Nirsevimab
Nirsevimab is a human recombinant monoclonal antibody with activity against respiratory syncytial virus, or RSV for infants. It is under development by AstraZeneca and Sanofi. Nirsevimab is designed to bind to the fusion protein on the surface of the RSV virus. Medical uses. Nirsevimab is being trialled as an experimental vaccine against respiratory syncytial virus, RSV, in the general infant population. The vaccine intends to replace existing RSV treatment palivizumab, and a single dose is enough for an infants first entire RSV season, Sanofi and AstraZeneca claim. Mechanism of action. Nirsevimab binds to the prefusion conformation of the RSV  fusion protein, i.e. it binds to the site at which the virus would attach to a cell; effectively rendering it useless. It has a modified F region, extending the half-life of the drug in order for it to last the whole RSV season. Clinical efficacy. The pivotal MELODY study is an ongoing, randomized, double-blind, placebo-controlled to evaluate the safety and efficacy of nirsevimab in late preterm and term infants. Initial results have been promising, with nirsevimab reducing LRTI (lower respiratory tract infections) by 74.5% compared to placebo in infants born at term or late preterm. Adverse effects . No major hypersensitivity reactions have been reported, and adverse events of grade 3 or higher were only reported in 8% (77 of 968) of participants in clinical trial NCT02878330. Legal status. AstraZeneca plans to file for FDA approval within the first half of 2022. If approved, it would be the first RSV vaccine to be approved since palivizumab in 1998. Research. Ongoing trials for nirsevimab are: