How far has the virus become resistant to neuraminidase inhibitors?
Two neuraminidase inhibitors have been widely used in the prophylaxis or treatment of pandemic (H1N1) influenza: oseltamivir (marketed as Tamiflu) and, to a lesser extent, zanamivir (Relenza). Oseltamivir-resistant pandemic strains have been detected, often associated with prolonged treatment of severe cases, but to date there is little evidence of sustained spread of these strains among untreated individuals. As the most common oseltamivir resistance mutation (an H to Y change at position 275) is close to the substrate-binding site of the neuraminidase protein, it was expected from earlier animal studies that such mutants would be less transmissible than their wild-type counterparts. There are conflicting data on this issue. For example, the H275Y oseltamivir resistance mutation emerged in seasonal (H1N1) viruses in late 2007 and spread globally during 2008 in the absence of widespread usage of the drug, suggesting that the mutation had not impaired viral transmissibility. Subsequent
