The quarantine authorities are considering expanding the fourth Covid-19 vaccine shots to all people based on domestic quarantine situations and research results at home and abroad, officials said Tuesday.

"If the immunity level falls quickly, a virus resurge can also come quickly. However, we could put off the resurge depending on the immunity level," said Lim Sook-young, a senior official at the Central Disease Control Headquarters (CDCH). "I think the strategy for vaccination is very important."

In preparation for strains that may become prevalent in the second half of the year, the government will respond and prepare by focusing on how to implement vaccination, inject therapeutic agents at the right time, and develop strategies to strengthen surveillance for new variants, Lim added. The authorities confirmed a positive antibody rate of 94.9 percent through a survey but expected the immune effect to decline in the fall, making additional vaccination inevitable.

Since April 14, the quarantine authorities have provided the fourth vaccination for adults 60 and older. As of Tuesday, 34.4 percent of 12,153,926 subjects have received their fourth jab. The fourth vaccination group showed 20.3 percent higher effects in preventing infection than those who received three shots, 50.6 percent better in preventing aggravation, and 53.3 percent better in preventing death.

The CDCH stressed that over the past four weeks, 87 percent of patients with severe cases and 89 percent of deaths were over 60.

"To obtain additional protection against infection, seriousness, and death, citizens over the age of 60 should receive the fourth vaccination," CDCH said.

About the recent increase in the number of confirmed cases coming from abroad, Lim stressed that with the resumption of international flights, the number of inbound travelers is increasing.

"In proportion to the increase in inbound travelers, the number of confirmed cases imported from abroad will show an increasing trend," Lim said. "Therefore, to respond to the growing inbound cases, we require travelers to submit a negative PCR test upon entry and receive PCR within three days of entering Korea."

On Tuesday, Korea's new Covid-19 cases stayed below 10,000 for the 12 consecutive days.

Korea added 9,310 Covid-19 infections, including 76 cases from overseas, bringing the total caseload to 18,289,373, the Korea Disease Control and Prevention Agency (KDCA) said.

It reported 12 more Covid-19 deaths, raising the death toll to 24,463. The fatality rate stood at 0.13 percent.

The number of critically ill patients came to 68, down from 72 the previous day, the KDCA said.

Korea's Covid-19 cases have been trending downward since reaching an all-time high of over 620,000 in mid-March.

As of Tuesday, 44.61 million, or 86.9 percent of the population, had completed the full two-dose vaccinations, and 33.35 million, or 65 percent, had received their first booster shots.

About 4.3 million people, or 8.4 percent of the population, had gotten their second booster shots, according to the KDCA.

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