New Covid-19 cases remained below 30 for more than a week on Thursday, pushing up the total to 10,613, the Korea Centers for Disease Control and Prevention said.

Hampering the public health authorities are spreads without symptoms and an increase in the number of people who are recovered but showed positive in retests, as well as continuous imported cases and possible cluster infections, especially after Wednesday’s parliamentary elections, officials said.

Korea reported 22 new Covid-19 cases as of midnight Wednesday. Hospitals discharged 141 more recovered people. Four more people died of the coronavirus, raising the death toll to 229.

Although Korea has been reporting new cases below 50 for two weeks, the nation continues to see clustered infections in some areas and foreign inflows. Over the past two weeks, 377 people, or 53.6 percent of the total newly confirmed people, were new arrivals. Cases have risen in part because self-isolators, including their families, have violated the quarantine measure.

Some uncertainties are also growing, caused by asymptomatic transmission and people testing positive after recovery, giving new headaches to public health officials.

Initially, the health authorities regarded re-diagnosed cases after full recovery as exceptions or special examples. As their number rises, however, the officials are keeping a close eye on the cause and possibility of them spreading the virus again.

Asymptomatic patients are equally dangerous, as they can spread the virus by continuing their daily lives without knowing they are infected. If these patients stay at nursing homes or medical institutions, there is a high chance of causing cluster infection in their facilities.

The health authorities said that there had been no cases of secondary infections from re-diagnosed patients. Still, they could not be entirely sure whether these patients do not infect others.

Experts believe that the virus that remained in the body after full recovery could have been re-activated when the patient’s immunity was weakened or a fragment of a dead virus gene without the ability of infection was found. Testing errors and genetic mutations of Covid-19 are also possible, they added.

Meanwhile, the government has formulated an additional budget of about 7.6 trillion won ($61.9 billion) to provide emergency relief funds to 14.48 million households at the bottom 70 percent of income level.

The Moon Jae-in administration, encouraged by a landslide victory at Wednesday’s general elections, will speed up this and other stimulus measures to sustain the virus-hit economy. A total of 11,515 self-isolated voters participated in the parliamentary polls.

“There seem to be some cases where the voters did not go out for election because they might have developed suspected symptoms,” an election official said. “The self-isolated voter turnout was similar to that of the general absentee ballot.”

As of midnight Wednesday, the nation tested 538,775 people and completed 524,507 tests. Among the tested people, 513,894 negatively responded to the test, and 14,268 people are waiting for results. The accumulated confirmation rate remained at 2 percent.