The Food and Drug Administration has approved Xofluza, the first new antiviral flu treatment in nearly 20 years.

Genentech's Xofluza, baloxavir marboxil, is meant to treat acute uncomplicated influenza in patients 12 years and older who have had symptoms for no more than 48 hours. Genentech is a unit of Roche, which produces Tamiflu, a commonly used flu treatment.

The single-dose treatment will be available across the U.S. in the coming weeks, a Genentech spokesman told CNBC. It will cost $150 but may be available to some patients with commercial insurance for $30, he added.

Last year was a particularly nasty flu season: More than 80,000 people died and more than 900,000 were hospitalized, according to the Centers for Disease Control and Prevention.