Nirsevimab-alip (Beyfortus) has been approved by the Food and Drug Administration to prevent respiratory syncytial virus (RSV) in neonates and infants born during or right before their first RSV season (fall through winter) and in children up to 24 months of age who continue to be vulnerable to severe RSV disease in their second RSV season. Monoclonal antibodies are not vaccines. They are laboratory-made proteins that help boost the body's immune response and decrease the risk of serious symptoms requiring hospitalization. Nirsevimab-alip, given once via injection at the start of RSV season, is the second monoclonal antibody approved to prevent RSV. The first, palivizumab (Synagis), must be given monthly during the RSV season.
RSV is a common respiratory virus that affects all age groups. Almost all children will have had an RSV infection by the time they are two years old. While the virus often presents with mild, cold-like symptoms, severe illnesses such as bronchiolitis and pneumonia are possible. According to the American Academy of Pediatrics, approximately 1% to 3% of U.S. children under 12 months of age are hospitalized each year because of RSV. Children at greatest risk for severe illness, according to the Centers for Disease Control and Prevention, are premature infants; infants ages 12 months and younger, especially those six months and younger; children younger than two years with chronic lung disease or congenital heart disease; children with weakened immune systems; and children who have neuromuscular disorders, including those who have difficulty swallowing or clearing mucus secretions.
Early symptoms of RSV include runny nose, eating or drinking less, and a cough that can progress to wheezing or difficulty breathing. More serious symptoms in the very young include irritability, decreased activity, eating or drinking less, and apnea (lasting more than 10 seconds). Fever may not always occur with RSV infections.
The safety and effectiveness of nirsevimab-alip was supported in three clinical trials. The product's effectiveness was determined by the incidence of medically attended RSV lower respiratory tract infections in the 150 days after the drug was given. Two of the trials were randomized, double-blind, placebo-controlled, multicenter clinical trials, both of which showed that nirsevibab-alip reduced the risk of RSV requiring medical attention compared with placebo. A third trial was an active-controlled trial where nirsevimab-alip or palivizumab was given to children up to 24 months of age who were premature or who had been born with chronic lung or heart disease. In this trial, a similar safety profile was demonstrated whether nirsevimab-alip was given for two RSV seasons or for only one season. Data comparing the effectiveness of the two drugs were not provided.
Similar to that of other human immunoglobulin G1 monoclonal antibodies, nirsevimab-alip's labeling carries a warning of serious hypersensitivity reactions. The most common adverse effects are rash and injection site reactions.
For complete prescribing information for nirsevimab-alip, see http://www.accessdata.fda.gov/drugsatfda_docs/label/2023/761328s000lbl.pdf.