The Food and Drug Administration has approved a new drug that kills the flu in just one day!

Genentech's Xofluza is the first new antiviral flu treatment in nearly 20 years. It inhibits something called the cap-dependent endonuclease protein, which the virus needs to make more copies of itself.

The drug is meant to treat acute uncomplicated influenza in patients 12 years and older who have had symptoms for no more than 48 hours.

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.

This is not a replacement for the flu vaccine. The CDC recommends getting vaccinated by the end of October.

The past flu season was an especially deadly one, with 80,000 deaths and more than 900,000 people ending up in the hospital.

The flu attacks the lungs, nose, and throat. Young children, older adults, pregnant women, and people with chronic disease or weak immune systems are at high risk. Symptoms include fever, chills, muscle aches, cough, congestion, runny nose, headaches, and fatigue.