Visitors wear masks at a hospital in Gwangju, Friday. Yonhap

An increasing number of investors are turning to COVID-19-themed stocks following the resurgence of infections. Experts, however, caution against making blind investments driven purely by speculation.

The stock price Woojung Bio, a firm specializes in infection control, soared right after the market opened on Monday, hitting its highest level since 2023. Its stock price has jumped 88 percent this month alone.

Other COVID-19-related stocks, such as Genematrix, also saw a sharp rise. The producer of COVID-19 testing kits saw its stock price soar over 142 percent within this month. Other testing kit makers, Seegene and Humasis, also saw their stock prices rise by over 61 percent and 71 percent, respectively, this month.

Health care firms such as Green Life Science, Celemics and Cellid also experienced respective increases of 105 percent, 140 percent and 201 percent this month.

Their sharp fluctuations led the Korea Exchange to designate Genematrix, Green Life Science and Celemics as investment warning stocks and Cellid as an investment risk stock.

A stock is designated as an investment warning stock if it experiences a sharp rise, such as a 75 percent increase over five trading days or a 150 percent increase over 20 days. If speculative trading does not calm down and the stock continues to rise even after being classified as a warning stock, it is designated as an investment risk stock, and trading will be suspended for one day.

The rebound of COVID-19 has driven increased interest in related stocks.

According to the Korea Disease Control and Prevention Agency, the number of COVID-19 hospitalizations has nearly doubled each week over the past four weeks, rising from 226 in the third week of July to 472 in the fourth week, 869 in the first week of August and 1,357 in the second week.

The surge of infection has led to related medicines and self-testing kits running out of stock.

"Sales of self-testing kit at CU convenience stores increased by 132 percent in July compared to June. From Aug. 1 to 5, sales surged by 833 percent compared to the previous month," Shinhan Securities analyst Kang Jin-hyeok said. "With the upcoming start of the school term and the Chuseok holiday, this wave of infections is expected to persist through August and into September."

Experts noted that most of the affected stocks are small- to mid-cap companies with around 100 billion won ($75 million) market capitalizations, leading to significant volatility.

Furthermore, it is uncertain whether the resurgence will translate into actual earnings growth.

Kang said, "It is important to be cautious of the heightened volatility in COVID-19-themed stocks as the spread of the virus continues to evolve."