Two extra mutations set the stage for the seasonal influenza virus to evolve into a form that now resists three of the four drugs designed to fight it, researchers reported.
Their study, published in the journal Science, provides a way for scientists to keep an eye out for dangerous mutations in new flu viruses, including the ongoing pandemic of H1N1 swine flu.
Both can help reduce flu symptoms if taken quickly and can keep the most vulnerable patients out of the hospital, or keep them alive if they are severely ill. But two years ago the common circulating strain of seasonal H1N1 developed resistance to Tamiflu.
How the study was done