YH009 RSV (Respiratory Syncytial Virus) is an unsegmented negative-stranded, single-stranded, enveloped RNA virus, in which the F protein is associated with the fusion of the virus envelope and the cell membrane during virus invasion. The vast majority of children become infected with RSV within the first two years of life, and in premature and young children, immunocompromised adults, and the elderly, the symptoms of respiratory infections can be more severe and potentially fatal. Palivizumab, a drug that is currently marketed, and Nirsevimab in clinical Phase Ⅲ block the fusion process between the virus and the host cell and effectively prevent the escape of mutated virus by combining with different sites of the F protein. YH009 is an effective virus-neutralizing humanized monoclonal antibody for the prevention and treatment of RSV infection in infants and young children. YH009 is currently in the CMC stage.