Anushua Sinha, MD, MPH, highlights antibody for sustained RSV risk protection in infants

In a recent interview for Contemporary Pediatrics, Anushua Sinha, MD, MPH, Lead Clinical Director for the ENFLONSIA program at Merck, discussed the significance of the SMART trial results regarding respiratory syncytial virus (RSV) protection.

RSV remains a leading cause of infant hospitalization globally and the leading cause in the United States. ENFLONSIA (clesrovimab; Merck), a long-acting monoclonal antibody developed by Merck, received FDA approval in June 2025 to prevent RSV in infants entering their first season. Sinha emphasized that while all infants are at risk, the SMART trial specifically addressed those at increased risk for severe disease, including those born preterm or with underlying conditions such as chronic lung disease and congenital heart disease.

The SMART trial serves as a pivotal study to bridge efficacy data from healthy infants, established in the CLEVER trial, to those with complex medical needs. Because ENFLONSIA is designed to target the viral F protein without interacting with the host, clinical protection is dependent on achieving specific serum concentrations.

Sinha explainedt hat if the same concentration is achieved in high-risk infants as in healthy ones, the efficacy can be successfully "bridged." Data from the SMART trial's second season confirmed that these efficacious concentrations were met in children aged less 2 years with chronic lung or congenital heart disease.

The discussion also addressed the durability of protection for older children with greater body mass entering their second RSV season. In the first season of the SMART study, infants were randomized to receive 105 mg of ENFLONSIA or monthly palivizumab. For the second season, eligible participants—including those with chronic lung disease or congenital heart disease—received an open-label 210 mg dose.

This higher dose was designed to account for increased body mass while maintaining the necessary area under the curve (AUC) from day 1 to day 150. Sinha noted that the AUC is the critical metric for measuring exposure over time throughout a typical 5-month RSV season.

By achieving a comparable AUC with the 210 mg dose, the data suggests that these vulnerable children maintain the necessary protective levels of the antibody. Ultimately, the SMART trial provides pediatricians with the evidence needed to confidently recommend ENFLONSIA for high-risk children entering their second season, ensuring they receive the same level of protection seen in healthy infants during their initial exposure.

Disclosure: Merck.

This video is part 1 of a 2-part series. Click here for part 2.

Reference

Merck announces positive new data for Enflonsia (clesrovimab) for infants and children under 2 years of age at increased risk for severe respiratory syncytial virus (RSV) disease over two RSV seasons. News release. Merck. February 19, 2026. March 5, 2026. https://www.businesswire.com/news/home/20260219213035/en/Merck-Announces-Positive-New-Data-for-ENFLONSIA-clesrovimab-for-Infants-and-Children-Under-2-Years-of-Age-at-Increased-Risk-for-Severe-Respiratory-Syncytial-Virus-RSV-Disease-Over-Two-RSV-Seasons