Resistance to zanamivir has been low for both seasonal and pandemic viruses compare to oseltamivir. Molecular structure of zanamivir has a guanidino group, this group interacts with the E119 residue in the active center pocket. Resistance to zanamivir can be because of mutations that effect binding affinity between the enzyme and the inhibitor. Mutation at the E119 residue has been shown to reduce the inhibitors efficiency in vitro.