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Preschool students and their family members are tested for COVID-19 at a drive-thru screening clinic in Gwangju on July 6. (Yonhap News)

A large portion of the novel coronavirus cases currently being diagnosed in South Korea belong to the GH strain, a study shows. This means that the recent outbreak has been driven chiefly by the GH strain prevalent in the US and Europe, rather than the S strain introduced from the Chinese city of Wuhan between February and March or the V strain found in the Shincheonji Church outbreak in Daegu. Research findings indicating that the GH strain is a mutated form of the G strain that is even more infectious have prompted a debate among scholars. Mutations in the virus have been cited as a factor in the sharp rise in the number of patients in places such as the US and Europe.

On July 6, the Korea Centers for Disease Control and Prevention (KCDC) announced that an analysis of the genome base sequences of 526 examples of the virus detected in South Korean patients showed 333 of them, or 63.3%, to belong to the GH strain. Numerous recent cluster infections -- including those connected with Gwangneuk Temple and the Geumyang Building in Gwangju, a door-to-door sales business and Dreaming Church in Daejeon, clubs in Seoul’s Itaewon district, the door-to-door sales business Richway, a table tennis gymnasium in Seoul’s Yangcheon District, Protestant churches in Seoul Capital Area (SCA), and a Coupang logistics center -- were all associated with this strain.

The World Health Organization (WHO) previously categorized the virus into three main varieties -- S, V, and G -- based on analyses of its genetic base sequence. The S and V strains were found chiefly in China and other Asian countries at the time of the coronavirus pandemic’s start early this year. The G strain, which has spread primarily in Europe, North America, and Africa, has been subdivided in turn into G, GR, and GH strains. A total of 33 South Korean cases were associated with the S strain, including those found among overseas Koreans in Wuhan and at a call center in Seoul’s Guro District, while 127 were associated with the V strain, including cases found at the Shincheonji Church in Daegu, Cheongdo Daenam Hospital in North Gyeongsang Province, Onchun Presbyterian Church in Busan, and a Zumba dance workshop in Cheonan. The GR strain has been newly discovered among some individuals arriving from overseas, including crew members on a Russian cargo ship.

“Our analysis is that the recent outbreak has been driven by virus [strains] introduced by individuals arriving from Europe and the US between March and April,” said KCDC Director Jung Eun-kyeong.

“We believe the S and V strains that circulated in February and March have been for the most part contained,” she added.

Research published in the science journal “Cell” and elsewhere recently caused a stir with its reports that a mutation (G614) within the G strain of the virus allows it to infect cells more easily, with cell proliferation levels 2.6 to 9.3 times higher than the previous D614 variety. Jung said, “Globally, it is the GH strain of the virus that has been predominantly spreading, and this strain is believed to have a high level of transmissibility due to its ability to proliferate within cells and attach to infected portions of human cells.”

“Changes in the infectiousness due to the virus’s mutation will need to be confirmed through additional research,” she cautioned.

As of midnight on July 6, the number of patients newly diagnosed with the virus stood at 48 that day, including seven in Gwangju. Twenty-four of the cases involved community transmissions. The risk of transmission has been growing in particular in regions outside of the SCA, including Gwangju and South Jeolla Province. The KCDC reported a reproduction number (R value) of 1.34 for Chungcheong and Jeolla Provinces over the past week -- higher than the national average of 1.06. Representing the average number of people infected by a single patient, the R value is used as an indicator to determine the rate of the virus’s transmission as well as the speed of the epidemiological research.

The possibility of the virus’s airborne transmission is also drawing renewed attention. A day earlier, 239 scientists in 32 countries published an open letter referring to the risks of airborne transmission of the virus and urging the WHO to revise its prevention guidelines. The WHO has stated that the virus is transmitted through mixture with saliva droplets. At sizes of just over 5 micrometers, the droplets do not travel far. For airborne transmission to occur would require small droplet nuclei of 5 micrometers or less or a small aerosol state of around 1 micrometer.

“Within sealed and enclosed small spaces, small droplets can float for a long time in the air, contaminating the air indoors and raising the risk of transmission,” Jung said, stressing the importance of wearing masks in indoor settings.

By Hwang Ye-rang and Lee Keun-young, staff reporters

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