the fi6 provides scientists with a broadly neutralizing antibody that recognizes all 16 ha subtypes, including emerging ones, such as h5n1. but, because the replication of the influenza virus is somewhat error-prone, the virus evolves as a quasispecies, and widespread use of antiviral drugs can lead to resistant strains. such has been the case for oseltamivir and for the m2 ion channel blocker amantadine. therefore, before considering fi6 as long-term prophylactic or therapeutic agent against seasonal influenza, we would first have to determine whether the influenza virus could quickly mutate the epitope targeted by fi6 and escape recognition by fi6 after exposure.