and EU applications are supported by data from the Phase 3 SMART trial (MK-1654-007)..."

EMA filing • FDA filing • PDUFA • Immunology • Infectious Disease • Respiratory Syncytial Virus Infections

RSV Immunoprophylaxis in Infants and Children: Old Standards, New Agents and the Complexities Therein. (PubMed, Vaccines (Basel)) - "The recent approval of two second-generation long-acting mAbs, nirsevimab and clesrovimab, and maternal preF vaccine has fundamentally changed the RSV prevention landscape. Clesrovimab, as the newest agent, currently lacks real-world effectiveness, and both long-acting monoclonals require further confirmatory evidence in high-risk groups. Overall, existing data support that both monoclonals have equivalent efficacy and safety profiles as palivizumab, and choice should be based on cost-effectiveness and local availability, with consideration given to optimal integration of infant immunoprophylaxis alongside maternal RSV vaccination programmes."

Journal • Review • Infectious Disease • Respiratory Diseases • Respiratory Syncytial Virus Infections

Clesrovimab in Infants at Increased Risk For Severe Disease During 2 RSV Seasons: A Randomized Clinical Trial. (PubMed, JAMA Pediatr) - P3 | "To evaluate the safety and tolerability of clesrovimab (105 mg) vs palivizumab in RSV season 1 in infants at increased risk for severe RSV disease. These findings support the use of clesrovimab in children who remain at risk for severe RSV disease in their second RSV season. ClinicalTrials.gov Identifier: NCT04938830."

Clinical • Journal • Bronchopulmonary Dysplasia • Cardiovascular • Heart Failure • Infectious Disease • Pulmonary Disease • Respiratory Diseases • Respiratory Syncytial Virus Infections

RSV prophylactics for pediatric populations: A product review and meta-analysis of real-world effectiveness. (PubMed, Hum Vaccin Immunother) - "For decades, prophylaxis was limited to monthly palivizumab for selected high-risk infants...Across 43 observational studies, pooled effectiveness against RSV-associated hospitalization was 80.9% for nirsevimab and 79.1% for maternal RSVpreF vaccination, demonstrating substantial real-world protection during early infancy. Success now depends on optimizing implementation and achieving equitable access."

Clinical • Journal • Real-world evidence • Retrospective data • Review • Infectious Disease • Pediatrics • Respiratory Diseases • Respiratory Syncytial Virus Infections

Evaluating respiratory syncytial virus immunization strategies for infants in Canada: A cost-utility analysis. (PubMed, PLoS One) - "A seasonal combination program with RSVpreF for in-season deliveries and mAb for infants at high risk of RSV offers the best value for money for protecting Canadian infants from RSV disease. Broader infant immunization programs may be cost-effective with substantial price reductions or in regions with higher disease burden and healthcare costs."

HEOR • Journal • Infectious Disease • Respiratory Diseases • Respiratory Syncytial Virus Infections

MODELING THE CLINICAL IMPACT OF CLESROVIMAB FOR RESPIRATORY SYNCYTIAL VIRUS PREVENTION IN INFANTS IN CHINA (ESPID 2026) - "Compared with nirsevimab, clesrovimab was projected to prevent an additional 367 (11.4%) hospitalizations, 149 (11.4%) ICU admissions, 9,208 (11.4%) outpatient visits, and 3 (11.1%) in- hospital deaths among infants. Conclusions/Learning Points Both nirsevimab and clesrovimab were estimated to significantly reduce RSV-related clinical burden among infants in China, with clesrovimab resulting in a greater health impact than nirsevimab."

Clinical • Infectious Disease • Respiratory Syncytial Virus Infections

Late-Breaking Abstract: MODELING THE CLINICAL AND ECONOMIC IMPACT OF CLESROVIMAB FOR RESPIRATORY SYNCYTIAL VIRUS PREVENTION IN INFANTS IN SPAIN (ESPID 2026) - "Country-specific data were used to evaluate clesrovimab versus nirsevimab assuming 90% coverage for both on 317,845 infants. Analogous trend of results was observed for other scenarios. Conclusions/Learning Points Clesrovimab resulted in lower clinical and economic burden of RSV among infants in Spain, supporting its potential value as a preventive strategy across infant subgroups."

Clinical • HEOR • Late-breaking abstract • Infectious Disease • Respiratory Syncytial Virus Infections

Enflonsia (clesrovimab) and the future of RSV lower respiratory tract disease prevention in neonates. (PubMed, Ann Med Surg (Lond)) - "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. 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."

Journal • Immunology • Respiratory Diseases • Respiratory Syncytial Virus Infections

Advancements in Respiratory Syncytial Virus (RSV) Prevention and Treatment in Pediatrics. (PubMed, J Pediatr Pharmacol Ther) - "This review aimed to synthesize and evaluate existing data on the approved RSV preventative therapies nirsevimab, RSVpreF, clesrovimab, and palivizumab. RSV disease, including its spread, virology, diagnosis, clinical presentation, and treatment, is also discussed."

Journal • Infectious Disease • Pediatrics • Respiratory Diseases • Respiratory Syncytial Virus Infections