Pandemic H1N1 2009 influenza virus with the H275Y oseltamivir resistance neuraminidase mutation shows a small compromise in enzyme activity and viral fitness

The neuraminidase protein of pandemic influenza isolates tolerates the H275Y mutation and this mutation confers resistance to oseltamivir. However, unlike seasonal H1N1 viruses isolated since 2007, the mutation is not associated with any fitness advantage and thus is unlikely to predominate without further antigenic drift, compensating mutations or intense selection pressure.