The Food and Drug Administration (FDA) has approved Beyfortus (nirsevimab-alip) for the prevention of respiratory syncytial virus (RSV) lower respiratory tract disease in neonates and infants born during or entering their first RSV season, and in children up to 24 months of age who remain vulnerable to severe RSV disease through their second RSV season.

Nirsevimab is a long-acting anti-RSV monoclonal antibody that is administered as a single dose timed to the RSV season. The approval was based on data from the nirsevimab clinical development program, which included a phase 2b trial ( Identifier: NCT02878330), the phase 3 MELODY trial ( Identifier: NCT03979313), and the phase 2/3 MEDLEY trial ( Identifier: NCT03959488).

In the phase 2b trial, infants who were born during or entering their first RSV season were randomly assigned to receive a single dose of Beyfortus (n=969) or placebo (n=484). Findings showed that treatment with Beyfortus significantly reduced the incidence of medically-attended lower respiratory tract disease caused by RSV by 70.1% (95% CI, 52.3-81.2; P <.001) compared with placebo. There were 25 cases reported in the Beyfortus group and 46 cases reported in the placebo group.

Continue Reading

The MELODY trial compared a single intramuscular (IM) injection of nirsevimab to placebo in 1490 healthy infants who were born at a gestational age of at least 35 weeks. Findings showed that treatment with nirsevimab was associated with a statistically significant reduction in the incidence of medically-attended RSV-associated lower respiratory tract infection (LRTI) and a lower incidence of hospitalization for RSV-associated LRTI compared with placebo. 

In the randomized, double-blind MEDLEY trial, the safety and tolerability of nirsevimab were compared with palivizumab in approximately 925 infants with congenital heart disease, chronic lung disease, and/or prematurity before entering their first RSV season. Findings showed that nirsevimab demonstrated a similar safety and tolerability profile compared with palivizumab. 

“Today’s approval marks an unprecedented moment for protecting infant health in the US, following an RSV season that took a record toll on infants, their families, and the US healthcare system,” said Thomas Triomphe, executive vice president, Vaccines, Sanofi. “Beyfortus is the only monoclonal antibody approved for passive immunization to provide safe and effective protection for all infants during their first RSV season.” 

The most common adverse reactions reported with Beyfortus were rash and injection site reactions. Beyfortus carries a risk for serious hypersensitivity reactions, including anaphylaxis. Health care providers should exercise caution when administering to infants and children with clinically significant bleeding disorders.

Beyfortus is supplied as a 50 mg/0.5 mL and 100 mg/ mL prefilled syringe. The product is expected to be available for the upcoming 2023-2024 RSV season.


  1. US Food and Drug Administration. FDA approves new drug to prevent RSV in babies and toddlers. News release. July 17, 2023.
  2. Press Release: FDA approves Beyfortus (nirsevimab-alip) to protect infants against RSV disease. News release. Sanofi-Aventis Groupe. July 17, 2023.

This article originally appeared on MPR