Merck’s Enflonsia (clesrovimab) has received FDA approval for the prevention of respiratory syncytial virus (RSV) lower respiratory tract disease (LRTD) in newborns and infants born during or entering their first RSV season. Enflonsia, is a long-acting monoclonal antibody (mAb) that can provide protection through a typical 5-month RSV season with a 105mg dose, regardless of weight. This diversifies the prophylactic options available to protect young children from RSV, with Enflonsia expected to become a key player in the US market, says GlobalData.
Anaelle Tannen, Infectious Disease Analyst at GlobalData, comments, “Enflonsia will now compete with Sanofi and AstraZeneca’s blockbuster drug Beyfortus (nirsevimab), for patient shares in the US*. The benefit of Enflonsia is that it is the first and only RSV preventative option for the paediatric market that does not require weight based-dosing, which makes administration easier and more convenient.”
The recent approval of Enflonsia was based on clinical trial results from the Phase IIb/III CLEVER trial evaluating a single dose of Enflonsia administered to preterm and full-term infants. Treatment with clesrovimab reduced medically attended RSV lower respiratory infections by 60.4 per cent and RSV-related hospitalisations by 84.2 per cent compared to placebo.
Tannen adds, “Both Beyfortus and Enflonsia have strong efficacy and safety profiles. Both are expected to completely replace the use of Sobi’s Synagis (palivizumab), an older mAb which requires monthly dosing throughout the RSV season and is associated with more toxicities, with side effects including fevers and rashes, among others.”
Merck plans to make Enflonsia available for the 2025-26 RSV season. Enflonsia is expected to become a successful drug in the pediatric market, reaching sales of $488 million in the US, and $892 million globally by 2031, according to GlobalData’s analyst consensus forecast. Nonetheless, GlobalData still expects Beyfortus to perform better commercially than Enflonsia over this time period since it is an earlier-market entrant with a similar safety and efficacy profile. Furthermore, unlike Enflonsia, Beyfortus is also approved for use in children up to 24 months who remain vulnerable to RSV through their second RSV season.
The CDC’s Advisory Committee on Immunisation Practices (ACIP) meeting is due to be held on 25-27th June when recommendations for RSV immunisations will be made. These recommendations are likely to heavily influence Enflonsia’s ability to capture market share from Beyfortus.
Tannen concludes, “With RSV being the leading cause of infant hospitalisation in the US, Enflonsia provides an alternative, convenient and efficacious option to prevent RSV LRTD in neonates and infants.”
*Beyfortus received FDA approval for the prevention of RSV LRTD in young children in July 2023.