Few doctors even test patients for flu, and Tamiflu is not widely prescribed. But the news is sobering because the pill, known generically as oseltamivir, is one of the few weapons against influenza, which kills an estimated 36,000 people in the United States in an average year. It is also considered a key weapon against a potential pandemic of a new type of influenza, and this study suggests the virus can rapidly evade its effects. This season, nine children have died from influenza, most apparently healthy before they got infected, the CDC reports.