When reports of a mysterious pneumonialike illness first cropped up in China at the end of last year, Yutaka Tokue, head of the infectious disease and prevention division at Japan's Gunma University, knew the disease would eventually arrive in his home country.

"We need to start finding a treatment," Tokue told his colleagues.

The research team initially looked at three candidates, including an AIDS drug, that could possibly be applied to COVID-19, the disease caused by the novel coronavirus.

In the middle of February, as plans for clinical trials were being pushed forward, an unexpected patient was brought to Gunma University Hospital.

The patient had tested positive for the coronavirus on the cruise ship Diamond Princess, which was by then docked in Yokohama Port. Carrying about 3,700 passengers and crew from more than 50 countries and regions, the ship had become a hot-spot-on-sea for the new virus.

A bus arrives near the cruise ship Diamond Princess, where dozens of passengers were tested positive for coronavirus, at Daikoku Pier Cruise Terminal in Yokohama on February 16. © Reuters

"Can you use Avigan?" said a member of the patient's family, referring to an influenza drug developed by a Fujifilm Holdings affiliate.

There was talk coming out of China about Avigan's effectiveness against the coronavirus. But the efficacy had yet to be proven, and there were competing reports of the pneumonia symptoms worsening under the experimental treatment.

But with the patient in critical condition, Gunma's hospital staff decided in late February to start administering Avigan, along with other existing drugs. The virus disappeared from the patient.

Such trial-and-error approaches have been seen in hospitals and municipalities across Japan as it combats an invisible enemy that has infected more than 2,900 and killed at least 69 in the country.