Influenza A virus-IN-8 (S5) is a macrocyclic peptide with no cytotoxic. Influenza A virus-IN-8 is also a potent Influenza A Virus (IAV) inhibitor (with sufficient protease stability) with IC 50 s of 6.7 and 6.6 nM for H1 and H5 variants, respectively. Influenza A virus-IN-8 shows good affinitiescan to H1 variants, binds to a conserved region in the HA stem with a K d of 1.0 nM.