Nirsevimab (Beyfortus ® ), a long-acting intramuscular recombinant neutralising human IgG1ĸ monoclonal antibody to the prefusion conformation of the respiratory syncytial virus (RSV) F protein that has been modified with a triple amino acid substitution in the Fc region to extend the serum half-life, is being jointly developed by AstraZeneca and Sanofi for the prevention of RSV disease. The extended serum half-life allows administration of nirsevimab as a single dose to cover the RSV season. Nirsevimab was approved in the EU on 3 November 2022 and in the UK on 7 November 2022 for the prevention of RSV lower respiratory tract disease in neonates and infants during their first RSV season. This article summarizes the milestones in the development of nirsevimab leading to this first approval for the prevention of RSV disease in all infants.