South Korea’s coronavirus disease situation is still uneasy although it is showing signs of calming down.

The number of daily new confirmed patients has bounced past 100 in five days -- on Wednesday it rose to 152. fell to 87 on Thursday, shot up to 147 on Friday and dipped to 98 on Saturday.

The rebound in the number of new confirmed cases is concerning, but more problematic is the persistent outbreak of cluster infections and steady influx of infected patients from abroad.

Cluster infections are the No. 1 cause for alarm, as they strike places vulnerable to mass contagions -- such as nursing homes, religious facilities and call centers. To make matters worse, it is almost impossible to grasp who started the contagion there. Particularly concerning is infections at nursing hospitals, which accommodate old and sick people, who are most vulnerable.

The Daegu City Metropolitan Government initiated coronavirus tests for all 33,610 workers and patients in more than 390 nursing hospitals and assisted living facilities on March 13. As of Saturday, the tests found about 190 cases, with nearly 150 of them concentrated in two nursing hospitals.

Considering that the tests are 87 percent completed and results have not come in yet for 3,949 people, some more additional COVID-19 cases are expected. A nursing hospital reportedly learned only after tests that the virus has sickened more than half of its patients -- thousands of nursing facilities are scattered across the country.

As the virus rages in Europe and the US, an influx of patients from abroad is steadily increasing. As of midnight Friday, 23 passengers from abroad were found to be infected during the airport entry procedure.

Some Koreans pushed ahead with overseas trips despite the pandemic and returned home after being infected. A family of three residing in Yongin, Gyeonggi Province, set out on March 9 to tour Britain, France, and the Netherlands and came back home on March 17, testing positive when they arrived.

Out of 15 Seoul citizens who tested positive on March 17-18, eight contracted the disease during their overseas trips. Penalty charges for tour cancellation might have been burdensome, but they should have taken into account the situation outside the country and refrained from traveling.

If the authorities fail to control overseas travel and entry into Korea effectively, the country can suffer a second round of COVID-19 outbreak similar to what hit Daegu and North Gyeongsang Province.

On March 19, the government extended a special entry procedure for arrivals from nine countries including Italy and Iran to all around the world. For instance, on March 17 alone, the procedure found suspected symptoms in 367 of 1,989 arrivals (19.3 percent). The ratio looks rather high, and will likely rise further, as the procedure expands and the government began to test all entrants from Europe for the virus on Sunday. The special entry procedure requires entrants to have their temperature taken at the airport and report self-check results daily for 14 days after entry.

A 17-year-old male student of a Daegu high school, without underlying diseases, died due to sudden pneumonia. The authorities said he posthumously tested negative for the virus, ending controversies over whether there were fallacies on the positive test results of his urine sample.

However, young people must not be relieved. A new study indicates that COVID-19 triggers in some people including young and healthy ones a cytokine storm, where one’s own immune system goes berserk, making the body’s response to the virus deadly. A 26-year-old patient with serious COVID-19 symptoms is known to be associated with cytokine storm.

In nutshell, there is no safe zone. If you give the virus a chance, it will give you a nasty bite.

Considering uncertainties about the swift development of vaccines or therapies, the pandemic is expected to last for some time. The overall spread in Korea has slowed down, but the situation is still volatile. A lax response may trigger a sudden surge. The authorities and public must not drop their guard.