South Korea begins inoculation using bivalent COVID-19 vaccines from Tuesday, the country's health authorities said on Monday.

According to the Korea Disease Control and Prevention Agency, Moderna's bivalent COVID-19 vaccine will be used for the first time as a booster in the country. The bivalent COVID-19 vaccine developed by Pfizer will be used after completion of the regulatory process.

The bivalent COVID-19 vaccine will be first available for people at high risk and in other vulnerable groups, including those aged 60 and above, as well as workers and patients at facilities that are vulnerable to infections, the KDCA said.

The number of people who made reservations in high-risk groups reached 295,040 as of Friday, the KDCA added.

Adults 18 to 60 can also reserve leftover bivalent COVID-19 vaccines on a daily basis if they have completed their primary series vaccination. They can make reservations for the bivalent vaccines by checking directly with local hospitals or through mobile applications. Reservations through mobile application, however, start at 4 p.m. Wednesday.

All people who are trying to receive the bivalent COVID-19 vaccines should wait 120 days since their last vaccine, the KDCA noted. Anyone who has contracted COVID-19 must also wait 120 days from their infection before receiving the boosters.

“Booster shots are very important to prevent a resurgence of COVID-19 during the winter season and a potential COVID-19 and influenza 'twindemic,'” said Peck Kyong-ran, commissioner at the KDCA. She added that the country’s health authorities recommend people to receive the bivalent vaccines as boosters, which are believed to be more effective than existing COVID-19 vaccines.

The government's recent efforts to increase the COVID-19 booster rate comes amid the growing possibility of a COVID-19 and influenza "twindemic."

According to the KDCA, more people have recently shown flu-like symptoms. The health agency’s report last week said that an average of 7.1 people out of 1,000 who visited a doctor showed flu-like symptoms between Sept. 25 and Oct. 1.

That was a 44.9 percent increase from the previous week, when an average of 4.9 people had flu-like symptoms. It was also the highest since 2014, when the government started to compile related data.

The KDCA said the rate has reached an alarming level, given that an average of 3 or 4 people out of 1,000 usually report flu-like symptoms around this time of year.

Over the past two years, South Korea was able to largely escape the spread of seasonal influenza mainly due to strict social distancing rules and mask mandates. But this year, the country is witnessing increases in people showing flu-like symptoms as the government has lifted major social distancing measures.

Doctors and health authorities are currently on guard as an increase in influenza cases could coincide with the COVID-19 pandemic, which has not receded yet.

Korea’s flu season normally starts in November and goes through April.

Meanwhile, the country reported 8,981 new COVID-19 infections during the 24 hours of Sunday, decreasing from the previous day's 17,654. The decrease was mainly due to fewer tests administered over the weekend.