South Korea's daily new coronavirus cases stayed below 600 for the second straight day Monday on fewer tests over the weekend, with a rebound in the reproduction rate, coupled with sporadic cluster infections, straining the country's antivirus fight.

The country reported 538 more COVID-19 cases, including 513 local infections, raising the total caseload to 136,467, the Korea Disease Control and Prevention Agency (KDCA) said. The daily caseload stood at 585 on Sunday and 666 on Saturday.

There were three additional virus deaths, raising the total to 1,934. The fatality rate came to 1.42 percent.

Starting Monday, South Korea extended its tight social distancing scheme by three more weeks through June 13.

Currently, the greater Seoul area, home to more than half of the country's 52 million people, is under Level 2 social distancing, the third highest in the five-tier scheme, while the rest of the country is mostly subject to Level 1.5 distancing.

The guidelines limit operating hours of restaurants and bars to 10 p.m., with gatherings of five or more people banned nationwide. South Korea, however, has never imposed a full lockdown.

On Sunday, authorities said the country's reproduction rate reached 1.04, indicating that a COVID-19 patient transmits the virus to at least one person. It marked the first time for the figure to hover above one since mid-April.

South Korea has been grappling with sporadic cluster infections nationwide and more transmissible variant strains of COVID-19.

The country has reported more than 1,000 cases of COVID-19 variant strains from Britain, South Africa, Brazil and India.

Meanwhile, the country's inoculation scheme is expected to gather pace on increased shipments of vaccines.

Since late February, South Korea has completed the inoculation of 1.74 people, or 3.4 percent of the country's 52-million population.

A total of 3.79 million people, or 7.4 percent, have received their first shots. AstraZeneca's vaccine has been given to 2.06 million people, while 1.73 million have received that of Pfizer.

South Korea said the first batch of 55,000 doses of the Moderna vaccine will arrive here Saturday.

The country's drug watchdog approved the use of the Moderna product last week, and Samsung Biologics signed a deal to manufacture the vaccine here starting in August at the earliest.

The country has secured enough shots to fully vaccinate 99 million people, more than enough to vaccinate its entire population, including doses from the COVAX Facility project. Of the volume, Pfizer's vaccine accounts for 33 million, followed by Moderna's with 20 million.

The number of people with abnormal reactions after vaccination came to 24,366, up 236 from the previous tally. More than 95 percent of them, however, were minor symptoms such as headache and fever.

According to the health authorities, a total of 153 cases of deaths after inoculation have been reported so far, although authorities say they were not related with the vaccination.

Under the country's vaccination blueprint, the country aims to inoculate 13 million people by the end of June and achieve herd immunity by November.

Of the locally transmitted cases, 136 came from Seoul, and the surrounding Gyeonggi Province accounted for 120.

Imported cases came to 25, raising the total to 1,934.

Of the imported cases, India accounted for nine, followed by Indonesia with three cases.

The number of patients in serious or critical condition came to 144, down five from the previous day.

The total number of people released from quarantine after making full recoveries was 126,427, up 546 from a day earlier. Around 92.64 percent of the patients reported here were cured.

South Korea carried out 9,553,613 COVID-19 cases so far, including 17,314 from the previous day. (Yonhap)