A single-dose pill that can halt the flu virus within a day.

That's what Japanese drug maker Shionogi claims its new flu treatment can do, the Wall Street Journal reports, but the compound that could relieve one of the worst flu seasons in years wouldn't hit U.S. shelves until at least 2019.

It took a median time of 24 hours for Shionogi's experimental compound to kill the flu in American and Japanese patients during a late-stage trial, per the Journal, faster than any flu drug available. And it requires just a single dosage.

Compare that to Tamiflu, the popular anti-flu drug that requires twice-a-day doses for five days. In the above trial, Tamiflu took three times longer to kill the virus.

Little surprise, then, that Roche — the Swiss company behind Tamiflu — came onboard to help develop the drug, Bloomberg reports.

The current flu season is putting Americans in hospitals and emergency rooms at levels not unlike the 2009 swine flu, experts said, with reports of otherwise healthy people dying from the infection.

Hence the rush of companies to respond with next-level iterations of anti-viral treatments: Johnson & Jonhnson is working on a drug that blocks many flu viruses' genetic material from replicating, Bloomberg notes, while its development of the "holy grail" — a universal flu vaccine that would prevent the need for new vaccines each year — remains further off.

Shionogi's single-day drug has been fast-tracked for approval in Japan and could get approval there next month, the company told the Journal, but it won't submit for U.S. approval until this summer.

Flu treatments on the market like Tamiflu remain few and far between. Yet the flu vaccine is only about 30% effective against the flu's most common strain this year, according to the CDC.

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