RSV Season is Here: Monoclonal Antibodies for Prophylaxis in Infants
Lilian White, MD
October 19, 2026
Respiratory syncytial virus (RSV) is the most common pathogen that causes lower respiratory tract infections in young children. RSV infects an estimated 90% of infants and children by age 2. RSV is the most common cause of hospitalization in infants in the United States with 58,000 to 80,000 hospitalizations and 100 to 300 deaths in children younger than 5. Children under the age of 2 (with the highest rate among those 0-2 months) and babies born prematurely are associated with an increased risk of hospitalization. In adults, RSV caused an estimated 466,000 hospitalizations in those older than 60 and 33,000 deaths in 2019.
Prevention of RSV in infants consists of promoting passive immunity through maternal immunization during pregnancy or monoclonal antibodies for infants. One-time immunization is recommended between 32-36 weeks’ gestation during RSV season (mid-September through January in most of the United States) and was reviewed in more detail in a previous AFP Community Blog post. Vaccination is not currently recommended for infants due to their inability to mount an adequate active immune response before peak risk of serious infection (0-2 months) and previous trials resulting in vaccine-enhanced respiratory disease; however, there are several trials underway to develop a vaccine for toddlers and older children.
Monoclonal antibodies for the prevention of RSV were approved by the US Food and Drug Administration with palivizumab (Synagis) in 1998, nirsevimab (Beyfortus) in 2023, and clesrovimab (Enflonsia) in 2025. Current indications for nirsevimab and clesrovimab include infants younger than 8 months who were born during or are entering their first RSV season whose mothers did not receive RSV vaccine during pregnancy. Nirsevimab is recommended for children up to 19 months through their second RSV season who are vulnerable to severe disease. Clesrovimab may only be prescribed in infants up to 12 months due to lack of safety data beyond this age.
There are no trials comparing the effectiveness of nirsevimab and clesreovimab. Palivizumab, which was voluntarily withdrawn from the market at the end of 2025, was only indicated for infants at high risk of RSV infection, including those with congenital heart disease, chronic respiratory disease, prematurity, immunodeficiency, and low birth weight. Contraindications to prophylactic treatment with RSV monoclonal antibodies include prior serious hypersensitivity reactions or anaphylaxis; clinicians should exercise caution in patients with coagulopathies or bleeding disorders.
An ongoing Cochrane review is studying the effectiveness of monoclonal antibodies for the prevention of RSV. A previous Cochrane review demonstrated the effectiveness of palivizumab for the prevention of hospitalization of RSV in high-risk infants. In a study in average-risk infants conducted at 235 sites in France, Germany, and the United Kingdom, the number needed to treat with nirsevimab to prevent hospitalization was 83 and to prevent severe infection due to RSV was 286. The absolute risk reduction for hospitalization and severe infection is 1.2% and 0.35%, respectively, for average-risk infants. A POEM published in American Family Physician reviewed a study of universal RSV prophylaxis in Spain, showing significant reductions in health care utilization.
There are currently no RSV monoclonal antibodies approved for use in adults; however, vaccination is available and recommended for certain populations of adults older than 50.