Shares of Namyang Dairy Products, one of South Korea’s major dairy firms, soared in intraday trading on Wednesday as the company claimed that its own yogurt lineup Bulgaris can reduce the infection risk of COVID-19.

The dairy company’s shares once spiked up 28.68 percent to 489,000 won ($437.39) in the early morning trading session, but plunged 5.13 percent to close at 360,500 won.

Within some 20 minutes after the opening bell, its preferred stocks also shot up by a daily permissible limit of 29.78 percent to reach 231,000 won. The shares, however, shed 6.18 percent, at the closing bell.

While Namyang Dairy’s claim came a day earlier, some market watchers suspect some investors may have used undisclosed information ahead of the announcement, leading to the company’s recent stock surge. Financial authorities are also keeping a close eye on the firm’s stock movements.

Prices of Namyang Dairy and its preferred stocks saw a sudden, sharp rise from Friday’s trading session.

Shares of Namyang Dairy advanced 7.19 percent and 6.71 percent on Friday and Monday, respectively. It again soared 8.57 percent in Tuesday’s trading. The preferred stocks also gained 6.67 percent on Friday and an additional 1.14 percent on Monday.

At a conference held in Seoul, Park Jong-su, the head of antiviral immune research center under Namyang Dairy, said, “We’re the first firm in the country that has discovered fermented dairy products are effective in preventing influenza and COVID-19 viruses.”

“Our experiments showed that Bulgaris helped remove the Influenza A (H1N1) virus at a 99.999 percent rate of success, and the COVID-19 at a 77.8 percent success rate,” the researcher said, adding the coronavirus effectiveness test was conducted using monkey’s lung cells.

Following the dairy company’s claim, people rushed to buy the yogurt products at local retail stores. The country’s public health authorities, however, voiced concern over Namyang Dairy’s unexpected announcement.

“The latest research result has not proved to be effective in eliminating those viruses in human body. Therefore, it is hard to say whether it can serve as an actual prevention or treatment measure for (the viruses),” the Korea Disease Control and Prevention Agency said.

By Jie Ye-eun (yeeun@heraldcorp.com)