All high-risk groups should receive booster vaccination as a winter resurgence of Covid-19 is inevitable even if no new variants are leading the outbreak, Korea's top quarantine advisor said.

"In 2020 and 2021, Korea witnessed a new outbreak in December without any new variant," said Jung Ki-suck, head of the National Advisory Committee on Infectious Disease Crisis Response, during a press briefing on Monday. "Therefore, even if there are no new variants, a winter resurgence in December will be inevitable."

The reason why the epidemic repeats in winter is that individual immunity to the virus is low, and the virus is relatively more prevalent, Jung added.

Jung also noted that with the country confirming subvariants of BQ.1, including BQ.1.1, and XBB, Korea will have to wait and see which one of the subvariant will become a dominant strain in December.

During the briefing, Jung emphasized the need for vaccinations for high-risk groups, especially in preparation for the new viral wave.

"To reduce the overall epidemic scale, booster vaccination is essential," Jung said. "However, reservations for the improved booster vaccination remain low."

Unlike in the past, all high-risk groups should receive booster vaccination in a situation where the virus has a high transmission rate, Jung added.

Jung stressed that among those over 60, only 35 percent of the total have immunity toward the virus through booster vaccines or infections.

"The remaining 65 percent will be vulnerable to the virus, if they don't get the booster vaccination," Jung said. "Vaccination in high-risk groups is essential because the fatality rate increases with age."

There is no such thing as herd immunity as the Covid-19 virus is currently spreading similar to that of the flu, Jung added.

Notably, Jung stressed that the winter vaccination rate at facilities vulnerable to infection, which accounts for 33 percent of the deaths, is particularly low at 6 percent.

"Each local government should step in and persuade and guide those included in the high-risk group so that they can receive the vaccine," Jung said.

On Monday, Korea added 18,671 new Covid-19 infections, including 60 cases from abroad, bringing the total caseload to 25,856,910, according to the KDCA.

The nation also reported 18 more Covid-19 deaths, raising the death toll to 29,390. The fatality rate stood at 0.11 percent. The number of critically ill patients came to 365, up 19 from the previous day.

According to the KDCA, about 44.69 million among 52 million Koreans have been fully vaccinated. In addition, about 33.66 million people had received their first booster shots, and 7.55 million had their second booster shots.