South Korea's daily new coronavirus cases remained in the 400s for the second consecutive day Monday partly due to fewer tests over the weekend, while health authorities are grappling with sporadic cluster infections across the nation.

The country reported 430 more COVID-19 cases, including 411 local infections, raising the total caseload to 140,340, the Korea Disease Control and Prevention Agency (KDCA) said.

The daily caseload was down from 480 on Sunday, when the figure fell below 500 for the first time in 20 days partly due to fewer tests over the weekend.

There were two additional deaths, raising the total to 1,959.

New cases popped up in various settings, including workplaces, churches and bars, and the number of untraceable cases remained high, posing challenges to the country's virus fight.

The proportion of untraceable cases stood at 28 percent over the past week, hovering over 20 percent since early December.

As the vaccine rollout among the elderly population gains pace, the government is set to ease social distancing guidelines for those who have received at least one shot of COVID-19 vaccines.

While up to eight immediate family members are currently allowed to gather, those who have received at least one shot of COVID-19 vaccines will be partly exempt from the social distancing rule starting Tuesday.

People who have gotten their first shots will be allowed to take their masks off outdoors starting in July.

The government aims to inoculate at least 13 million people, or a quarter of the country's population, by the end of June, as part of its goal to achieve herd immunity in November.

As the US government's supply of Johnson & Johnson's Janssen vaccine for 1 million people is set to arrive here this week, South Korea will be able to inoculate 14 million in the first half of this year, the KDCA said.

The Janssen vaccine from the US will be administered to reservists, civil defense members and diplomacy and defense-related officials who are aged 30 and over, on a preferential basis, in mid-June, it said.

A total of 5.4 million people, including 4,797 the previous day, have received their first shots of COVID-19 vaccines, taking up 10.5 percent of the total population, since the country started its vaccination program on Feb. 26.

AstraZeneca's vaccine has been given to 3.2 million people, while 2.1 million have received that of Pfizer.

The KDCA said 2.14 million people have been fully vaccinated, with an additional 87 receiving their second jabs the previous day, accounting for 4.2 percent of the total population.

Of the locally transmitted cases, 129 came from Seoul and 146 from the surrounding Gyeonggi Province.

The southeastern city of Daegu added 31 new patients, and the southeastern port city of Busan had 16 more cases.

There were 19 additional imported cases, down three from a day earlier.

The number of seriously or critically ill COVID-19 patients came to 149, down one from the previous day.

The total number of people released from quarantine after making full recoveries was 130,823, up 442 from a day earlier. (Yonhap)