A state research organ said Thursday that there would be no resurging of new Covid-19 cases in the short term even if the government lifts the mandatory quarantine of confirmed patients.

The National Institute of Mathematical Sciences concluded so quoting a study conducted by Professor Jeong Eun-ok of Konkuk University and his team, based on a mathematical modeling analysis considering the transmission power and the effect of vaccination.

According to the research, even in the worst-case scenario, new virus cases will reach 36,621 after one week of lifting the mandatory quarantine and 55,937 after four weeks. Severe cases will be 271 after one week and 459 after four weeks. Suppose Korea maintains the current transmission level and the mandatory quarantine of confirmed cases. In that case, it will see 26,002 new cases after one week and 20,525 cases after four weeks.

"New virus cases will not resurge in the short term even considering Omicron subvariants," Professor Jeong said. "This shows the importance of refraining from gatherings of confirmed patients and observing quarantine rules." However, a simulation that presumes Omicron subvariants become dominant strains points to a virus resurge this summer.

The authorities will announce post-pandemic plans, including whether to lift the seven-day quarantine mandate for confirmed Covid-19 patients, on Friday.

Korea has eased most Covid-19 rules, including the cap on private gathering sizes and business hours, as the virus curve began to head down amid high vaccination rates.

Meanwhile, according to a U.S. study, unvaccinated people infected with the Omicron variant have very little immunity against other variants of the virus that causes Covid-19.

"As Omicron is so infective, we were hoping that it would help bring us closer to herd immunity," said Dr. Melanie Ott, a virologist at the Gladstone Institutes in San Francisco and lead author of the paper.

Instead, Dr. Ott's team found that people infected with Omicron only get protection against infections from Omicron subvariants, not from other variants, such as Alpha, Beta, Delta, and Gamma.

Dr. Ott's research showed the importance of vaccination as vaccinated people have a chance to gain "super immunity."

"People who received vaccination but had breakthrough infection with Omicron or Delta showed protection against all variants," the expert said. "Considering the possibility of re-infection, we believe that vaccination is better than natural immunity caused by Omicron."

However, booster vaccination for older adults is progressing very slowly here.

According to the Korea Disease Control and Prevention Agency (KDCA), only 29.8 percent of the 11.81 million adults 60 and older have completed their second booster shot.

The government started administering the fourth dose of the Covid-19 vaccine to older adults who had received the third vaccination at least four months ago on April 14.

The agency reemphasized the need for a second booster shot. About 87 percent of patients with severe cases and 94 percent of deaths have come from people over 60.

"Despite the spread of Omicron, vaccination is still the most effective and important means to protect everyone's health," the KDCA said. "Notably, the second booster shot is necessary to prevent severe cases and death among the elderly."

Therefore, the agency urges the elderly and their families to participate in receiving booster shots, it added.

On Thursday, the KDCA confirmed 28,130 new virus cases, raising the cumulative caseload to 17,889,849.

The death toll came to 23,842, up 40 from the previous day, with a fatality rate of 0.13 percent. However, critically ill patients came to 374, down 39 from a day earlier.

According to the KDCA, about 44.56 million people have been fully vaccinated, or 86.8 percent of 52-million Koreans. In addition, about 33.24 million people had received their first booster shots, representing 64.8 percent.