This report seeks to compare and analyze the severity trends of coronavirus disease 2019 (COVID-19) in Republic of Korea during periods of dominant variant virus prevalence. The analysis covers the period from January 20, 2020, to July 31, 2023, categorizing the severity of COVID-19 cases both throughout the entire period and during periods of dominant variant virus prevalence. Up until July 31, 2023, a total of 34,082,179 confirmed cases of COVID-19 have been recorded, resulting in 37,760 cases (0.11%) of severe illness and 35,644 deaths (0.11%). During the dominant prevalence of the Omicron BA.1 and BA.2 variants (from January 16, 2022 to July 9, 2022), severe cases and deaths were most widespread, accounting for 10,460 cases (27.7%) of severe illness and 18,679 deaths (52.4%). Concerning case severity rate and case fatality rate, the period before the dominant prevalence of the Delta variant (from January 20, 2020 to July 24, 2021) had the highest rates at 2.98% and 1.15%, respectively. In contrast, during the dominant prevalence of the Omicron XBB variant (from April 16, 2023 to July 31, 2023), these rates were at their lowest, reaching 0.12% for severity and 0.04% for fatality. Despite the continuous emergence of new variant viruses after the onset of COVID-19, the case severity rate during the dominant prevalence of the Omicron XBB variant has decreased to 0.04%, comparable to the risk level seen with influenza. However, the case fatality rate by age group is <0.01% for 0-49 years old, 0.01% for 50-59 years old, and 0.03% for 60-69 years old, while the case fatality rate for 80+ years old is 0.56%, which is still higher than other age groups, so the prevention policy of prioritizing high-risk groups should be continued.