Health officials said that Korea has confirmed the first case of XL, a recombinant of the Omicron Covid-19 strain.
A recombinant variant occurs when an individual simultaneously becomes infected with two or more variants. The XL is one of 17 recombinant variants involving the BA.1 and BA.2 Omicron strains.
According to the World Health Organization (WHO), the U.K. has confirmed 66 cases of XL since it first discovered the variant in February. Korea has become the second country to confirm the XL strain with the most recent case.
According to the Central Disaster and Safety Countermeasures Headquarters (CDSCH), the person infected with the XL subvariant is a man in his 40s who tested positive for the virus in South Jeolla Province on March 23. Health officials explained that the patient had completed the third vaccination, showed no symptoms, and had not traveled to foreign countries recently.
"The patient had received the vaccine and has now completed mandatory quarantine," said Lee Sang-won, head of the epidemiological investigation and analysis team at CDSCH. "There were no special abnormalities during quarantine treatment."
Lee noted it is unclear whether this mutation occurred in Korea or came from abroad.
"The nucleotide sequence is almost identical to the nucleotide sequence found from the XL strain found in the UK," Lee said. "Therefore, the possibility that the variant came in from overseas is high."
The quarantine authorities confirmed that there was an XL mutation case in Korea after conducting random genetic analysis tests on 3,438 samples of confirmed patients in the past month. The authorities are investigating about 80 people, including family members and contacts of the infected person, for XL mutation infection.
In Korea, the existing Omicron (BA.1) and BA.2 (Stealth Omicron), a sub-family of Omicron, are trending simultaneously. Last week, the detection rate of BA.2 overtook BA.1 as the dominant specie in Korea after accounting for 85.2 percent of local cases and 75 percent of imported cases.
Experts have expressed concerns about the possibility of recombination mutation as the two mutations BA.1 and BA.2 are prevalent simultaneously. However, the recent case is the first time Korea has confirmed a recombination mutation.
"Although many Omicron mutations occurred in a short period in Korea, the rate of recombination mutations naturally found in Korea is low despite authorities monitoring many cases," Lee said. "Recombinant mutation is a phenomenon in which genes are mixed when two types of viruses are infected together in a cell."
However, Lee predicted that the occurrence of the new variant would not affect the government's plans to ease distance measures.
"The newly discovered mutation is not classified as an important mutation, and the government expects that it will not affect the current trend of decreasing prevalence," Lee said. "I think it will have a limited impact on the current quarantine system and social distancing rules."
The Korea Disease Control and Prevention Agency (KDCA) confirmed 210,755 new virus cases, the cumulative caseload to 15,635,274.
Critically ill patients stood at 1,005, down 94 from the previous day. An additional 171 people died of Covid-19, lifting the death toll to 19,850, with a fatality rate of 0.12 percent.
As of Thursday, 32.94 million people have received booster shots, or 64.2 percent of the country's population. The number of fully vaccinated people also came to 44.52 million, representing 86.7 percent of Koreans, the KDCA said.
Korea's virus cases have been on the decrease after peaking in mid-March. On Monday, new cases fell to 90,928, marking the first drop to five digits since the Feb. 22 count of 99,562.
Health authorities are expected to announce a new "post-Omicron scheme" later this week, further lifting social distancing and allowing people to go mask-free outside from June or July.