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Public Health Weekly Report 2023; 16(43): 1464-1487

Published online September 26, 2023

https://doi.org/10.56786/PHWR.2023.16.43.2

© The Korea Disease Control and Prevention Agency

Severity of COVID-19 Associated with SARS-CoV-2 Variants Dominant Period in the Republic of Korea

Se-Jin Jeong1, Misuk An1, Minjeong Jang1, So Young Choi1,2, You-Jung Choi1, Jinhwa Jang1,2, Boyeong Ryu1,2, Shin Young Park1,2, Seong-Sun Kim1,2*

1Data Analysis Team, Epidemiological Investigation and Analysis Task Force, Central Disease Control Headquarters, Korea Disease Control and Prevention Agency (KDCA), Cheongju, Korea,
2Division of Public Health Emergency Response Research, Korea Disease Control and Prevention Agency (KDCA), Cheongju, Korea

*Corresponding author: Seong-Sun Kim, Tel: +82-43-719-7730, E-mail: sskim0719@korea.kr

Received: September 1, 2023; Revised: September 13, 2023; Accepted: September 25, 2023

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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.

Key words COVID-19; SARS-CoV-2; COVID-19 severity; COVID-19 variants; COVID-19 deaths

Key messages

① What is known previously?

The severity of COVID-19 in Republic of Korea decreased during the Delta dominance period, despite the increase in delta variant-specific severity, and continued to decrease during the omicron dominance period.

② What new information is presented?

Peak case severity and case fatality rate were in the Pre- Delta dominance period (2020.1.20.–2022.7.24., 2.98% and 1.15%), lowest during Omicron XBB dominance period (2023.4.16.–2023.7.31., 0.12% and 0.04%).

③ What are implications?

As new COVID-19 variants emerge, Omicron XBB had a 0.04% case severity rate, lower than seasonal influenza. However, case fatality rate in the 80+ group remain high, underlining the importance of prioritizing high-risk individuals.

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While most people infected with this virus experience mild to moderate respiratory diseases and can recover without special treatment, certain groups such as older adults and those with underlying conditions such as cardiovascular disease, diabetes, or chronic respiratory disease require medical attention [1]. As of August 2, 2023, the World Health Organization (WHO) reported a global total of 768,983,095 confirmed cases with 11,740,993 deaths and a case fatality rate of 1.0%. A total of 13,492,099,754 vaccine doses were administered worldwide. In the Republic of Korea (ROK), during the same period, there were 33,322,073 confirmed cases and 35,339 deaths, with a case fatality rate of 0.11%. In comparison, seasonal influenza, a respiratory infection similar to COVID-19, had an incidence rate of 16.9 per 1,000 outpatients as of July 25, 2023 [2], with a case fatality rate of 0.03–0.07% globally and 0.03–0.08% in the ROK according to the WHO [3]. Furthermore, in terms of the primary vaccination, 44,327,956 individuals have received vaccination, indicating a vaccination rate of 86.7% relative to the national population [4].

SARS-CoV-2 undergoes mutations as it spreads across various countries and infects new hosts over time [5]. While these mutations may not significantly alter the properties of the virus, they can impact public health and societal aspects such as transmission, disease severity, vaccine effectiveness, and therapeutics [6].

The WHO classified variant viruses into variants of interest (VOI) and variants of concern (VOC) to prioritize research and monitoring of these strains. Accordingly, the WHO is implementing ‘SARS-CoV-2 variant tracking monitoring,’ and the U.S. Centers for Disease Control and Prevention is implementing the ‘National SARS-CoV-2 Genomic Surveillance System,’ ‘National Wastewater Surveillance System,’ and ‘Traveler-based SARS-CoV-2 Genomic Surveillance program’ [6,7]. ROK also actively is monitoring them according to the variant virus classification system [8]. The VOC were designated and managed in the following order: the Alpha and Beta variants in December 2020, the Gamma variant in January 2021, the Delta variant in May 2021, and the Omicron variant in November 2021 [9]. Over time, the COVID-19 virus has shown increasing diversity, with dominant strains having lower severity and reduced infection risk due to vaccination [10-12]. Notably, the Omicron variant exhibits higher transmissibility and reduced hospitalization periods by 15–20%, with a 41% (95% confidence interval: 37–45%) decrease in the risk of hospitalization lasting one or more nights, depending on vaccination status [13]. As of August 2023, the number of confirmed COVID-19 cases and deaths has decreased worldwide, with no emergence of new highly pathogenic or contagious new variants reported [14].

Therefore, this study aims to assess the occurrence and current status of patients with severe or critical conditions and deaths in the ROK during the dominance of SARS-CoV-2 variants. By comparing the rates of case severity and case fatality, this research intends to contribute fundamental data to prioritize and define the scope for future COVID-19 management adjustments, particularly in terms of infectious disease classification. The findings will serve as fundamental data for planning healthcare resource allocation.

1. Study Population

We included individuals with confirmed COVID-19 reported to the COVID-19 Information Management System of the Korea Disease Control and Prevention Agency (KDCA) from January 20, 2020 to July 31, 2023; the scale of the occurrence and demographic characteristics of those whose condition progressed to critical condition or those who died were analyzed separately during the entire period following the dominance periods of COVID-19 virus variants. A patient with confirmed COVID-19 was defined as a person whose disease status was determined by genetic tests of the virus or whose infection was confirmed by isolating the virus regardless of clinical symptoms or a person who showed symptoms of COVID-19 whereby the infection was confirmed with a rapid antigen (for professional use/implemented on March 14, 2022) or emergency screening tests. Severe COVID-19 cases were classified as those who, after COVID-19 confirmation, received non-invasive ventilation, high-flow oxygen therapy, invasive ventilation, multi-organ failure, extracorporeal membrane oxygenation, or continuous renal replacement therapy while quarantined in a medical institution [15]. The clinical condition of confirmed patients was monitored based on data and telephone communication reported to the ‘COVID-19 Information Management System’ (KDCA) and the ‘Health and Medical Resources Integrated Reporting Portal System’ (Central Disaster Management Headquarters). Information on COVID-19 deaths was collected from individuals reported through the Integrated Disease and Health Management System of the KDCA according to the “Infectious Disease Control and Prevention Act.” The study focused on COVID-19-related deaths, excluding cases of foreign nationals.

2. Data Analysis

To understand the scale and characteristics of the occurrence of severe and critical patients and deaths, demographic characteristics, including sex and age, incidence status by reported area according to the epidemic periods, were calculated based on the date of diagnosis confirmation. In addition, the severity of COVID-19 was categorized into two stages to assess the impact of viral mutations on disease severity, and we calculated the case severity rate and case fatality rates for both the entire epidemic period and by weeks.

The dominance period was classified based on the week in which more than 50% of the weekly variant virus tests detected the VOI, according to the SARS-CoV-2 variant analysis report date. Of the entire period, the dominance period was divided into the Delta variant (reported from July 25, 2021–January 15, 2022), the Omicron BA.1 and BA.2 variant (January 16, 2022–July 9, 2022), the Omicron BA.5 variant (July 24, 2022–December 31, 2022), the Omicron BN.1 variant (January 22, 2023–March 25, 2023), and the Omicron XBB variant (April 16, 2023–July 31, 2023) dominance periods, and cases reported at times not included in the dominance periods were excluded from the analysis. In addition, since no sublineages of the Omicron XBB with an occupancy rate of 30% or higher have been confirmed to date [16], we analyzed the Omicron XBB variant period as a whole. The case severity rate was calculated as the proportion (%) of patients with severe or critical conditions and deaths among confirmed cases reported in the relevant period (dominance period of the virus’ variants), and the case fatality rate was calculated as the proportion (%) of deaths among confirmed cases occurring in the relevant period (the virus’ variant dominance period). In addition, to calculate the scale of deaths per 100,000 population relative to the total population (mortality rate), resident registration central population data (population distribution representing the relevant year) registered with Statistics Korea were used [17], and the case severity rate, case fatality, and mortality rates were stratified by dividing age groups into 10-year increments to compare severity by age. We used the Microsoft Excel 2018 (Microsoft) and Tableau ver. 2021.4 (Salesforce) for all of the analysis.

Since the COVID-19 outbreak, a total of 34,082,179 confirmed cases had been reported until July 31, 2023. Compared to the total number of confirmed cases of 34,082,179, the period before the dominant prevalence of the Delta variant had 0.5% (187,340 cases) of confirmed cases, the Delta variant had 1.5% (500,414 cases), and the Omicron variants had 52.2% (17,800,369 cases) for BA.1 and BA.2, 29.1% (9,912,503 cases) for BA.5, 2.3% (777,942 cases) for BN.1, and 6.5% (2,224,486 cases) for XBB. Among all confirmed cases, the condition in a total of 63,522 cases (0.19%) progressed to severe conditions or death during the entire study period. Of these, 37,760 cases (0.11%) were classified as patients with severe or critical conditions, and 35,644 cases (0.11%) deceased. Among patients whose condition progressed to severe conditions after a COVID-19 diagnosis, 9,882 cases (0.03%) eventually died.

1. Status of Patients with Severe or Critical Conditions

A total of 37,760 patients with severe or critical conditions were identified during the COVID-19 outbreak. The period in which the most patients with severe or critical conditions occurred by variant dominance period was when the Omicron variants BA.1 and BA.2 were dominant, accounting for the highest occurrence of patients with severe or critical conditions at 27.7% (10,460 cases) (Table 1). Following that, during the Omicron BA.5 dominance period, 23.0% (8,675 cases) patients with severe or critical conditions were reported. Comparing the Omicron BA.1 and BA.2 dominance period to the Delta variant dominance period, a significant increase (35.6-fold) was noted in the number of confirmed cases, which also led to a 1.3-fold increase in patients with severe or critical conditions. However, due to the reduced severity associated with Omicron, the increase in patients with severe or critical conditions during this period remained at a lower level (Figure 1). Regarding sex distribution, the proportion of men in the entire period was 57.7%, which was 15.4%p higher than that of women. The average age of patients in patients with severe or critical conditions was 72.3 years (standard deviation [SD]±15.7 years), showing a gradual increase in average age from the Pre-Delta variant dominance period at 67.7 years (SD±13.7 years) and the Delta variant dominance period at 66.1 years (SD±15.4 years) to the Omicron BA.1/2 dominance period at 72.7 years (SD±15.7 years) and the Omicron BA.5 dominance period at 75.0 years (SD±15.4 years). In terms of age groups, those aged 60 years and above accounted for the highest proportion, with 30,866 cases (81.7%). Among this age group, during the Omicron BA.5 dominance period, the proportion reached 88.1%, the highest of all periods. Following that, during the Omicron XBB dominance period, it was 87.1%. Notably, the age group of 80 years and above, which accounted for 19.6% during the Delta variant dominance period, increased by approximately 2.1-fold to an average of 42.3% during the Omicron period. Regarding area distribution, the metropolitan area (Seoul, Gyeonggi, Incheon) accounted for more than half, at 61.9% (23,347 cases), throughout the entire period, while non-metropolitan area contributed 37.8% (14,287 cases). Based on reporting areas, Seoul reported the highest number of cases at 10,337 (27.4%), followed by Gyeonggi with 10,183 cases (27.0%). When analyzed by dominant variant periods, the metropolitan area reported the highest proportions in both the Pre-Delta variant dominance period (72.9%) and the Delta variant dominance period (74.5%). In addition, during the Omicron XBB dominance period, non-metropolitan areas accounted for over half (54.0%) of the cases. However, during other variant periods, the majority of cases were reported in the metropolitan area (Delta: 74.5%; BA.1, BA.2: 57.1%; BA.5: 57.2%; BN.1: 52.2%). In particular, among the 126 cases reported in quarantine, the Pre-Delta variant dominance period had the highest count at 97 cases (2.1%), followed by the Delta variant dominance period with 27 cases (0.3%).

Figure 1. Weekly number of confirmed cases, severe/critical cases and deaths (as of July 31, 2023)

Table 1. Characteristics of COVID-19b) severe/critical casesa) by period (as of as of July 31, 2023)
ClassVariants dominant period
Total (2020.1.20.-2023.7.31.)Pre-Delta (2020.1.20.-2021.7.24.)Delta dominant period (2021.7.25.-2022.1.15.)Omicron dominant period
BA.1/BA.2 (2022.1.16.-2022.7.9.)BA.5 (2022.7.24.-2022.12.31.)BN.1 (2023.1.22.-2023.3.25.)XBB (2023.4.16.-2023.7.31.)
Total37,760 (100.0)4,665 (100.0)8,296 (100.0)10,460 (100.0)8,675 (100.0)1,364 (100.0)2,028 (100.0)
Sex
Male21,787 (57.7)2,792 (59.8)4,775 (57.6)6,029 (57.6)4,886 (56.3)811 (59.5)1,199 (59.1)
Female15,973 (42.3)1,873 (40.2)3,521 (42.4)4,431 (42.4)3,789 (43.7)553 (40.5)829 (40.9)
Age (yr)
Average±standard deviation72.3±15.767.7±13.766.1±15.472.7±15.775.0±15.473.6±15.673.6±15.5
0-9209 (0.6)0 (0.0)6 (0.1)74 (0.7)67 (0.8)12 (0.9)25 (1.2)
10-19158 (0.4)3 (0.1)21 (0.2)65 (0.6)47 (0.5)7 (0.5)5 (0.3)
20-29385 (1.0)44 (0.9)129 (1.6)108 (1.0)63 (0.7)13 (1.0)11 (0.5)
30-39899 (2.4)116 (2.5)399 (4.8)193 (1.9)112 (1.3)20 (1.5)28 (1.4)
40-491,694 (4.5)298 (6.4)664 (8.0)343 (3.3)241 (2.8)39 (2.8)51 (2.5)
50-593,549 (9.4)730 (15.6)1,150 (13.9)777 (7.4)506 (5.8)93 (6.8)141 (7.0)
60-697,821 (20.7)1,240 (26.6)2,218 (26.7)2,045 (19.6)1,315 (15.2)225 (16.5)379 (18.7)
70-799,968 (26.4)1,289 (27.6)2,084 (25.1)2,805 (26.8)2,242 (25.8)396 (29.0)532 (26.2)
≥8013,077 (34.6)945 (20.3)1,625 (19.6)4,050 (38.7)4,082 (47.1)559 (41.0)856 (42.2)
≥6030,866 (81.7)3,474 (74.5)5,927 (71.4)8,900 (85.1)7,639 (88.1)1,180 (86.5)1,767 (87.1)
Region
Metropolitan area23,347 (61.9)3,402 (72.9)6,184 (74.5)5,975 (57.1)4,960 (57.2)713 (52.2)932 (46.0)
Seoul10,337 (27.4)1,876 (40.2)3,348 (40.3)2,275 (21.7)1,707 (19.7)276 (20.2)412 (20.3)
Gyeonggi10,183 (27.0)1,238 (26.5)2,255 (27.2)2,746 (26.3)2,589 (29.8)359 (26.3)420 (20.7)
Incheon2,827 (7.5)288 (6.2)581 (7.0)954 (9.1)664 (7.7)78 (5.7)100 (5.0)
Non-metropolitan area14,287 (37.8)1,166 (25.0)2,085 (25.2)4,484 (42.9)3,714 (42.8)651 (47.8)1,096 (54.0)
Busan2,347 (6.2)156 (3.3)433 (5.2)723 (6.9)566 (6.5)108 (7.9)189 (9.3)
Deagu1,806 (4.8)240 (5.1)258 (3.1)613 (5.9)412 (4.7)54 (4.0)130 (6.4)
Gwangju811 (2.2)65 (1.4)70 (0.9)301 (2.9)229 (2.6)29 (2.1)47 (2.3)
Daejeon883 (2.3)71 (1.5)168 (2.0)269 (2.6)209 (2.4)36 (2.6)61 (3.0)
Ulsan660 (1.8)75 (1.6)99 (1.2)196 (1.9)177 (2.0)23 (1.7)43 (2.1)
Sejong82 (0.2)2 (0.0)12 (0.2)31 (0.3)23 (0.3)3 (0.2)4 (0.2)
Gangwon1,338 (3.5)99 (2.1)175 (2.1)444 (4.2)361 (4.2)65 (4.8)95 (4.7)
Chungbuk754 (2.0)64 (1.4)138 (1.7)265 (2.5)172 (2.0)32 (2.4)41 (2.0)
Chungnam1,486 (3.9)97 (2.1)226 (2.7)395 (3.8)470 (5.4)61 (4.5)115 (5.7)
Jeonbuk711 (1.9)58 (1.2)81 (1.0)247 (2.4)183 (2.1)33 (2.4)54 (2.7)
Jeonnam758 (2.0)42 (0.9)63 (0.8)239 (2.3)205 (2.4)43 (3.2)88 (4.3)
Gyeongbuk1,020 (2.7)94 (2.0)100 (1.2)274 (2.6)311 (3.6)69 (5.1)77 (3.8)
Gyeongnam1,403 (3.7)88 (1.9)235 (2.8)404 (3.9)370 (4.3)81 (5.9)109 (5.4)
Jeju228 (0.6)15 (0.3)27 (0.3)83 (0.8)26 (0.3)14 (1.0)43 (2.1)
Quarantine126 (0.3)97 (2.1)27 (0.3)1 (0.0)1 (0.0)0 (0.0)0 (0.0)

Unit: n (%). a)Severe/critical case: Patient who were treated with non-invasive ventilation, high flow oxygenation, invasive ventilation, extracorporeal membrane oxygenation, continuous renal replacement treatment during quarantine from coronavirus disease 2019. b)Number of confirmed cases (≥80): Pre-Delta dominant period 187,340 (6,083, 3.2%), Delta dominant period 500,414 (15,600, 3.1%), Omicron BA.1/BA.2 dominant period 17,800,369 (516,128, 2.9%), Omicron BA.5 dominant period 9,912,503 (411,067, 4.1%), Omicron BN.1 dominant period 777,942 (42,126, 5.4%), Omicron XBB dominant period 2,224,486 (112,926, 5.1%).



2. Deaths

Among the total 35,644 deaths reported during the entire COVID-19 pandemic period, the majority, 52.4% (18,679 cases), occurred during the Omicron BA.1 and BA.2 dominance period (Table 2). During the Omicron BA.1 and BA.2 dominance period, there was a simultaneous increase in confirmed cases (35.6-fold) and deaths (3.9-fold). However, in terms of severity, compared to the increase in confirmed cases during the Omicron dominance period, the rise in deaths remained at a lower level (Figure 1). Regarding sex distribution of patients, 50.6% (18,029 cases) were women and 49.4% (17,615 cases) were men. However, except for the Omicron BA.1 and BA.2 dominance period, in other variant periods, males had a higher mortality rate than females, as indicated by a majority of deaths. The overall average age was 79.2 years (SD±12.2 years), that for the period of the dominant prevalence of the Pre-Delta variant was 78.4 years (SD±11.4 years), the Delta variant dominance period was 77.2 years (SD±12.2 years), the Omicron BA.1 and BA.2 dominance period was 80.4 years (SD±12.1 years), the Omicron BA.5 dominance period was 80.2 years (SD±12.2 years), BN.1 dominance period was 78.8 years (SD±12.7 years), and XBB was 80.4 years (SD±11.9 years), which meant deaths were found to generally be within the age range of 70s to 80s. Exploring the different age groups, excluding 48.0% (2,292 cases) of the people of the Delta variant dominance period, the proportion of people aged 80 or older was more than half in the period before the dominant prevalence of the Pre-Delta variant (52.4%) and all the Omicron variants dominance periods (58.2% to 63.8%), and people over 60 age group accounted for more than 90% of the total age (92.4% to 95.3%). Regarding area distribution, more than half of the deaths occurred in non-metropolitan areas at 51.7% (18,443 cases) during the entire period, whereas those in the metropolitan area accounted for 48.2% (17,185 cases). Based on reporting areas, Gyeonggi had the highest number of deaths, with 8,586 (24.1%), followed by Seoul with 6,638 (18.6%). When divided by period for each variant, more than half of the deaths occurred in the metropolitan area in the pre-Delta and the Delta dominance periods, at 61.8% and 74.3%, respectively, and in other variant periods, more than half of the deaths occurred in non-metropolitan areas (BA.1, BA.2: 56.9%; BA.5: 56.6%; BN.1: 63.0%; XBB: 59.0%).

Table 2. Characteristics of coronavirus disease 2019 deaths by period (as of July 31, 2023)
ClassVariants dominant period
Total (2020.1.20.-2023.7.31.)Pre-Delta (2020.1.20.-2021.7.24.)Delta dominant period (2021.7.25.-2022.1.15.)Omicron dominant period
BA.1/BA.2 (2022.1.16.-2022.7.9.)BA.5 (2022.7.24.-2022.12.31.)BN.1 (2023.1.22.-2023.3.25.)XBB (2023.4.16.-2023.7.31.)
Total35,644 (100.0)2,163 (100.0)4,772 (100.0)18,679 (100.0)6,838 (100.0)809 (100.0)984 (100.0)
Sex
Male17,615 (49.4)1,091 (50.4)2,487 (52.1)8,881 (47.5)3,455 (50.5)444 (54.9)527 (53.6)
Female18,029 (50.6)1,072 (49.6)2,285 (47.9)9,798 (52.5)3,383 (49.5)365 (45.1)457 (46.4)
Age (yr)
Average±standard deviation79.2±12.278.4±11.477.2±12.280.4±12.180.2±12.278.8±12.780.4±11.9
0-939 (0.1)0 (0.0)3 (0.1)21 (0.1)10 (0.1)0 (0.0)2 (0.2)
10-1924 (0.1)0 (0.0)0 (0.0)13 (0.1)6 (0.1)3 (0.4)1 (0.1)
20-2981 (0.2)5 (0.2)10 (0.2)48 (0.3)15 (0.2)0 (0.0)1 (0.1)
30-39166 (0.5)11 (0.5)33 (0.7)70 (0.4)33 (0.5)8 (1.0)5 (0.5)
40-49480 (1.3)20 (0.9)79 (1.7)242 (1.3)94 (1.4)12 (1.5)10 (1.0)
50-591,446 (4.1)105 (4.9)233 (4.9)708 (3.8)269 (3.9)38 (4.7)28 (2.8)
60-694,044 (11.3)284 (13.1)822 (17.2)1,897 (10.1)684 (10.0)99 (12.2)103 (10.6)
70-798,065 (22.6)604 (28.0)1,300 (27.2)4,001 (21.4)1,476 (21.6)178 (22.0)206 (20.9)
≥8021,299 (59.8)1,134 (52.4)2,292 (48.0)11,679 (62.5)4,251 (62.2)471 (58.2)628 (63.8)
≥6033,408 (93.7)2,022 (93.5)4,414 (92.4)17,577 (94.0)6,411 (93.8)748 (92.4)937 (95.3)
Region
Metropolitan area17,185 (48.2)1,337 (61.8)3,544 (74.3)8,048 (43.1)2,971 (43.4)299 (37.0)403 (41.0)
Seoul6,638 (18.6)555 (25.7)1,717 (36.0)2,719 (14.6)1,105 (16.1)117 (14.5)193 (19.6)
Gyeonggi8,586 (24.1)714 (33.0)1,541 (32.3)4,244 (22.7)1,526 (22.3)131 (16.2)158 (16.1)
Incheon1,961 (5.5)68 (3.1)286 (6.0)1,085 (5.8)340 (5.0)51 (6.3)52 (5.3)
Non-metropolitan area18,443 (51.7)814 (37.6)1,224 (25.6)10,631 (56.9)3,867 (56.6)510 (63.0)581 (59.0)
Busan2,926 (8.2)130 (6.0)245 (5.1)1,878 (10.1)441 (6.4)44 (5.4)80 (8.1)
Deagu2,061 (5.8)222 (10.3)166 (3.5)1,026 (5.5)453 (6.6)56 (6.9)51 (5.2)
Gwangju858 (2.4)24 (1.1)48 (1.0)536 (2.9)172 (2.5)19 (2.3)19 (1.9)
Daejeon991 (2.8)34 (1.6)157 (3.3)529 (2.8)169 (2.5)32 (4.0)29 (2.9)
Ulsan544 (1.5)40 (1.8)28 (0.6)314 (1.7)116 (1.7)11 (1.4)13 (1.3)
Sejong59 (0.2)1 (0.0)3 (0.1)32 (0.2)12 (0.2)1 (0.1)3 (0.3)
Gangwon1,388 (3.9)56 (2.6)65 (1.4)769 (4.1)346 (5.1)36 (4.5)54 (5.5)
Chungbuk1,087 (3.0)71 (3.3)55 (1.2)629 (3.4)218 (3.2)28 (3.5)34 (3.5)
Chungnam1,635 (4.6)46 (2.1)139 (2.9)896 (4.8)413 (6.0)38 (4.7)40 (4.1)
Jeonbuk1,270 (3.6)60 (2.8)65 (1.4)802 (4.3)223 (3.3)35 (4.3)28 (2.8)
Jeonnam1,071 (3.0)18 (0.8)30 (0.6)548 (2.9)309 (4.5)53 (6.5)61 (6.2)
Gyeongbuk2,161 (6.1)88 (4.1)114 (2.4)1,301 (7.0)463 (6.8)52 (6.4)51 (5.2)
Gyeongnam2,077 (5.8)23 (1.1)97 (2.0)1,196 (6.4)476 (7.0)97 (12.0)85 (8.6)
Jeju315 (0.9)1 (0.0)12 (0.3)175 (0.9)56 (0.8)8 (1.0)33 (3.4)
Quarantine16 (0.0)12 (0.6)4 (0.1)0 (0.0)0 (0.0)0 (0.0)0 (0.0)

Unit: n (%).



3. Trends in Case Severity and Fatality Rates

During the entire pandemic, the case severity rate was 0.19%, and the case fatality rate was 0.10%. In terms of different epidemic periods, the case severity rate and case fatality rates were the highest at 2.98% and 1.15%, respectively, in the pre-Delta dominance period, followed by the case severity rate and case fatality rates at 2.14% and 0.95%, respectively, in the Delta dominance period. The case severity rate and case fatality rates were the lowest at 0.12% and 0.04%, respectively, in the Omicron XBB dominance period (Table 3, Figure 2). The case severity rate decreased from 2.98% in the pre-Delta dominance period to 0.14% in the Omicron BA.5 dominance period. However, it increased in the Omicron BN.1 dominance period (0.25%) and then showed a trend of decreasing again to 0.12% in the Omicron XBB dominance period. The case fatality rate was also the highest in the pre-Delta variant dominance period at 1.15% and showed a decreasing trend until the Omicron BA.5 dominance period (0.07%). However, there was an increase (0.10%) during the Omicron BN.1 dominance period, followed by another decline (0.04%) during the Omicron XBB dominance period. Compared to the Delta variant dominance period, the Omicron XBB dominance period experienced a significant reduction in case fatality rates, amounting to a 29-fold decrease.

Figure 2. Weekly case severity rate and case fatality rate (as of July 31, 2023)

Table 3. Case severity rate and case fatality rate by variant dominant period (as of July 31, 2023)
ClassVariants dominant period
Total (2020.1.20.-2023.7.31.)Pre-Delta (2020.1.20.-2021.7.24.)Delta dominant period (2021.7.25.-2022.1.15.)Omicron dominant period
BA.1/BA.2 (2022.1.16.-2022.7.9.)BA.5 (2022.7.24.-2022.12.31.)BN.1 (2023.1.22.-2023.3.25.)XBB (2023.4.16.-2023.7.31.)
Case severity rate (yr)a)0.192.982.140.150.140.250.12
0-90.010.000.02<0.010.010.030.03
10-19<0.010.020.04<0.01<0.010.01<0.01
20-290.010.150.190.010.010.01<0.01
30-390.020.450.560.010.010.020.01
40-490.041.040.980.020.020.040.02
50-590.102.261.910.060.050.110.05
60-690.275.313.590.190.140.300.15
70-790.7513.638.880.700.470.870.34
≥802.4225.4219.752.731.742.131.18
Case fatality rate (yr)b)0.101.150.950.100.070.100.04
0-9<0.010.000.01<0.01<0.010.00<0.01
10-19<0.010.000.00<0.01<0.01<0.01<0.01
20-29<0.010.020.01<0.01<0.010.00<0.01
30-39<0.010.040.04<0.01<0.010.01<0.01
40-490.010.070.110.010.010.01<0.01
50-590.030.310.360.030.020.040.01
60-690.111.141.170.110.060.100.03
70-790.405.594.420.470.220.300.11
≥801.7418.6414.692.261.031.120.56
Mortality rate (per 1,000,000) (yr)69.294.209.2836.3113.291.571.91
0-91.100.000.080.590.280.000.06
10-190.510.000.000.280.130.060.02
20-291.260.080.160.750.230.000.02
30-392.510.170.501.060.500.120.08
40-495.950.250.983.001.160.150.12
50-5916.791.222.718.223.120.440.33
60-6954.623.8411.1025.629.241.341.39
70-79210.8115.7933.98104.5838.584.655.38
≥80944.0750.26101.59517.67188.4220.8827.84

Unit: %. a)Case severity rate: (number of severe/critical cases and deaths among confirmed cases in specific period)/number of confirmed cases in specific period×100. b)Case fatality rate: (number of deaths among confirmed cases in specific period)/number of confirmed cases in specific period×100.



The case severity rate, case fatality, and mortality rates according to age in each period all increased with advancing age. Across different age groups, as the epidemic transitioned from the Delta variant dominance period to the Omicron BA.1/2 dominance period, a decreasing trend in case severity rate and case fatality rates was observed for all age groups. The age group with the most substantial relative reduction in case severity rate during this transition was the 30s (from 0.56% to 0.01%, a 60.3-fold decrease), followed by the 40s (from 0.98% to 0.02%, a 32.9-fold decrease). The age group with the least relative decrease was the 80s (from 19.75% to 2.73%, a 7.2-fold decrease). A similar pattern was observed in the age-specific case fatality rates, with the 30s (0.04% to <0.01%, a 16.8-fold decrease) experiencing the most substantial relative decrease and the 80s (14.69% to 2.26%, a 6.5-fold decrease) having the least relative decrease. During the Omicron BA.5 and BN.1 dominance periods, all age groups except the over 80s had case severity and case fatality rates below 1%. During the Omicron XBB dominance period, except for a case severity rate of 1.18% in the over 80 age group, all other age groups had exhibited case severity rate and case fatality rates below 1%.

The mortality rate reached its highest at 36.31 deaths per 100,000 people during the Omicron BA.1/2 dominance period, characterized by a sharp increase in confirmed cases nationwide, followed by the Omicron BA.5 dominance period with a rate of 13.29 deaths per 100,000 people. For the over 80 age group, the mortality rate was 944.07 deaths per 100,000 people. In addition, when classified by the dominance period, the mortality rate was maintained at more than 100 per 100,000 population in the Delta variant, Omicron BA.1/2, and Omicron BA.5 dominance periods, while the Pre-Delta variant dominance period had a rate of 50.26, the Omicron BN.1 dominance period had a rate of 20.88, and the Omicron XBB dominance period had a rate of 27.84, all showing a declining trend.

Following a previous report [18] that analyzed the case severity rate trend from the date of the first confirmed case of COVID-19 in the ROK to the Omicron BA.5 dominance period, this report compared and analyzed the severity trends until the Omicron XBB dominance period. The average incubation period of the Omicron variant is 4.2 days (range: 2–8 days), which is shorter than that of the Delta variant at 5.8 days. The Omicron variant is reported to have a higher transmissibility of infection than other variants such as the Delta variant due to increased antibody evasion [19]. In addition, when exploring each epidemic period, the case severity rate and case fatality rates in the Delta variant dominance period were 2.14% and 0.95%, respectively, and the case severity rate and case fatality rates in the Omicron XBB dominance period were 0.12%, and 0.04%, respectively, showing that the number of infected cases increased rapidly through the Omicron variant, but with decreasing severity levels. This aligns with prior research, which has indicated that the Omicron variant is associated with milder symptoms and reduced severity in comparison to other variants [20,21]. Reflecting this decreasing trend of lower case severity rate and case fatality rates, the Central Disaster Management Headquarters lowered the COVID-19 crisis level from ‘severe’ to ‘alert’ as from June 1, 2023 [22]. However, it is important to note that the number of confirmed cases has continued to increase since the Omicron XBB dominance period from March 2023 to July 2023. This can be attributed to the highly transmissible nature of the Omicron XBB variant and the effects of the crisis-level adjustment. Nevertheless, case severity rate, case fatality rates, and mortality rates have been gradually decreasing during these periods. However, there are age-specific variations in case severity rate and case fatality rates, with the over 80 age group being the least affected. The most significant disparities were observed in the 20s and 30s age groups. This aligns with the trend of decreasing disparities with increasing age (Table 3), potentially related to the impact of age on the immune system [23] and research indicating reduced vaccine efficacy among those over 65 age group [24]. Additionally, the case fatality rate (0.04%) during the ongoing Omicron XBB dominance period is at the level of the case fatality rate of seasonal influenza (0.03% to 0.08%), which is lower than that of other variant dominance periods [3]. This indicates a diminished disease risk and implies the potential for a gradual relaxation of epidemic control measures. Nevertheless, it is imperative to sustain infection control measures and monitoring protocols, particularly for high-risk demographics such as the elderly and individuals in high-risk facilities.

This study has some limitations. First, since the data were extracted according to the definition of the criteria for the dominance period depending on the COVID-19 variant, some periods were excluded from the analyzed data. Therefore, there is a possibility that the results may change depending on the reclassification of dominance period criteria. In addition, the case fatality rate of Omicron is one-fourth of that of the Delta variant, and upon completion of vaccination, the case fatality rate of Omicron is reported to be similar to or lower than that of seasonal flu [25]. However, since comparative analysis depending on vaccination status was not conducted in this report, further analysis of the case severity rate and case fatality rates depending on vaccination is necessary.

As the COVID-19 management system has transitioned and the quarantine management level has been lowered, many aspects are shifting toward self-regulation. However, intensive protection and management are still required for the older adults and high-risk groups. Prompt and proactive treatment should be provided to ensure that the condition do not progress to severe stages. In addition, many people’s capacity to follow quarantine rules has been strengthened due to the pandemic. Thus, even as epidemic control measures are further relaxed and COVID-19 is changed from the Class 2 national notifiable infectious disease to the Class 4 infectious disease, there is a need to promote citizen culture of adhering to voluntarily daily hygiene practices such as handwashing, cough etiquette, regular ventilation, and disinfection, as these habits have been reinforced through the pandemic.

Ethics Statement: Not applicable.

Funding Source: None.

Acknowledgments: None.

Conflict of Interest: The authors have no conflicts of interest to declare.

Author Contributions: Conceptualization: SJJ, BYR, SYP, SSK. Data curation: SJJ, MSA, MJJ, SYC, YJC, JHJ, BYR, SYP, SSK. Formal analysis: SJJ. Methodology: SJJ, BYR, SYP, SSK. Resources: SJJ, MSA, MJJ, SYC, YJC, JHJ. Visualization: SJJ. Writing - original draft: SJJ. Writing - review & editing: SJJ, BYR, SYP, SSK.

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Surveillance Reports

Public Health Weekly Report 2023; 16(43): 1464-1487

Published online November 9, 2023 https://doi.org/10.56786/PHWR.2023.16.43.2

Copyright © The Korea Disease Control and Prevention Agency.

Severity of COVID-19 Associated with SARS-CoV-2 Variants Dominant Period in the Republic of Korea

Se-Jin Jeong1, Misuk An1, Minjeong Jang1, So Young Choi1,2, You-Jung Choi1, Jinhwa Jang1,2, Boyeong Ryu1,2, Shin Young Park1,2, Seong-Sun Kim1,2*

1Data Analysis Team, Epidemiological Investigation and Analysis Task Force, Central Disease Control Headquarters, Korea Disease Control and Prevention Agency (KDCA), Cheongju, Korea,
2Division of Public Health Emergency Response Research, Korea Disease Control and Prevention Agency (KDCA), Cheongju, Korea

Correspondence to:*Corresponding author: Seong-Sun Kim, Tel: +82-43-719-7730, E-mail: sskim0719@korea.kr

Received: September 1, 2023; Revised: September 13, 2023; Accepted: September 25, 2023

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

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.

Keywords: COVID-19, SARS-CoV-2, COVID-19 severity, COVID-19 variants, COVID-19 deaths

Body

Key messages

① What is known previously?

The severity of COVID-19 in Republic of Korea decreased during the Delta dominance period, despite the increase in delta variant-specific severity, and continued to decrease during the omicron dominance period.

② What new information is presented?

Peak case severity and case fatality rate were in the Pre- Delta dominance period (2020.1.20.–2022.7.24., 2.98% and 1.15%), lowest during Omicron XBB dominance period (2023.4.16.–2023.7.31., 0.12% and 0.04%).

③ What are implications?

As new COVID-19 variants emerge, Omicron XBB had a 0.04% case severity rate, lower than seasonal influenza. However, case fatality rate in the 80+ group remain high, underlining the importance of prioritizing high-risk individuals.

Introduction

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While most people infected with this virus experience mild to moderate respiratory diseases and can recover without special treatment, certain groups such as older adults and those with underlying conditions such as cardiovascular disease, diabetes, or chronic respiratory disease require medical attention [1]. As of August 2, 2023, the World Health Organization (WHO) reported a global total of 768,983,095 confirmed cases with 11,740,993 deaths and a case fatality rate of 1.0%. A total of 13,492,099,754 vaccine doses were administered worldwide. In the Republic of Korea (ROK), during the same period, there were 33,322,073 confirmed cases and 35,339 deaths, with a case fatality rate of 0.11%. In comparison, seasonal influenza, a respiratory infection similar to COVID-19, had an incidence rate of 16.9 per 1,000 outpatients as of July 25, 2023 [2], with a case fatality rate of 0.03–0.07% globally and 0.03–0.08% in the ROK according to the WHO [3]. Furthermore, in terms of the primary vaccination, 44,327,956 individuals have received vaccination, indicating a vaccination rate of 86.7% relative to the national population [4].

SARS-CoV-2 undergoes mutations as it spreads across various countries and infects new hosts over time [5]. While these mutations may not significantly alter the properties of the virus, they can impact public health and societal aspects such as transmission, disease severity, vaccine effectiveness, and therapeutics [6].

The WHO classified variant viruses into variants of interest (VOI) and variants of concern (VOC) to prioritize research and monitoring of these strains. Accordingly, the WHO is implementing ‘SARS-CoV-2 variant tracking monitoring,’ and the U.S. Centers for Disease Control and Prevention is implementing the ‘National SARS-CoV-2 Genomic Surveillance System,’ ‘National Wastewater Surveillance System,’ and ‘Traveler-based SARS-CoV-2 Genomic Surveillance program’ [6,7]. ROK also actively is monitoring them according to the variant virus classification system [8]. The VOC were designated and managed in the following order: the Alpha and Beta variants in December 2020, the Gamma variant in January 2021, the Delta variant in May 2021, and the Omicron variant in November 2021 [9]. Over time, the COVID-19 virus has shown increasing diversity, with dominant strains having lower severity and reduced infection risk due to vaccination [10,-12]. Notably, the Omicron variant exhibits higher transmissibility and reduced hospitalization periods by 15–20%, with a 41% (95% confidence interval: 37–45%) decrease in the risk of hospitalization lasting one or more nights, depending on vaccination status [13]. As of August 2023, the number of confirmed COVID-19 cases and deaths has decreased worldwide, with no emergence of new highly pathogenic or contagious new variants reported [14].

Therefore, this study aims to assess the occurrence and current status of patients with severe or critical conditions and deaths in the ROK during the dominance of SARS-CoV-2 variants. By comparing the rates of case severity and case fatality, this research intends to contribute fundamental data to prioritize and define the scope for future COVID-19 management adjustments, particularly in terms of infectious disease classification. The findings will serve as fundamental data for planning healthcare resource allocation.

Methods

1. Study Population

We included individuals with confirmed COVID-19 reported to the COVID-19 Information Management System of the Korea Disease Control and Prevention Agency (KDCA) from January 20, 2020 to July 31, 2023; the scale of the occurrence and demographic characteristics of those whose condition progressed to critical condition or those who died were analyzed separately during the entire period following the dominance periods of COVID-19 virus variants. A patient with confirmed COVID-19 was defined as a person whose disease status was determined by genetic tests of the virus or whose infection was confirmed by isolating the virus regardless of clinical symptoms or a person who showed symptoms of COVID-19 whereby the infection was confirmed with a rapid antigen (for professional use/implemented on March 14, 2022) or emergency screening tests. Severe COVID-19 cases were classified as those who, after COVID-19 confirmation, received non-invasive ventilation, high-flow oxygen therapy, invasive ventilation, multi-organ failure, extracorporeal membrane oxygenation, or continuous renal replacement therapy while quarantined in a medical institution [15]. The clinical condition of confirmed patients was monitored based on data and telephone communication reported to the ‘COVID-19 Information Management System’ (KDCA) and the ‘Health and Medical Resources Integrated Reporting Portal System’ (Central Disaster Management Headquarters). Information on COVID-19 deaths was collected from individuals reported through the Integrated Disease and Health Management System of the KDCA according to the “Infectious Disease Control and Prevention Act.” The study focused on COVID-19-related deaths, excluding cases of foreign nationals.

2. Data Analysis

To understand the scale and characteristics of the occurrence of severe and critical patients and deaths, demographic characteristics, including sex and age, incidence status by reported area according to the epidemic periods, were calculated based on the date of diagnosis confirmation. In addition, the severity of COVID-19 was categorized into two stages to assess the impact of viral mutations on disease severity, and we calculated the case severity rate and case fatality rates for both the entire epidemic period and by weeks.

The dominance period was classified based on the week in which more than 50% of the weekly variant virus tests detected the VOI, according to the SARS-CoV-2 variant analysis report date. Of the entire period, the dominance period was divided into the Delta variant (reported from July 25, 2021–January 15, 2022), the Omicron BA.1 and BA.2 variant (January 16, 2022–July 9, 2022), the Omicron BA.5 variant (July 24, 2022–December 31, 2022), the Omicron BN.1 variant (January 22, 2023–March 25, 2023), and the Omicron XBB variant (April 16, 2023–July 31, 2023) dominance periods, and cases reported at times not included in the dominance periods were excluded from the analysis. In addition, since no sublineages of the Omicron XBB with an occupancy rate of 30% or higher have been confirmed to date [16], we analyzed the Omicron XBB variant period as a whole. The case severity rate was calculated as the proportion (%) of patients with severe or critical conditions and deaths among confirmed cases reported in the relevant period (dominance period of the virus’ variants), and the case fatality rate was calculated as the proportion (%) of deaths among confirmed cases occurring in the relevant period (the virus’ variant dominance period). In addition, to calculate the scale of deaths per 100,000 population relative to the total population (mortality rate), resident registration central population data (population distribution representing the relevant year) registered with Statistics Korea were used [17], and the case severity rate, case fatality, and mortality rates were stratified by dividing age groups into 10-year increments to compare severity by age. We used the Microsoft Excel 2018 (Microsoft) and Tableau ver. 2021.4 (Salesforce) for all of the analysis.

Results

Since the COVID-19 outbreak, a total of 34,082,179 confirmed cases had been reported until July 31, 2023. Compared to the total number of confirmed cases of 34,082,179, the period before the dominant prevalence of the Delta variant had 0.5% (187,340 cases) of confirmed cases, the Delta variant had 1.5% (500,414 cases), and the Omicron variants had 52.2% (17,800,369 cases) for BA.1 and BA.2, 29.1% (9,912,503 cases) for BA.5, 2.3% (777,942 cases) for BN.1, and 6.5% (2,224,486 cases) for XBB. Among all confirmed cases, the condition in a total of 63,522 cases (0.19%) progressed to severe conditions or death during the entire study period. Of these, 37,760 cases (0.11%) were classified as patients with severe or critical conditions, and 35,644 cases (0.11%) deceased. Among patients whose condition progressed to severe conditions after a COVID-19 diagnosis, 9,882 cases (0.03%) eventually died.

1. Status of Patients with Severe or Critical Conditions

A total of 37,760 patients with severe or critical conditions were identified during the COVID-19 outbreak. The period in which the most patients with severe or critical conditions occurred by variant dominance period was when the Omicron variants BA.1 and BA.2 were dominant, accounting for the highest occurrence of patients with severe or critical conditions at 27.7% (10,460 cases) (Table 1). Following that, during the Omicron BA.5 dominance period, 23.0% (8,675 cases) patients with severe or critical conditions were reported. Comparing the Omicron BA.1 and BA.2 dominance period to the Delta variant dominance period, a significant increase (35.6-fold) was noted in the number of confirmed cases, which also led to a 1.3-fold increase in patients with severe or critical conditions. However, due to the reduced severity associated with Omicron, the increase in patients with severe or critical conditions during this period remained at a lower level (Figure 1). Regarding sex distribution, the proportion of men in the entire period was 57.7%, which was 15.4%p higher than that of women. The average age of patients in patients with severe or critical conditions was 72.3 years (standard deviation [SD]±15.7 years), showing a gradual increase in average age from the Pre-Delta variant dominance period at 67.7 years (SD±13.7 years) and the Delta variant dominance period at 66.1 years (SD±15.4 years) to the Omicron BA.1/2 dominance period at 72.7 years (SD±15.7 years) and the Omicron BA.5 dominance period at 75.0 years (SD±15.4 years). In terms of age groups, those aged 60 years and above accounted for the highest proportion, with 30,866 cases (81.7%). Among this age group, during the Omicron BA.5 dominance period, the proportion reached 88.1%, the highest of all periods. Following that, during the Omicron XBB dominance period, it was 87.1%. Notably, the age group of 80 years and above, which accounted for 19.6% during the Delta variant dominance period, increased by approximately 2.1-fold to an average of 42.3% during the Omicron period. Regarding area distribution, the metropolitan area (Seoul, Gyeonggi, Incheon) accounted for more than half, at 61.9% (23,347 cases), throughout the entire period, while non-metropolitan area contributed 37.8% (14,287 cases). Based on reporting areas, Seoul reported the highest number of cases at 10,337 (27.4%), followed by Gyeonggi with 10,183 cases (27.0%). When analyzed by dominant variant periods, the metropolitan area reported the highest proportions in both the Pre-Delta variant dominance period (72.9%) and the Delta variant dominance period (74.5%). In addition, during the Omicron XBB dominance period, non-metropolitan areas accounted for over half (54.0%) of the cases. However, during other variant periods, the majority of cases were reported in the metropolitan area (Delta: 74.5%; BA.1, BA.2: 57.1%; BA.5: 57.2%; BN.1: 52.2%). In particular, among the 126 cases reported in quarantine, the Pre-Delta variant dominance period had the highest count at 97 cases (2.1%), followed by the Delta variant dominance period with 27 cases (0.3%).

Figure 1. Weekly number of confirmed cases, severe/critical cases and deaths (as of July 31, 2023)

Characteristics of COVID-19b) severe/critical casesa) by period (as of as of July 31, 2023)
ClassVariants dominant period
Total (2020.1.20.-2023.7.31.)Pre-Delta (2020.1.20.-2021.7.24.)Delta dominant period (2021.7.25.-2022.1.15.)Omicron dominant period
BA.1/BA.2 (2022.1.16.-2022.7.9.)BA.5 (2022.7.24.-2022.12.31.)BN.1 (2023.1.22.-2023.3.25.)XBB (2023.4.16.-2023.7.31.)
Total37,760 (100.0)4,665 (100.0)8,296 (100.0)10,460 (100.0)8,675 (100.0)1,364 (100.0)2,028 (100.0)
Sex
Male21,787 (57.7)2,792 (59.8)4,775 (57.6)6,029 (57.6)4,886 (56.3)811 (59.5)1,199 (59.1)
Female15,973 (42.3)1,873 (40.2)3,521 (42.4)4,431 (42.4)3,789 (43.7)553 (40.5)829 (40.9)
Age (yr)
Average±standard deviation72.3±15.767.7±13.766.1±15.472.7±15.775.0±15.473.6±15.673.6±15.5
0-9209 (0.6)0 (0.0)6 (0.1)74 (0.7)67 (0.8)12 (0.9)25 (1.2)
10-19158 (0.4)3 (0.1)21 (0.2)65 (0.6)47 (0.5)7 (0.5)5 (0.3)
20-29385 (1.0)44 (0.9)129 (1.6)108 (1.0)63 (0.7)13 (1.0)11 (0.5)
30-39899 (2.4)116 (2.5)399 (4.8)193 (1.9)112 (1.3)20 (1.5)28 (1.4)
40-491,694 (4.5)298 (6.4)664 (8.0)343 (3.3)241 (2.8)39 (2.8)51 (2.5)
50-593,549 (9.4)730 (15.6)1,150 (13.9)777 (7.4)506 (5.8)93 (6.8)141 (7.0)
60-697,821 (20.7)1,240 (26.6)2,218 (26.7)2,045 (19.6)1,315 (15.2)225 (16.5)379 (18.7)
70-799,968 (26.4)1,289 (27.6)2,084 (25.1)2,805 (26.8)2,242 (25.8)396 (29.0)532 (26.2)
≥8013,077 (34.6)945 (20.3)1,625 (19.6)4,050 (38.7)4,082 (47.1)559 (41.0)856 (42.2)
≥6030,866 (81.7)3,474 (74.5)5,927 (71.4)8,900 (85.1)7,639 (88.1)1,180 (86.5)1,767 (87.1)
Region
Metropolitan area23,347 (61.9)3,402 (72.9)6,184 (74.5)5,975 (57.1)4,960 (57.2)713 (52.2)932 (46.0)
Seoul10,337 (27.4)1,876 (40.2)3,348 (40.3)2,275 (21.7)1,707 (19.7)276 (20.2)412 (20.3)
Gyeonggi10,183 (27.0)1,238 (26.5)2,255 (27.2)2,746 (26.3)2,589 (29.8)359 (26.3)420 (20.7)
Incheon2,827 (7.5)288 (6.2)581 (7.0)954 (9.1)664 (7.7)78 (5.7)100 (5.0)
Non-metropolitan area14,287 (37.8)1,166 (25.0)2,085 (25.2)4,484 (42.9)3,714 (42.8)651 (47.8)1,096 (54.0)
Busan2,347 (6.2)156 (3.3)433 (5.2)723 (6.9)566 (6.5)108 (7.9)189 (9.3)
Deagu1,806 (4.8)240 (5.1)258 (3.1)613 (5.9)412 (4.7)54 (4.0)130 (6.4)
Gwangju811 (2.2)65 (1.4)70 (0.9)301 (2.9)229 (2.6)29 (2.1)47 (2.3)
Daejeon883 (2.3)71 (1.5)168 (2.0)269 (2.6)209 (2.4)36 (2.6)61 (3.0)
Ulsan660 (1.8)75 (1.6)99 (1.2)196 (1.9)177 (2.0)23 (1.7)43 (2.1)
Sejong82 (0.2)2 (0.0)12 (0.2)31 (0.3)23 (0.3)3 (0.2)4 (0.2)
Gangwon1,338 (3.5)99 (2.1)175 (2.1)444 (4.2)361 (4.2)65 (4.8)95 (4.7)
Chungbuk754 (2.0)64 (1.4)138 (1.7)265 (2.5)172 (2.0)32 (2.4)41 (2.0)
Chungnam1,486 (3.9)97 (2.1)226 (2.7)395 (3.8)470 (5.4)61 (4.5)115 (5.7)
Jeonbuk711 (1.9)58 (1.2)81 (1.0)247 (2.4)183 (2.1)33 (2.4)54 (2.7)
Jeonnam758 (2.0)42 (0.9)63 (0.8)239 (2.3)205 (2.4)43 (3.2)88 (4.3)
Gyeongbuk1,020 (2.7)94 (2.0)100 (1.2)274 (2.6)311 (3.6)69 (5.1)77 (3.8)
Gyeongnam1,403 (3.7)88 (1.9)235 (2.8)404 (3.9)370 (4.3)81 (5.9)109 (5.4)
Jeju228 (0.6)15 (0.3)27 (0.3)83 (0.8)26 (0.3)14 (1.0)43 (2.1)
Quarantine126 (0.3)97 (2.1)27 (0.3)1 (0.0)1 (0.0)0 (0.0)0 (0.0)

Unit: n (%). a)Severe/critical case: Patient who were treated with non-invasive ventilation, high flow oxygenation, invasive ventilation, extracorporeal membrane oxygenation, continuous renal replacement treatment during quarantine from coronavirus disease 2019. b)Number of confirmed cases (≥80): Pre-Delta dominant period 187,340 (6,083, 3.2%), Delta dominant period 500,414 (15,600, 3.1%), Omicron BA.1/BA.2 dominant period 17,800,369 (516,128, 2.9%), Omicron BA.5 dominant period 9,912,503 (411,067, 4.1%), Omicron BN.1 dominant period 777,942 (42,126, 5.4%), Omicron XBB dominant period 2,224,486 (112,926, 5.1%)..



2. Deaths

Among the total 35,644 deaths reported during the entire COVID-19 pandemic period, the majority, 52.4% (18,679 cases), occurred during the Omicron BA.1 and BA.2 dominance period (Table 2). During the Omicron BA.1 and BA.2 dominance period, there was a simultaneous increase in confirmed cases (35.6-fold) and deaths (3.9-fold). However, in terms of severity, compared to the increase in confirmed cases during the Omicron dominance period, the rise in deaths remained at a lower level (Figure 1). Regarding sex distribution of patients, 50.6% (18,029 cases) were women and 49.4% (17,615 cases) were men. However, except for the Omicron BA.1 and BA.2 dominance period, in other variant periods, males had a higher mortality rate than females, as indicated by a majority of deaths. The overall average age was 79.2 years (SD±12.2 years), that for the period of the dominant prevalence of the Pre-Delta variant was 78.4 years (SD±11.4 years), the Delta variant dominance period was 77.2 years (SD±12.2 years), the Omicron BA.1 and BA.2 dominance period was 80.4 years (SD±12.1 years), the Omicron BA.5 dominance period was 80.2 years (SD±12.2 years), BN.1 dominance period was 78.8 years (SD±12.7 years), and XBB was 80.4 years (SD±11.9 years), which meant deaths were found to generally be within the age range of 70s to 80s. Exploring the different age groups, excluding 48.0% (2,292 cases) of the people of the Delta variant dominance period, the proportion of people aged 80 or older was more than half in the period before the dominant prevalence of the Pre-Delta variant (52.4%) and all the Omicron variants dominance periods (58.2% to 63.8%), and people over 60 age group accounted for more than 90% of the total age (92.4% to 95.3%). Regarding area distribution, more than half of the deaths occurred in non-metropolitan areas at 51.7% (18,443 cases) during the entire period, whereas those in the metropolitan area accounted for 48.2% (17,185 cases). Based on reporting areas, Gyeonggi had the highest number of deaths, with 8,586 (24.1%), followed by Seoul with 6,638 (18.6%). When divided by period for each variant, more than half of the deaths occurred in the metropolitan area in the pre-Delta and the Delta dominance periods, at 61.8% and 74.3%, respectively, and in other variant periods, more than half of the deaths occurred in non-metropolitan areas (BA.1, BA.2: 56.9%; BA.5: 56.6%; BN.1: 63.0%; XBB: 59.0%).

Characteristics of coronavirus disease 2019 deaths by period (as of July 31, 2023)
ClassVariants dominant period
Total (2020.1.20.-2023.7.31.)Pre-Delta (2020.1.20.-2021.7.24.)Delta dominant period (2021.7.25.-2022.1.15.)Omicron dominant period
BA.1/BA.2 (2022.1.16.-2022.7.9.)BA.5 (2022.7.24.-2022.12.31.)BN.1 (2023.1.22.-2023.3.25.)XBB (2023.4.16.-2023.7.31.)
Total35,644 (100.0)2,163 (100.0)4,772 (100.0)18,679 (100.0)6,838 (100.0)809 (100.0)984 (100.0)
Sex
Male17,615 (49.4)1,091 (50.4)2,487 (52.1)8,881 (47.5)3,455 (50.5)444 (54.9)527 (53.6)
Female18,029 (50.6)1,072 (49.6)2,285 (47.9)9,798 (52.5)3,383 (49.5)365 (45.1)457 (46.4)
Age (yr)
Average±standard deviation79.2±12.278.4±11.477.2±12.280.4±12.180.2±12.278.8±12.780.4±11.9
0-939 (0.1)0 (0.0)3 (0.1)21 (0.1)10 (0.1)0 (0.0)2 (0.2)
10-1924 (0.1)0 (0.0)0 (0.0)13 (0.1)6 (0.1)3 (0.4)1 (0.1)
20-2981 (0.2)5 (0.2)10 (0.2)48 (0.3)15 (0.2)0 (0.0)1 (0.1)
30-39166 (0.5)11 (0.5)33 (0.7)70 (0.4)33 (0.5)8 (1.0)5 (0.5)
40-49480 (1.3)20 (0.9)79 (1.7)242 (1.3)94 (1.4)12 (1.5)10 (1.0)
50-591,446 (4.1)105 (4.9)233 (4.9)708 (3.8)269 (3.9)38 (4.7)28 (2.8)
60-694,044 (11.3)284 (13.1)822 (17.2)1,897 (10.1)684 (10.0)99 (12.2)103 (10.6)
70-798,065 (22.6)604 (28.0)1,300 (27.2)4,001 (21.4)1,476 (21.6)178 (22.0)206 (20.9)
≥8021,299 (59.8)1,134 (52.4)2,292 (48.0)11,679 (62.5)4,251 (62.2)471 (58.2)628 (63.8)
≥6033,408 (93.7)2,022 (93.5)4,414 (92.4)17,577 (94.0)6,411 (93.8)748 (92.4)937 (95.3)
Region
Metropolitan area17,185 (48.2)1,337 (61.8)3,544 (74.3)8,048 (43.1)2,971 (43.4)299 (37.0)403 (41.0)
Seoul6,638 (18.6)555 (25.7)1,717 (36.0)2,719 (14.6)1,105 (16.1)117 (14.5)193 (19.6)
Gyeonggi8,586 (24.1)714 (33.0)1,541 (32.3)4,244 (22.7)1,526 (22.3)131 (16.2)158 (16.1)
Incheon1,961 (5.5)68 (3.1)286 (6.0)1,085 (5.8)340 (5.0)51 (6.3)52 (5.3)
Non-metropolitan area18,443 (51.7)814 (37.6)1,224 (25.6)10,631 (56.9)3,867 (56.6)510 (63.0)581 (59.0)
Busan2,926 (8.2)130 (6.0)245 (5.1)1,878 (10.1)441 (6.4)44 (5.4)80 (8.1)
Deagu2,061 (5.8)222 (10.3)166 (3.5)1,026 (5.5)453 (6.6)56 (6.9)51 (5.2)
Gwangju858 (2.4)24 (1.1)48 (1.0)536 (2.9)172 (2.5)19 (2.3)19 (1.9)
Daejeon991 (2.8)34 (1.6)157 (3.3)529 (2.8)169 (2.5)32 (4.0)29 (2.9)
Ulsan544 (1.5)40 (1.8)28 (0.6)314 (1.7)116 (1.7)11 (1.4)13 (1.3)
Sejong59 (0.2)1 (0.0)3 (0.1)32 (0.2)12 (0.2)1 (0.1)3 (0.3)
Gangwon1,388 (3.9)56 (2.6)65 (1.4)769 (4.1)346 (5.1)36 (4.5)54 (5.5)
Chungbuk1,087 (3.0)71 (3.3)55 (1.2)629 (3.4)218 (3.2)28 (3.5)34 (3.5)
Chungnam1,635 (4.6)46 (2.1)139 (2.9)896 (4.8)413 (6.0)38 (4.7)40 (4.1)
Jeonbuk1,270 (3.6)60 (2.8)65 (1.4)802 (4.3)223 (3.3)35 (4.3)28 (2.8)
Jeonnam1,071 (3.0)18 (0.8)30 (0.6)548 (2.9)309 (4.5)53 (6.5)61 (6.2)
Gyeongbuk2,161 (6.1)88 (4.1)114 (2.4)1,301 (7.0)463 (6.8)52 (6.4)51 (5.2)
Gyeongnam2,077 (5.8)23 (1.1)97 (2.0)1,196 (6.4)476 (7.0)97 (12.0)85 (8.6)
Jeju315 (0.9)1 (0.0)12 (0.3)175 (0.9)56 (0.8)8 (1.0)33 (3.4)
Quarantine16 (0.0)12 (0.6)4 (0.1)0 (0.0)0 (0.0)0 (0.0)0 (0.0)

Unit: n (%)..



3. Trends in Case Severity and Fatality Rates

During the entire pandemic, the case severity rate was 0.19%, and the case fatality rate was 0.10%. In terms of different epidemic periods, the case severity rate and case fatality rates were the highest at 2.98% and 1.15%, respectively, in the pre-Delta dominance period, followed by the case severity rate and case fatality rates at 2.14% and 0.95%, respectively, in the Delta dominance period. The case severity rate and case fatality rates were the lowest at 0.12% and 0.04%, respectively, in the Omicron XBB dominance period (Table 3, Figure 2). The case severity rate decreased from 2.98% in the pre-Delta dominance period to 0.14% in the Omicron BA.5 dominance period. However, it increased in the Omicron BN.1 dominance period (0.25%) and then showed a trend of decreasing again to 0.12% in the Omicron XBB dominance period. The case fatality rate was also the highest in the pre-Delta variant dominance period at 1.15% and showed a decreasing trend until the Omicron BA.5 dominance period (0.07%). However, there was an increase (0.10%) during the Omicron BN.1 dominance period, followed by another decline (0.04%) during the Omicron XBB dominance period. Compared to the Delta variant dominance period, the Omicron XBB dominance period experienced a significant reduction in case fatality rates, amounting to a 29-fold decrease.

Figure 2. Weekly case severity rate and case fatality rate (as of July 31, 2023)

Case severity rate and case fatality rate by variant dominant period (as of July 31, 2023)
ClassVariants dominant period
Total (2020.1.20.-2023.7.31.)Pre-Delta (2020.1.20.-2021.7.24.)Delta dominant period (2021.7.25.-2022.1.15.)Omicron dominant period
BA.1/BA.2 (2022.1.16.-2022.7.9.)BA.5 (2022.7.24.-2022.12.31.)BN.1 (2023.1.22.-2023.3.25.)XBB (2023.4.16.-2023.7.31.)
Case severity rate (yr)a)0.192.982.140.150.140.250.12
0-90.010.000.02<0.010.010.030.03
10-19<0.010.020.04<0.01<0.010.01<0.01
20-290.010.150.190.010.010.01<0.01
30-390.020.450.560.010.010.020.01
40-490.041.040.980.020.020.040.02
50-590.102.261.910.060.050.110.05
60-690.275.313.590.190.140.300.15
70-790.7513.638.880.700.470.870.34
≥802.4225.4219.752.731.742.131.18
Case fatality rate (yr)b)0.101.150.950.100.070.100.04
0-9<0.010.000.01<0.01<0.010.00<0.01
10-19<0.010.000.00<0.01<0.01<0.01<0.01
20-29<0.010.020.01<0.01<0.010.00<0.01
30-39<0.010.040.04<0.01<0.010.01<0.01
40-490.010.070.110.010.010.01<0.01
50-590.030.310.360.030.020.040.01
60-690.111.141.170.110.060.100.03
70-790.405.594.420.470.220.300.11
≥801.7418.6414.692.261.031.120.56
Mortality rate (per 1,000,000) (yr)69.294.209.2836.3113.291.571.91
0-91.100.000.080.590.280.000.06
10-190.510.000.000.280.130.060.02
20-291.260.080.160.750.230.000.02
30-392.510.170.501.060.500.120.08
40-495.950.250.983.001.160.150.12
50-5916.791.222.718.223.120.440.33
60-6954.623.8411.1025.629.241.341.39
70-79210.8115.7933.98104.5838.584.655.38
≥80944.0750.26101.59517.67188.4220.8827.84

Unit: %. a)Case severity rate: (number of severe/critical cases and deaths among confirmed cases in specific period)/number of confirmed cases in specific period×100. b)Case fatality rate: (number of deaths among confirmed cases in specific period)/number of confirmed cases in specific period×100..



The case severity rate, case fatality, and mortality rates according to age in each period all increased with advancing age. Across different age groups, as the epidemic transitioned from the Delta variant dominance period to the Omicron BA.1/2 dominance period, a decreasing trend in case severity rate and case fatality rates was observed for all age groups. The age group with the most substantial relative reduction in case severity rate during this transition was the 30s (from 0.56% to 0.01%, a 60.3-fold decrease), followed by the 40s (from 0.98% to 0.02%, a 32.9-fold decrease). The age group with the least relative decrease was the 80s (from 19.75% to 2.73%, a 7.2-fold decrease). A similar pattern was observed in the age-specific case fatality rates, with the 30s (0.04% to <0.01%, a 16.8-fold decrease) experiencing the most substantial relative decrease and the 80s (14.69% to 2.26%, a 6.5-fold decrease) having the least relative decrease. During the Omicron BA.5 and BN.1 dominance periods, all age groups except the over 80s had case severity and case fatality rates below 1%. During the Omicron XBB dominance period, except for a case severity rate of 1.18% in the over 80 age group, all other age groups had exhibited case severity rate and case fatality rates below 1%.

The mortality rate reached its highest at 36.31 deaths per 100,000 people during the Omicron BA.1/2 dominance period, characterized by a sharp increase in confirmed cases nationwide, followed by the Omicron BA.5 dominance period with a rate of 13.29 deaths per 100,000 people. For the over 80 age group, the mortality rate was 944.07 deaths per 100,000 people. In addition, when classified by the dominance period, the mortality rate was maintained at more than 100 per 100,000 population in the Delta variant, Omicron BA.1/2, and Omicron BA.5 dominance periods, while the Pre-Delta variant dominance period had a rate of 50.26, the Omicron BN.1 dominance period had a rate of 20.88, and the Omicron XBB dominance period had a rate of 27.84, all showing a declining trend.

Conclusion

Following a previous report [18] that analyzed the case severity rate trend from the date of the first confirmed case of COVID-19 in the ROK to the Omicron BA.5 dominance period, this report compared and analyzed the severity trends until the Omicron XBB dominance period. The average incubation period of the Omicron variant is 4.2 days (range: 2–8 days), which is shorter than that of the Delta variant at 5.8 days. The Omicron variant is reported to have a higher transmissibility of infection than other variants such as the Delta variant due to increased antibody evasion [19]. In addition, when exploring each epidemic period, the case severity rate and case fatality rates in the Delta variant dominance period were 2.14% and 0.95%, respectively, and the case severity rate and case fatality rates in the Omicron XBB dominance period were 0.12%, and 0.04%, respectively, showing that the number of infected cases increased rapidly through the Omicron variant, but with decreasing severity levels. This aligns with prior research, which has indicated that the Omicron variant is associated with milder symptoms and reduced severity in comparison to other variants [20,21]. Reflecting this decreasing trend of lower case severity rate and case fatality rates, the Central Disaster Management Headquarters lowered the COVID-19 crisis level from ‘severe’ to ‘alert’ as from June 1, 2023 [22]. However, it is important to note that the number of confirmed cases has continued to increase since the Omicron XBB dominance period from March 2023 to July 2023. This can be attributed to the highly transmissible nature of the Omicron XBB variant and the effects of the crisis-level adjustment. Nevertheless, case severity rate, case fatality rates, and mortality rates have been gradually decreasing during these periods. However, there are age-specific variations in case severity rate and case fatality rates, with the over 80 age group being the least affected. The most significant disparities were observed in the 20s and 30s age groups. This aligns with the trend of decreasing disparities with increasing age (Table 3), potentially related to the impact of age on the immune system [23] and research indicating reduced vaccine efficacy among those over 65 age group [24]. Additionally, the case fatality rate (0.04%) during the ongoing Omicron XBB dominance period is at the level of the case fatality rate of seasonal influenza (0.03% to 0.08%), which is lower than that of other variant dominance periods [3]. This indicates a diminished disease risk and implies the potential for a gradual relaxation of epidemic control measures. Nevertheless, it is imperative to sustain infection control measures and monitoring protocols, particularly for high-risk demographics such as the elderly and individuals in high-risk facilities.

This study has some limitations. First, since the data were extracted according to the definition of the criteria for the dominance period depending on the COVID-19 variant, some periods were excluded from the analyzed data. Therefore, there is a possibility that the results may change depending on the reclassification of dominance period criteria. In addition, the case fatality rate of Omicron is one-fourth of that of the Delta variant, and upon completion of vaccination, the case fatality rate of Omicron is reported to be similar to or lower than that of seasonal flu [25]. However, since comparative analysis depending on vaccination status was not conducted in this report, further analysis of the case severity rate and case fatality rates depending on vaccination is necessary.

As the COVID-19 management system has transitioned and the quarantine management level has been lowered, many aspects are shifting toward self-regulation. However, intensive protection and management are still required for the older adults and high-risk groups. Prompt and proactive treatment should be provided to ensure that the condition do not progress to severe stages. In addition, many people’s capacity to follow quarantine rules has been strengthened due to the pandemic. Thus, even as epidemic control measures are further relaxed and COVID-19 is changed from the Class 2 national notifiable infectious disease to the Class 4 infectious disease, there is a need to promote citizen culture of adhering to voluntarily daily hygiene practices such as handwashing, cough etiquette, regular ventilation, and disinfection, as these habits have been reinforced through the pandemic.

Declarations

Ethics Statement: Not applicable.

Funding Source: None.

Acknowledgments: None.

Conflict of Interest: The authors have no conflicts of interest to declare.

Author Contributions: Conceptualization: SJJ, BYR, SYP, SSK. Data curation: SJJ, MSA, MJJ, SYC, YJC, JHJ, BYR, SYP, SSK. Formal analysis: SJJ. Methodology: SJJ, BYR, SYP, SSK. Resources: SJJ, MSA, MJJ, SYC, YJC, JHJ. Visualization: SJJ. Writing - original draft: SJJ. Writing - review & editing: SJJ, BYR, SYP, SSK.

Fig 1.

Figure 1.Weekly number of confirmed cases, severe/critical cases and deaths (as of July 31, 2023)
Public Health Weekly Report 2023; 16: 1464-1487https://doi.org/10.56786/PHWR.2023.16.43.2

Fig 2.

Figure 2.Weekly case severity rate and case fatality rate (as of July 31, 2023)
Public Health Weekly Report 2023; 16: 1464-1487https://doi.org/10.56786/PHWR.2023.16.43.2
Characteristics of COVID-19b) severe/critical casesa) by period (as of as of July 31, 2023)
ClassVariants dominant period
Total (2020.1.20.-2023.7.31.)Pre-Delta (2020.1.20.-2021.7.24.)Delta dominant period (2021.7.25.-2022.1.15.)Omicron dominant period
BA.1/BA.2 (2022.1.16.-2022.7.9.)BA.5 (2022.7.24.-2022.12.31.)BN.1 (2023.1.22.-2023.3.25.)XBB (2023.4.16.-2023.7.31.)
Total37,760 (100.0)4,665 (100.0)8,296 (100.0)10,460 (100.0)8,675 (100.0)1,364 (100.0)2,028 (100.0)
Sex
Male21,787 (57.7)2,792 (59.8)4,775 (57.6)6,029 (57.6)4,886 (56.3)811 (59.5)1,199 (59.1)
Female15,973 (42.3)1,873 (40.2)3,521 (42.4)4,431 (42.4)3,789 (43.7)553 (40.5)829 (40.9)
Age (yr)
Average±standard deviation72.3±15.767.7±13.766.1±15.472.7±15.775.0±15.473.6±15.673.6±15.5
0-9209 (0.6)0 (0.0)6 (0.1)74 (0.7)67 (0.8)12 (0.9)25 (1.2)
10-19158 (0.4)3 (0.1)21 (0.2)65 (0.6)47 (0.5)7 (0.5)5 (0.3)
20-29385 (1.0)44 (0.9)129 (1.6)108 (1.0)63 (0.7)13 (1.0)11 (0.5)
30-39899 (2.4)116 (2.5)399 (4.8)193 (1.9)112 (1.3)20 (1.5)28 (1.4)
40-491,694 (4.5)298 (6.4)664 (8.0)343 (3.3)241 (2.8)39 (2.8)51 (2.5)
50-593,549 (9.4)730 (15.6)1,150 (13.9)777 (7.4)506 (5.8)93 (6.8)141 (7.0)
60-697,821 (20.7)1,240 (26.6)2,218 (26.7)2,045 (19.6)1,315 (15.2)225 (16.5)379 (18.7)
70-799,968 (26.4)1,289 (27.6)2,084 (25.1)2,805 (26.8)2,242 (25.8)396 (29.0)532 (26.2)
≥8013,077 (34.6)945 (20.3)1,625 (19.6)4,050 (38.7)4,082 (47.1)559 (41.0)856 (42.2)
≥6030,866 (81.7)3,474 (74.5)5,927 (71.4)8,900 (85.1)7,639 (88.1)1,180 (86.5)1,767 (87.1)
Region
Metropolitan area23,347 (61.9)3,402 (72.9)6,184 (74.5)5,975 (57.1)4,960 (57.2)713 (52.2)932 (46.0)
Seoul10,337 (27.4)1,876 (40.2)3,348 (40.3)2,275 (21.7)1,707 (19.7)276 (20.2)412 (20.3)
Gyeonggi10,183 (27.0)1,238 (26.5)2,255 (27.2)2,746 (26.3)2,589 (29.8)359 (26.3)420 (20.7)
Incheon2,827 (7.5)288 (6.2)581 (7.0)954 (9.1)664 (7.7)78 (5.7)100 (5.0)
Non-metropolitan area14,287 (37.8)1,166 (25.0)2,085 (25.2)4,484 (42.9)3,714 (42.8)651 (47.8)1,096 (54.0)
Busan2,347 (6.2)156 (3.3)433 (5.2)723 (6.9)566 (6.5)108 (7.9)189 (9.3)
Deagu1,806 (4.8)240 (5.1)258 (3.1)613 (5.9)412 (4.7)54 (4.0)130 (6.4)
Gwangju811 (2.2)65 (1.4)70 (0.9)301 (2.9)229 (2.6)29 (2.1)47 (2.3)
Daejeon883 (2.3)71 (1.5)168 (2.0)269 (2.6)209 (2.4)36 (2.6)61 (3.0)
Ulsan660 (1.8)75 (1.6)99 (1.2)196 (1.9)177 (2.0)23 (1.7)43 (2.1)
Sejong82 (0.2)2 (0.0)12 (0.2)31 (0.3)23 (0.3)3 (0.2)4 (0.2)
Gangwon1,338 (3.5)99 (2.1)175 (2.1)444 (4.2)361 (4.2)65 (4.8)95 (4.7)
Chungbuk754 (2.0)64 (1.4)138 (1.7)265 (2.5)172 (2.0)32 (2.4)41 (2.0)
Chungnam1,486 (3.9)97 (2.1)226 (2.7)395 (3.8)470 (5.4)61 (4.5)115 (5.7)
Jeonbuk711 (1.9)58 (1.2)81 (1.0)247 (2.4)183 (2.1)33 (2.4)54 (2.7)
Jeonnam758 (2.0)42 (0.9)63 (0.8)239 (2.3)205 (2.4)43 (3.2)88 (4.3)
Gyeongbuk1,020 (2.7)94 (2.0)100 (1.2)274 (2.6)311 (3.6)69 (5.1)77 (3.8)
Gyeongnam1,403 (3.7)88 (1.9)235 (2.8)404 (3.9)370 (4.3)81 (5.9)109 (5.4)
Jeju228 (0.6)15 (0.3)27 (0.3)83 (0.8)26 (0.3)14 (1.0)43 (2.1)
Quarantine126 (0.3)97 (2.1)27 (0.3)1 (0.0)1 (0.0)0 (0.0)0 (0.0)

Unit: n (%). a)Severe/critical case: Patient who were treated with non-invasive ventilation, high flow oxygenation, invasive ventilation, extracorporeal membrane oxygenation, continuous renal replacement treatment during quarantine from coronavirus disease 2019. b)Number of confirmed cases (≥80): Pre-Delta dominant period 187,340 (6,083, 3.2%), Delta dominant period 500,414 (15,600, 3.1%), Omicron BA.1/BA.2 dominant period 17,800,369 (516,128, 2.9%), Omicron BA.5 dominant period 9,912,503 (411,067, 4.1%), Omicron BN.1 dominant period 777,942 (42,126, 5.4%), Omicron XBB dominant period 2,224,486 (112,926, 5.1%)..


Characteristics of coronavirus disease 2019 deaths by period (as of July 31, 2023)
ClassVariants dominant period
Total (2020.1.20.-2023.7.31.)Pre-Delta (2020.1.20.-2021.7.24.)Delta dominant period (2021.7.25.-2022.1.15.)Omicron dominant period
BA.1/BA.2 (2022.1.16.-2022.7.9.)BA.5 (2022.7.24.-2022.12.31.)BN.1 (2023.1.22.-2023.3.25.)XBB (2023.4.16.-2023.7.31.)
Total35,644 (100.0)2,163 (100.0)4,772 (100.0)18,679 (100.0)6,838 (100.0)809 (100.0)984 (100.0)
Sex
Male17,615 (49.4)1,091 (50.4)2,487 (52.1)8,881 (47.5)3,455 (50.5)444 (54.9)527 (53.6)
Female18,029 (50.6)1,072 (49.6)2,285 (47.9)9,798 (52.5)3,383 (49.5)365 (45.1)457 (46.4)
Age (yr)
Average±standard deviation79.2±12.278.4±11.477.2±12.280.4±12.180.2±12.278.8±12.780.4±11.9
0-939 (0.1)0 (0.0)3 (0.1)21 (0.1)10 (0.1)0 (0.0)2 (0.2)
10-1924 (0.1)0 (0.0)0 (0.0)13 (0.1)6 (0.1)3 (0.4)1 (0.1)
20-2981 (0.2)5 (0.2)10 (0.2)48 (0.3)15 (0.2)0 (0.0)1 (0.1)
30-39166 (0.5)11 (0.5)33 (0.7)70 (0.4)33 (0.5)8 (1.0)5 (0.5)
40-49480 (1.3)20 (0.9)79 (1.7)242 (1.3)94 (1.4)12 (1.5)10 (1.0)
50-591,446 (4.1)105 (4.9)233 (4.9)708 (3.8)269 (3.9)38 (4.7)28 (2.8)
60-694,044 (11.3)284 (13.1)822 (17.2)1,897 (10.1)684 (10.0)99 (12.2)103 (10.6)
70-798,065 (22.6)604 (28.0)1,300 (27.2)4,001 (21.4)1,476 (21.6)178 (22.0)206 (20.9)
≥8021,299 (59.8)1,134 (52.4)2,292 (48.0)11,679 (62.5)4,251 (62.2)471 (58.2)628 (63.8)
≥6033,408 (93.7)2,022 (93.5)4,414 (92.4)17,577 (94.0)6,411 (93.8)748 (92.4)937 (95.3)
Region
Metropolitan area17,185 (48.2)1,337 (61.8)3,544 (74.3)8,048 (43.1)2,971 (43.4)299 (37.0)403 (41.0)
Seoul6,638 (18.6)555 (25.7)1,717 (36.0)2,719 (14.6)1,105 (16.1)117 (14.5)193 (19.6)
Gyeonggi8,586 (24.1)714 (33.0)1,541 (32.3)4,244 (22.7)1,526 (22.3)131 (16.2)158 (16.1)
Incheon1,961 (5.5)68 (3.1)286 (6.0)1,085 (5.8)340 (5.0)51 (6.3)52 (5.3)
Non-metropolitan area18,443 (51.7)814 (37.6)1,224 (25.6)10,631 (56.9)3,867 (56.6)510 (63.0)581 (59.0)
Busan2,926 (8.2)130 (6.0)245 (5.1)1,878 (10.1)441 (6.4)44 (5.4)80 (8.1)
Deagu2,061 (5.8)222 (10.3)166 (3.5)1,026 (5.5)453 (6.6)56 (6.9)51 (5.2)
Gwangju858 (2.4)24 (1.1)48 (1.0)536 (2.9)172 (2.5)19 (2.3)19 (1.9)
Daejeon991 (2.8)34 (1.6)157 (3.3)529 (2.8)169 (2.5)32 (4.0)29 (2.9)
Ulsan544 (1.5)40 (1.8)28 (0.6)314 (1.7)116 (1.7)11 (1.4)13 (1.3)
Sejong59 (0.2)1 (0.0)3 (0.1)32 (0.2)12 (0.2)1 (0.1)3 (0.3)
Gangwon1,388 (3.9)56 (2.6)65 (1.4)769 (4.1)346 (5.1)36 (4.5)54 (5.5)
Chungbuk1,087 (3.0)71 (3.3)55 (1.2)629 (3.4)218 (3.2)28 (3.5)34 (3.5)
Chungnam1,635 (4.6)46 (2.1)139 (2.9)896 (4.8)413 (6.0)38 (4.7)40 (4.1)
Jeonbuk1,270 (3.6)60 (2.8)65 (1.4)802 (4.3)223 (3.3)35 (4.3)28 (2.8)
Jeonnam1,071 (3.0)18 (0.8)30 (0.6)548 (2.9)309 (4.5)53 (6.5)61 (6.2)
Gyeongbuk2,161 (6.1)88 (4.1)114 (2.4)1,301 (7.0)463 (6.8)52 (6.4)51 (5.2)
Gyeongnam2,077 (5.8)23 (1.1)97 (2.0)1,196 (6.4)476 (7.0)97 (12.0)85 (8.6)
Jeju315 (0.9)1 (0.0)12 (0.3)175 (0.9)56 (0.8)8 (1.0)33 (3.4)
Quarantine16 (0.0)12 (0.6)4 (0.1)0 (0.0)0 (0.0)0 (0.0)0 (0.0)

Unit: n (%)..


Case severity rate and case fatality rate by variant dominant period (as of July 31, 2023)
ClassVariants dominant period
Total (2020.1.20.-2023.7.31.)Pre-Delta (2020.1.20.-2021.7.24.)Delta dominant period (2021.7.25.-2022.1.15.)Omicron dominant period
BA.1/BA.2 (2022.1.16.-2022.7.9.)BA.5 (2022.7.24.-2022.12.31.)BN.1 (2023.1.22.-2023.3.25.)XBB (2023.4.16.-2023.7.31.)
Case severity rate (yr)a)0.192.982.140.150.140.250.12
0-90.010.000.02<0.010.010.030.03
10-19<0.010.020.04<0.01<0.010.01<0.01
20-290.010.150.190.010.010.01<0.01
30-390.020.450.560.010.010.020.01
40-490.041.040.980.020.020.040.02
50-590.102.261.910.060.050.110.05
60-690.275.313.590.190.140.300.15
70-790.7513.638.880.700.470.870.34
≥802.4225.4219.752.731.742.131.18
Case fatality rate (yr)b)0.101.150.950.100.070.100.04
0-9<0.010.000.01<0.01<0.010.00<0.01
10-19<0.010.000.00<0.01<0.01<0.01<0.01
20-29<0.010.020.01<0.01<0.010.00<0.01
30-39<0.010.040.04<0.01<0.010.01<0.01
40-490.010.070.110.010.010.01<0.01
50-590.030.310.360.030.020.040.01
60-690.111.141.170.110.060.100.03
70-790.405.594.420.470.220.300.11
≥801.7418.6414.692.261.031.120.56
Mortality rate (per 1,000,000) (yr)69.294.209.2836.3113.291.571.91
0-91.100.000.080.590.280.000.06
10-190.510.000.000.280.130.060.02
20-291.260.080.160.750.230.000.02
30-392.510.170.501.060.500.120.08
40-495.950.250.983.001.160.150.12
50-5916.791.222.718.223.120.440.33
60-6954.623.8411.1025.629.241.341.39
70-79210.8115.7933.98104.5838.584.655.38
≥80944.0750.26101.59517.67188.4220.8827.84

Unit: %. a)Case severity rate: (number of severe/critical cases and deaths among confirmed cases in specific period)/number of confirmed cases in specific period×100. b)Case fatality rate: (number of deaths among confirmed cases in specific period)/number of confirmed cases in specific period×100..


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