As long as the COVID virus continues to mutate herd immunity to it will continue to be a fantasy despite such a high level of antibodies in the Korean population:

While a recent government study found that almost all Koreans have developed antibodies against the coronavirus either by vaccination or natural infection, this finding does not mean that the population has achieved herd immunity, according to health officials.
The Korea Disease Control and Prevention Agency (KDCA) unveiled on Friday the results of its latest study, which showed that 97.4 percent of those surveyed had antibodies against the spike protein (S) of the coronavirus. The survey, co-organized with the Korea National Institute of Health (NIH), involved some 10,000 people aged five and above living in 17 cities and provinces.
A COVID-19 antibody test checks whether an individual has developed S-antibodies or nucleocapsid protein (N)-antibodies. S-antibodies are produced either through natural infection or vaccination, while the N-antibodies are formed only through natural infection.
Although the vast majority of the population has developed antibodies against the coronavirus, people should still remain vigilant and receive an updated booster shot, health officials warn. (……)He also said that the latest study has only confirmed the presence of antibodies for the original COVID-19 virus, not for the Omicron variant and its subvariants.
Korea Times
“Antibodies diminish over time and the possible emergence of new variants may weaken the protection offered by antibodies from a previous variant,” he said, explaining that inoculation via a booster shot is essential after four months or longer following either infection or vaccination.
You can read more at the link, but calling for more booster shots is probably going to fall on deaf ears for most people at this point.