Older antivirals don't work on this years' strain of flu.

From the CDC : While the primary strategy for preventing complications of influenza infections is annual vaccination, antiviral medications with activity against influenza viruses can be effective for the prophylaxis and treatment of influenza. Two classes of antivirals are currently available—the M2 ion channel inhibitors (i.e., the two adamantanes amantadine and rimantadine) and the neuraminidase inhibitors (i.e., oseltamivir and zanamivir). The neuraminidase inhibitors are effective for the treatment and prophylaxis of influenza A and B, while the adamantanes are only active against influenza A viruses. This alert provides new information about the resistance of influenza viruses currently circulating in the United States to the adamantanes, and it makes an interim recommendation that these drugs not be used during the 2005–06 influenza season.