On Thursday, quarantine officials detected the first case of BA.2.75, dubbed “Centarus,” the most contagious Omicron subvariant with greater immune-avoidance properties than BA.5.
BA.2.75, first sequenced in India in May, has been found in about 10 countries, including the U.S., Australia, and Germany. According to health officials, BA.2.75 has many mutations in the spike protein compared to previous subvariants, making the virus bind to cells more effectively and evade antibodies formed by vaccines or infections.
The confirmed patient is a 60-year-old man living in Incheon, south of Seoul, with no overseas travel history.
Quarantine officials have included the patient in the general management group, meaning he will have to undergo a seven-day mandatory self-quarantine like other Covid-19 patients. The authorities added that they are conducting an in-depth investigation into the route of infection of the patient.
The first suspected case of BA.2.75 comes amid mounting concerns that the BA.5 subvariant may soon become a dominant strain in Korea.
Officials noted that BA.5's share in total infections rose to 35 percent last week from 28.2 percent a week earlier.
Korea's daily Covid-19 tally also maintained a "weekly doubling phenomenon" to nearly 40,000 on Thursday.
The nation added 39,196 Covid-19 infections on Thursday, bringing the total caseload to 18,641,278, the Korea Disease Control and Prevention Agency said.
Statistics experts predicted that if the spread of the virus becomes more severe and the reproductive rate of how many people contract the virus from one infected person increases by more than 30 percent, the number of new confirmed cases per day will rise close to 300,000 after four weeks.
In response to the resurgence, the government has expanded eligibility for second booster shots to all people 50 and older and those 18 and older with underlying health conditions.
President Yoon Suk-yeol appealed to the public to actively participate in the second booster vaccination after receiving his fourth shot on Wednesday.
The government will maintain seven-day mandatory isolation for people infected with the virus and keep the indoor mask-wearing mandate in place.
However, health officials said they would not reinstate a tight social distancing scheme. The former Moon Jae-in administration implemented a strict distancing system, including the night business curfew for service providers and bans on gatherings, eating indoors in addition to compulsory outdoor masks during previous viral outbreaks.
The presidential office stressed that the basic philosophy of the quarantine policy under the Yoon administration is different from the previous government as it is centered on autonomy and personal responsibility rather than sacrifice or coercion.
"If the previous government forced self-employed citizens to make sacrifices through business hours and to gather restrictions and strict social distancing rules, our government wants to implement a sustainable quarantine policy based on citizens' autonomy and responsibility," a presidential office official said. "When we speak of science-based quarantine measures, we are not talking about policy outcomes."
The official stressed that the government is using the term to emphasize the process and system, in which experts directly participate in decision-making based on scientific evidence and data.
"Therefore, the government has formed the Advisory Committee on Infectious Disease Risk Management, and it is important to create a system so that experts' opinions can be reflected in policies," he added.
The official responded to widespread public criticisms questioning the substance of the Yoon administration’s “scientific quarantine” aside from the president’s calls for additional vaccination.
As of Thursday, 44.63 million, or 87 percent of the population, had completed the full two-dose vaccinations, and 33.39 million, or 65.1 percent, had received their first booster shots.
About 4.58 million people, or 8.7 percent of the population, had gotten their second booster shots, according to the KDCA.