The first new influenza drug in 20 years was approved in October, and maker Genentech says Xofluza began reaching pharmacies recently — good timing for flu season.

With a single pill, Xofluza can shorten the fevers, chills, sore throat and other symptoms that make a bout of the flu so miserable.

That’s not to suggest Xofluza is magical. It has limitations, just like Tamiflu, the well-known antiviral that has been around for 20 years. Experts still urge that you get the flu vaccine to reduce your chance of infection.

But as U.S. Food and Drug Administration Commissioner Scott Gottlieb said in announcing its approval, Xofluza “provides an important, additional treatment option.”

Here are things to consider about that option — and the flu.

A mutating target. Last flu season was the worst in decades, sickening 49 million people and killing 79,000. The dominant virus strain mutated and undercut the effectiveness of the vaccine, which is made each year to try to match circulating strains. On top of that, far fewer people got flu shots. It isn’t yet clear how bad this season will be, but so far, federal surveillance shows little or no flu activity in most states, including Pennsylvania and New Jersey.

The window of opportunity. Xofluza (baloxavir marboxil) works by preventing the virus from copying itself, while Tamiflu (oseltamivir phosphate) and two similar drugs keep the virus from spreading within the body. Either way, antivirals should be given within 48 hours of the first symptoms to be effective. Ebbing Lautenbach, chief of infectious diseases at the University of Pennsylvania, said the flu usually hits hard and suddenly — unlike, say, a cold. “But it still requires a patient to feel lousy and then fairly quickly contact their provider,” he said. “If you’re outside the 48-hour window, there’s not much to be gained” from an antiviral.

Flu symptoms typically last from five to seven days. In the two clinical trials that led to approval, Xofluza provided relief more quickly than a placebo — by 26 hours. Xofluza and Tamiflu were similar in shortening suffering. As for side effects, Xofluza had no more than a placebo.