Nirsevimab: review of pharmacology, antiviral activity and emerging clinical experience for respiratory syncytial virus infection in infants.

Respiratory syncytial virus (RSV) is a leading cause of hospitalization and infant mortality worldwide. There are currently no approved vaccines against RSV, and immunoprophylaxis with the mAb palivizumab is limited to extremely vulnerable infants in resource-rich settings due to its high cost and the need for monthly injections throughout the RSV season. Nirsevimab (formerly MEDI8897) is a highly potent, long-acting, human, recombinant mAb that received approval for the prevention of RSV infection in newborns and infants during their first RSV season from the EMA and the UK's Medicines and Healthcare products Regulatory Agency in November 2022 based on positive results in Phase 2b and 3 clinical trials. Nirsevimab targets the highly conserved site Ø of the prefusion conformation of the RSV fusion (F) protein and contains a triple amino acid substitution in the Fc domain that extends its half-life, allowing for a single dose to cover a typical RSV season in regions with temperate climates. In this article I review key attributes of nirsevimab with an emphasis on pharmacology, pharmacokinetics, antiviral activity, and the potential for resistance and escape variants. I also summarize current progress in clinical trials and consider future research priorities.