This is a humanized IgG1 antibody using the same sequences as the therapeutic antibody nirsevimab. It is a monoclonal antibody with activity against the respiratory syncytial virus (RSV) fusion protein. RSV is a major cause of lower respiratory tract infection and hospitalization in infants. Nirsevimab is designed to bind the F1 and F2 subunits on the RSV’s surface at a highly conserved epitope and locks the RSV F protein in the prefusion conformation to block viral entry into the host cell. It has a modified Fc region, extending the half-life of the drug in order to last the whole RSV season.