Korea’s new Covid-19 cases fell Thursday after reaching a four-month record high the previous day. Still, new deaths and severe cases climbed to a three-month high amid the spread of highly contagious Omicron subvariants.

The country added 137,241 new Covid-19 infections, bringing the total caseload to 20,983,169, the Korea Disease Control and Prevention Agency (KDCA) said. Of the new cases, 522 were from overseas.

Thursday's tally fell from 151,792 Wednesday but surged compared to 107,859 a week earlier.

Imported cases have risen recently, with such infections hitting a record high of 615 Wednesday. Imported cases stayed over the 400s this month. Daily Covid-19 cases have trended downward after peaking at around 620,000 in mid-March. However, infections have spiked again due to increased movement and public gatherings since authorities lifted almost all anti-pandemic curbs in April.

The number of seriously ill patients also increased to 418, up from 402 on Wednesday. The tally was the largest in three months. The KDCA reported 59 Covid-19 deaths, the highest since May 12, raising the death toll to 25,441. About 90 percent of the new deaths came from high-risk groups, including people aged 60 and older and those with underlying health conditions.

The fatality rate was 0.12 percent.

As of Thursday, 44.66 million, or 87 percent of the country's population, had received full two-dose vaccinations, and 33.5 million, or 65.3 percent, had received their first booster shots. About 6.4 million people, or 12.5 percent of the population, had gotten their second booster shots, the KDCA said.

Pointing to the low vaccination rate of people with underlying diseases despite their high mortality rate after infections, the quarantine authorities called for them to get a second booster shot.

Officials cited the analysis of the Korea Health Insurance Service, noting that 76 percent of cancer patients and 71 percent of diabetics aged 20 and older have failed to receive the second booster shot.

They also explained that circulatory system diseases, such as cerebral infarction, heart failure, and neurotic disease, including dementia, were confirmed as underlying diseases among people who died of Covid-19.

The U.S. Center for Disease Control also said 94.9 percent of hospitalized people because of Covid-19 had at least one underlying disease. According to the CDC, people with underlying diseases are 1.53 times more likely to die from Covid-19 than those without them and1.3 times more likely to receive treatments at intensive care units.

The officials also stressed the need for older adults to receive a second booster shot or a fourth jab.

They noted that 89.5 percent of Covid-19 deaths over the past week occurred among people 60 and older.

Besides, the quarantine authorities pointed out that the period for reinfection has shortened from seven months to five months on average in July.

Also, those under 17 and unvaccinated people accounted for half of the total reinfections.

“To prevent reinfections, people have to abide by quarantine rules after initial infection and recovery and receive booster shots at recommended timing,” the KDCA said.