Prime Minister Shinzo Abe has enthusiastically promoted the anti-influenza drug Avigan as a possible game-changer in the fight against the coronavirus, but medical experts have called for caution, citing its side effects and unproven efficacy.

"Avigan has already been administered in more than 120 cases and we are receiving reports that it is effective in alleviating symptoms of the novel coronavirus," Abe told a news conference on April 7, referring to the drug, developed by a group firm of Fujifilm Holdings Corp., that is currently undergoing clinical tests on coronavirus patients.

"We intend to expand to the greatest possible extent its administration to patients wishing to take it. ...To make that possible, we will increase our stockpile of Avigan to three times the current level, enough to treat 2 million people," the prime minister said.