Nursing home residents and staff under 65 years old are among the first in line for their second dose of the AstraZeneca vaccine starting Friday.
Those under 30, who received their first dose before the government's age restriction was implemented due to blood clot concerns, can decide themselves if they want it or not.
Around 926-thousand people are eligible for the second dose between now and June.
People who don't want the second dose now but choose to get it later will not be stripped of their priority recipient status.
However, health authorities are urging active participation, noting that data from abroad shows side effects are less frequent for the second dose.
The roll out is expected to kickstart the recent slowdown in South Korea's vaccine campaign along with the nationwide distribution of millions of AstraZeneca vaccines from Friday to early June.
"Our supply is enough to vaccinate 13 million people with their first doses by late June. Now is the time to focus on actually inoculating people with the vaccines we've procured."
So far, only some 825-thousand people, or one.six percent of South Korea's population, have been fully vaccinated.
And with 7,139 more recipients, the number of people who've received their first dose remains at around three.seven million or about 7.2 percent of the population.
Meanwhile, South Korea reported 747 new cases of COVID-19 on Friday with cluster infections still popping up nationwide.
It's the second day in a row for the daily figure to be in the seven hundred range, pushing the total number of cases over 130-thousand.
All but 18 of Friday's new cases were transmitted locally, with regions outside the capital area accounting for over 40 percent of the total.
Two more people died, raising the national COVID-19 death toll to one,893.
Han Seong-woo, Arirang News.