Presumed population immunity to SARS-CoV-2 in South Korea, April 2022

Objectives: We estimated the overall and age- specific percentages of the Korean population with presumed immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as of April 2022 using the national registry. Methods: We used the national coronavirus disease 2019 (COVID-19) infection and vaccination registry from South Korea, as described to define individuals with a previous history of COVID-19 infection, vaccination, or both, as persons with presumed immunity. Results: Of a total of 53,304,627 observed persons, 24.4% had vaccination and infection, 58.1% had vaccination and no infection, 7.6% had infection and no vaccination, and 9.9% had no immunity. The SARS-CoV-2 Omicron variant emerged at a time when the presumed population immunity ranged from 80% to 85%; however, nearly half of the children were presumed to have no immunity. Conclusion: We report a gap in population immunity, with lower presumed protection in children than in adults. The approach presented in this work can provide valuable informed tools to assist vaccine policy-making at a national level.