Nirsevimab, sold under the brand name Beyfortus, is a human recombinant monoclonal antibody with activity against respiratory syncytial virus (RSV).
It is a respiratory syncytial virus (RSV) F protein‑directed fusion inhibitor.
It binds to the fusion protein on the surface of the RSV virus.
Nirsevimab binds to the prefusion conformation of the RSV fusion (F) protein, i.e. it binds to the site at which the virus would attach to a cell; effectively rendering it useless.
It has a modified Fc region, extending the half-life of the drug in order for it to last the whole RSV season.
Routes of administration Intramuscular
The most common side effects are rash, fever and injection site reactions (such as redness, swelling and pain where the injection is given).
It indicated for the prevention of respiratory syncytial virus RSV lower respiratory tract disease in neonates and infants during their first RSV season.
Indicated for the prevention of RSV lower respiratory tract disease in neonates and infants born during or entering their first RSV season and children up to 24 months of age who remain vulnerable to severe RSV disease through their second RSV season.
CDC recommended maternal RSVpreF vaccination during pregnancy, though both are not needed in most infants.
It has a modified Fc region, extending the half-life of the drug in order for it to last the whole RSV season.
Nirsevimab prevents lower respiratory tract infection caused by RSV requiring medical attention such as bronchiolitis and pneumonia, in term and preterm infants during their first RSV season.
In a phase II/III, randomized, double‑blind, multicenter trial in infants who were born five or more weeks prematurely (less than 35 weeks gestation) at higher risk for severe RSV disease and infants with chronic lung disease of prematurity (i.e. long-term respiratory problems faced by babies born prematurely) or congenital heart disease: results of this study showed that nirsevimab had a similar safety profile compared to palivizumab (Synagis).
The US Food and Drug Administration (FDA) evaluated the safety and efficacy of nirsevimab based on three trials, two of which were randomized, double-blind, placebo-controlled, multicenter clinical trials.
The key measure of efficacy was the incidence of medically attended RSV lower respiratory tract infection (MA RSV LRTI), evaluated during the 150 days after nirsevimab administration.
MA RSV LRTI included all health care provider visits (physician office, urgent care, emergency room visits and hospitalization) for lower respiratory tract disease with worsening clinical severity and a positive RSV test.
Trial 03 included 1,453 preterm infants (born at greater than or equal to 29 weeks of gestational age up to less than 35 weeks of gestation) who were born during or entering their first RSV season.
Of the 1,453 preterm infants in the trial, 969 received a single dose of nirsevimab and 484 received placebo.
Among infants who were treated with nirsevimab, 25 (2.6%) experienced MA RSV LRTI compared with 46 (9.5%) infants who received placebo.
Nirsevimab reduced the risk of MA RSV LRTI by approximately 70% relative to placebo.
For Trial 04, the primary analysis group within the trial included 1,490 term and late preterm infants (born at greater than or equal to 35 weeks in gestational age), 994 of whom received a single dose of nirsevimab and 496 of whom received placebo.
Among infants who were treated with nirsevimab, 12 (1.2%) experienced MA RSV LRTI compared with 25 (5.0%) infants who received placebo.
Nirsevimab reduced the risk of MA RSV LRTI by approximately 75% relative to placebo.
Trial 05, a randomized, double-blind, active (palivizumab)-controlled, multicenter trial, supported the use of nirsevimab in children up to 24 months of age who remain vulnerable to severe RSV disease through their second RSV season.
The trial enrolled 925 preterm infants and infants with chronic lung disease of prematurity or congenital heart disease.
The safety and pharmacokinetic data from Trial 05 provided evidence for the use of nirsevimab to prevent MA RSV LRTI in this population.
Alternatively, the CDC recommended maternal RSVpreF vaccination during pregnancy, though both are not needed in most infants.
No major hypersensitivity reactions have been reported, and adverse events of grade 3 or higher were only reported in 8% (77 of 968) of participants in clinical trial.