We aimed to identify the severity of the Coronavirus disease 2019 specifically according to the SARS-CoV-2 variant in the Republic of Korea by describing the number of severe/critical cases and deaths, case severity rate (CSR) and case fatality rate (CFR). A total of 23,496,849 confirmed cases were reported during January 20, 2020 to September 3, 2022. 26,472 (0.11%) cases were considered severe/critical and 27,471 (0.12%) resulted in death. The omicron BA.1/BA.2 period showed most severe/critical cases and deaths accounting for 40.7% (10,772 patients) and 66.4% (18,252 patients), respectively. In the omicron variant dominant period, the proportion of the age 80 and over saw on increase in severe/critical cases and deaths by 26.4%p, 7.4%p, respectively, than those in the delta dominant period. The CSR and CFR were 0.20% and 0.12% over that period. The CSR decreased from 2.98% in the pre-delta dominant period to 2.14% in the delta dominant period, and 0.14% in the omicron BA.1/BA.2 period. CFR was also highest at 1.15% in the pre-delta dominant period and decreased to 0.95% in the delta dominant period, 0.10% in the omicron BA.1/BA.2 period. Despite the increase in severity of the delta variant, overall severity decreased in the delta dominant period showing continuous decrease in the omicron dominant period. In the omicron dominant period, the proportion of the elderly of severe/critical and fatal condition increased which suggests the importance of focusing on the response strategy of the elderly.

Because of the COVID-19 pandemic, wastewater-based surveillance has garnered extensive attention in many countries, including the United States and those in Europe, by pre-emptively monitoring and responding to infectious diseases in the community. Additionally, it is actively used in national infectious disease monitoring policies. From 2021, the Korea Disease Control and Prevention Agency conducted a pilot project to prove the effectiveness of wastewater-based surveillance system in the Republic of Korea and laid the foundation to introduce a national wastewater-based surveillance system. In 2023, KOrea WAstewater Surveillance (KOWAS) project is being conducted in cooperation with 17 cities or provinces and 18 Institute of Health and Environment Researches. Henceforth, we will expand the scope of monitoring infectious diseases by cooperating with related ministries and prepare the crisis response for a potential pandemic by upgrading experimental techniques.