Experts cast doubt over claims by officials in the city of Osaka that a gargling medicine could help treat coronavirus patients, even as shelves across Japan were stripped clean of popular brands.

There’s not enough evidence to support Gov. Hirofumi Yoshimura’s claim that gargling with diluted povidone-iodine could prevent mild coronavirus patients from falling seriously ill, Toshio Nakagawa, chairman of the Japan Medical Association, told reporters Wednesday. The World Health Organization Center for Health Development also added to skepticism.

"I understand that the governor must be very concerned about the sudden growth of cases in his region and is looking for some positive news,” said Nakagawa. "I don’t intend to attack the claim as being inappropriate, but the position of our organization is that we should keep calm and research it.”

Yoshimura said at a briefing Tuesday that a study in Osaka had found gargling with diluted povidone-iodine four times a day reduced those testing positive in a group of 41 patients to just 9.5 percent after four days, compared with 40 percent for a group who gargled with just water. That announcement spurred panic buying of popular brands across the country, sending shares in producers and distributors soaring. They gave back most of those gains Wednesday.

The World Health Organization Center for Health Development seemed to take a swipe at the claim in an infographic on its Twitter account Wednesday. "There’s no scientific evidence that gargling medicine prevents the coronavirus,” it said.

"I never said a single word about it having a preventative effect,” Yoshimura told reporters Wednesday, saying the media needed to responsibly report the facts. He added that he was extremely skeptical about the treatment at first.

"But looking at the results, looking at those clear numbers — for a drug that’s accessible to everyone” and can bring patients closer to recovery, "it sounded like something that should be a lie, but it’s true,” he said, while calling for people to avoid bulk-buying the formula.

The excitement and confusion over Yoshimura’s announcement highlights the difficulty faced by the scientific community and politicians alike in dealing with the novel coronavirus. As late as April, the WHO said that healthy people didn’t need to wear face masks, a stance the body has now moderated. There has been debate over different treatments hailed as treatments for the virus, from hydroxychloroquine to Fujifilm Holdings Corp.’s antiviral drug Avigan.

Povidone-iodine is an antiseptic more commonly known as betadine. In Japan, it’s sold as gargle by Shionogi & Co., using the name Isojin under license from Mundipharma, as well as by Meiji Holdings Co. Shares in Meiji fell 3.8 percent in Tokyo, giving up almost all the gains from yesterday.

People in Japan commonly gargle as a preventative measure against colds and flus in winter, similar to hand-washing, though its effectiveness is still a matter of dispute. A 2005 study by Japanese scientists concluded gargling with water helped prevent upper respiratory tract infections, but didn’t find using povidone-iodine any more effective than water, though a much smaller study on just 23 patients in 2003 did.

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