When Shionogi got Japanese approval for its novel flu drug Xofluza (baloxavir marboxil) in February, it didn’t expect a U.S. decision in 2018. Now, an FDA priority review has made it possible for its partner Roche to get a go-ahead before New Year's.

Roche’s Genentech announced Monday that the FDA has agreed to make a decision on possibly the U.S.’ first one-time, single-dose flu drug by Dec. 24, 2018. If approved, baloxavir marboxil would also be the first flu medicine with a novel mechanism of action in nearly 20 years, said Sandra Horning, M.D., Genentech’s chief medical officer and head of global product development, in a statement. A Genentech spokeswoman told FiercePharma it’s still early to comment on the U.S. brand name for the medicine.

Xofluza acts at a different stage in the virus replication than other currently available anti-flu treatments. It is designed to inhibit the cap-dependent endonuclease protein, which flu viruses rely upon to replicate in the human body. The FDA designation is likely based on its novel mechanism and great potential shown in a phase 3 study.

Xofluza is given only once, instead of five days at twice-daily dosing required by Roche’s own flu stalwart Tamiflu. And, with just that one pill, the drug managed to relieve symptoms and bring down fever in time on par with Tamiflu, a 1,436-subject phase 3 showed.

What’s more important, the drug can suppress the flu virus level in just 24 hours, while it takes Tamiflu 72 hours to do the same. Besides, it could treat some Tamiflu-resistant strains from avian flu viruses H5N1 and H7N9.

Furthermore, its quick virus-killing action could stop the virus from spreading to others sooner, and packing such power in a one-time regimen could also mean convenience for patients.

Gottlieb himself has also indirectly given Xofluza some credit recently. When asked by lawmakers about it at a congressional subcommittee hearing on flu preparedness in March the FDA chief said: "I think the bottom-line message is that we are very interested in having a spectrum of antiviral drugs that act differently, at different points in the virus. In case the virus itself becomes resistant to one approach at targeting the virus, we have backups and we have alternative approaches."

Roche is currently seeking approval to treat uncomplicated influenza in people 12 years and older. It will soon report findings from a completed phase 3 in patients with influenza at high risk of complications. Besides seniors aged 65 or above in general, people who have some existing medical conditions like chronic lung disease, compromised immune system, blood disorders, heart diseases, among others, are considered by the CDC as being at high risk of influenza complications.

The FDA priority review came right after the U.S. went through a severe flu season that led to record-breaking outpatient and hospitalization cases, with widespread flu activity across the country for a long period. For the seven months from October to April, over 30,000 confirmed influenza-related hospitalizations were reported to the CDC, according to the agency’s recent report.

Genentech obtained commercial rights to Xofluza outside of Japan and Taiwan, China through a licensing deal with developer Shionogi in 2016 as Tamiflu sales cratered. In 2017, sales of Tamiflu dropped a third to CHF 535 million ($540 million), but the severity of the past flu season has given it a rare 11% lift in the first quarter, to CHF 292 million ($295 million). During Roche’s first-quarter earnings call, pharmaceuticals division chief Dan O’Day said Xofluza "has the potential to become a full replacement for Tamiflu."