As the worst flu season in a decade rages on, a potentially groundbreaking new drug that can kill the flu virus in just one day has won regulatory approval—in Japan.

Japanese officials granted an accelerated approval to the treatment, Xofluza from pharmaceutical maker Shionogi, last week. It could soon prove to be a significant competitor to Swiss drug giant Roche’s Tamiflu, one of the most common antivirals used to treat the flu. But it could also take until at least 2019 for Xofluza to reach the U.S. market.

Xofluza sets itself apart from Tamiflu in several key ways, according to Shionogi. For one, it requires far fewer doses—just a single pill, in fact, compared with the five-day, two-doses-per-day regimen required by Tamiflu. That could be significant given that infections tend to linger if you don’t follow through on the entire prescribed course of a medicine.

And then there’s the timeline. Xofluza was able to kill off the flu virus within 24 hours (compared with the nearly three days it takes Tamiflu to pull off the same feat) in trials. Admittedly, that rapid flu virus destruction doesn’t mean that your flu symptoms will subside just as fast; in fact, complete symptom elimination probably takes about the same time as Tamiflu does. However, symptoms begin to dissipate faster and aren’t necessarily as pronounced with Xofluza treatment, Shionogi says.

The company touts Xofluza’s unique action mechanism as the secret behind its success. Unlike other flu antivirals, Xofluza actually stops virus replication in its tracks by inhibiting an enzyme that the flu virus needs to multiply. That may sound like a major blow to Roche and Tamiflu; but the Swiss drug maker is actually allied with Shionogi, and will have the rights to commercialize the treatment in markets outside of Japan (including the U.S.) if and when it wins regulatory approval abroad.

Flu pandemics tend to put vaccines in the spotlight—especially this year, when the Centers for Disease Control (CDC) has found that the current flu vaccine is just 36% effective (and even less so against the nasty, most common strain going around, H3N2). But the development of more effective antivirals for people who have already been infected is a key element of fighting influenza, too.