palivizumab + nirsevimab

**Palivizumab + nirsevimab** is a combination of two monoclonal antibodies used for respiratory syncytial virus (RSV) prophylaxis in infants. Palivizumab (Synagis), a humanized monoclonal antibody, binds to the RSV fusion (F) protein on antigenic site II to inhibit viral fusion and replication, primarily indicated for high-risk preterm infants, those with chronic lung disease, or congenital heart disease via monthly intramuscular injections during RSV season. Nirsevimab (Beyfortus), a recombinant human IgG1κ monoclonal antibody with an extended half-life due to Fc modifications (YTE substitution), targets a conserved epitope on the prefusion RSV F protein (antigenic site Ø) to block membrane fusion, neutralizing RSV A and B strains; it is administered as a single intramuscular dose for broader use in all infants entering their first RSV season and certain high-risk children in their second season. Developed by AstraZeneca/MedImmune (palivizumab) and Sanofi/AstraZeneca (nirsevimab), both provide passive immunity to reduce RSV lower respiratory tract infections and hospitalizations, with nirsevimab offering longer protection and similar efficacy/safety to palivizumab in comparative data.[1][2][3]