Nirsevimab is a monoclonal antibody with activity against Respiratory Syncytial Virus (RSV). Monoclonal antibodies are laboratory-made proteins that mimic the immune system’s ability to fight off harmful pathogens such as viruses. One dose of nirsevimab administered to infants as a single intramuscular injection prior to, or during RSV season, may provide protection during the RSV season. Infants have the highest incidence of severe disease, peaking at 1–3 months of age.