An anonymous reader quotes a report from Popular Science:
The Food & Drug Administration just announced that they had approved the aptly-named Xofluza, the first new antiviral drug in two decades, to help alleviate the symptoms of a flu infection. The reason Xofluza got a priority review from the FDA is that it works through a different mechanism than Tamiflu. Both are antivirals, meaning they prevent the replication of the virus, but they work at different stages in that process. First, a quick primer on how viruses infect you: a virus is basically a packet of genetic material that injects itself into a cell and hijacks the cell’s normal replication machinery, forcing it to produce millions of copies of the virus. A protein called viral neuraminidase allows those copies to exit the cell and go infect new parts of your body. Most of our effective antivirals are neuraminidase inhibitors — the virus can still replicate, but it’s prevented from escaping.
Xofluza works by preventing the viral replication in the first place. It blocks viral polymerase, an enzyme that helps make copies of the invading genetic material. This doesn’t necessarily make it better or more effective — the FDA notes that early trials suggest it’s about as effective as Tamiflu — but as the FDA Commissioner Scott Gottlieb pointed out in a press release, “Having more treatment options that work in different ways to attack the virus is important because flu viruses can become resistant to antiviral drugs.”