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Public Health Weekly Report 2022; 15(47): 2873-2895

Published online November 24, 2022

https://doi.org/10.56786/PHWR.2022.15.47.2873

© The Korea Disease Control and Prevention Agency

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

Boyeong Ryu, Eunjeong Shin, Na-Young Kim, Dong Hwi Kim, HyunJu Lee, Ahra Kim, Shin Young Park, Seonhee Ahn, Jinhwa Jang, Seong-Sun Kim, Donghyok Kwon*

Data Analysis Team, Epidemiological Investigation and Analysis Task Force, Central Disease Control Headquarters, Korea Disease Control and Prevention Agency (KDCA), Cheongju, Korea

*Corresponding author: Donghyok Kwon, Tel: +82-43-719-7730, E-mail: vethyok@korea.kr

Received: October 12, 2022; Revised: October 19, 2022; Accepted: October 19, 2022

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.

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 , 2 022. 2 6,472 (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.

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

Key messages

① What is known previously?

As the COVID-19 pandemic continues, changes in the immunity of population due to SARS-CoV-2 variants, vaccination, and re-infection have been affecting the severity of COVID-19 infection.

② What new information is presented?

Despite the high severity of delta variant, the severity of COVID-19 have been decreased in whole period. However, in the omicron dominant period, the proportion of the age 80 and over among severe/critical cases and deaths increased with 26.4%p, 7.4%p, respectively than those in the delta dominant period.

③ What are implications?

As the proportion of severe/critical and deaths cases of the elderly has increased, it is important to focus on the response strategy to the elderly.

Coronaviruses that infect humans can cause common colds, such as HCoV-229E and HCoV-NL63. They can also cause severe respiratory diseases, such as severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome–related coronavirus [1]. The Coronavirus disease 2019 (COVID-19) first reported in China in late 2019 was a new, previously unidentified strain of coronavirus, and its severity was then unknown [2]. In addition, COVID-19 has continued to spread worldwide, resulting in variants of SARS-CoV-2. At the same time, the characteristics of the virus, such as transmissibility and severity, have gradually changed. The Alpha variant, which was first reported in the United Kingdom (UK) in late 2020, caused large number of confirmed cases in the UK that winter, and studies have demonstrated that it has increased transmissibility [3]. The Alpha variant was first reported in the Republic of Korea (ROK) in December 2020 and has since spread throughout various communities, but the detection rate in variant testing among confirmed cases in the ROK was no more than 50% [4]. Among the significant variants designated by the World Health Organization (WHO), the Beta and Gamma variants also reported in the ROK. Similarly, the detection rate was not more than 50% [4]. However, not only did the Delta and Omicron variants cause large-scale community outbreaks after their introduction in the ROK, but outbreaks have been reported in more than 200 countries worldwide [5]. The characteristics of these viruses were distinctly different from the preexisting viruses, ushering in a new phase of the COVID-19 pandemic [6]. Both variants have been reported to have increased transmissibility, though the severity has increased for the Delta variant and decreased for the Omicron variant [7-9].

Meanwhile, through the rapid development of COVID-19 vaccines, the world has largely been vaccinated against COVID-19 since the end of 2020; this has played a significant role in preventing not only COVID-19 infection but also the progression to severe diseases. Studies on the preventive effects of COVID-19 vaccination found that the preventive effect of infection during COVID-19 vaccination periods decreased from 83% one month after vaccination to 22% five months after vaccination. In particular, the appearance of variants characterized by immune evasion reduced the preventive effects through vaccination [10-12]. However, the preventive effects of vaccination against severe infections that can lead to severe or critical conditions or death during COVID-19 infection have remained high over time [10]. In the ROK, COVID-19 vaccination began for elderly in February 2021, and, as of October 4, 2022, 87.1% of the population has received the second dose and 65.5%, the third or more doses [13].

The domestic and global public health response to the COVID-19 pandemic, which has been going on for more than 2 years, is shifting from strong control policies for defeating the disease to mitigation policies for living with COVID-19 [14-16]. As the COVID-19 response strategy has been changed to minimize impacts from COVID-19, the size of the severe cases and severity including severe, critical cases and death related COVID-19 have been used as essential indicators for establishing response strategies. Therefore, this report aimed to identify the severe/critical cases and deaths related to COVID-19 that had changed due to the continuous emergence of new variants and the implementation of COVID-19 vaccination over the last 2 years and 7 months since the first case of COVID-19 occurred in January 2020. We calculate the case severity rate and case fatality rate to determine the priority and scope of COVID-19 response policies and to use the results of this study as evidence for preparing relevant health care resources.

1. Study Population

Among the COVID-19 confirmed cases reported from January 20, 2020, when the first COVID-19 case was reported in the ROK, to September 3, 2022, those who progressed to severe or critical conditions or death were monitored. The pandemic periods were classified according to the predominant variants of COVID-19 to identify the scale and demographic characteristics of the outbreak. A confirmed COVID-19 case was defined as a person whose infection was confirmed through RT-PCR or virus isolation following the COVID-19 response guidelines or a person with symptoms of COVID-19 who were diagnosed by a doctor after a positive rapid antigen test (for professionals) or emergency screening test. The severity was classified as “severe or critical condition” and “death.” The severity rate included both “severe or critical condition” and “death.” The fatality rate included only death. The severity rate was calculated together with death cases due to the possibility of an underestimation of severity, as some patients with severe conditions from long-term care facilities died without experiencing critical conditions and can be excluded from the monitoring of severe cases. The severe or critical conditions were defined as patients isolated at a medical institution after being diagnosed with COVID-19. They received non-invasive or invasive ventilation, high-flow oxygen therapy, extracorporeal membrane oxygenation, or continuous renal replacement therapy following the Korean COVID-19 response guideline based on ‘the Ordinal scale for clinical improvement’ suggested by the WHO at the beginning of the COVID-19 pandemic [17,18]. The clinical status of confirmed cases was monitored based on data and telephone communication reported by public health centers and medical institutions through the COVID-19 Patient Management Information System (Central Diseases Control Headquarters) and the Health and Medical Resources Integrated Reporting Portal System (Central Disaster Management Investigation Headquarters). The deaths were counted as COVID-19-related deaths after excluding deaths from foreign causes. This was done by investigating those reported as deaths of confirmed COVID-19 cases following the Infectious Disease Control and Prevention Act. Considering the progression to be “severe or critical” and “death” after COVID-19 diagnosis, the clinical progress of confirmed cases was monitored until September 17, 2022.

2. Data Analysis

The epidemic periods were divided based on the week in which more than 50% tested positive for weekly variant tests according to the reporting date of the SARS-CoV-2 variant analysis. The epidemic was divided into the following periods: before the Delta variant was dominant (January 1, 2020 to July 24, 2021), when the Delta variant was dominant (July 25, 2021 to January 15, 2022), and when the Omicron variant was dominant (January 16, 2022 to September 3, 2022). In detail, the Omicron variant dominant period was divided into the BA.1 and BA.2 dominant period (January 16, 2022 to July 23, 2022) and BA.5 dominant period (July 24, 2022 to September 3, 2022) based on BA.5. Vaccination history was classified based on the final vaccination history 14 days before the COVID-19 diagnosis. In the case of Janssen, this was considered as receiving the second dose after receiving the first dose. To understand the scale and characteristics of the occurrence of severe and critical patients and deaths, demographic characteristics, including sex and age, vaccination rate, and incidence status by reported region according to the epidemic periods, were calculated based on the date of diagnosis confirmation. In addition, to understand the severity of COVID-19 according to the epidemic periods, the severity was divided into two levels to calculate the case severity rate (CSR) and case fatality rate (CFR) of each epidemic period and week. CSR was calculated as the proportion (%) of severe or critical patients among confirmed patients during the relevant periods (epidemic periods and weeks). CFR was calculated as the proportion (%) of deaths among confirmed patients during the relevant periods (epidemic periods and weeks). In addition, to understand the scale of deaths relative to the total population, mortality rates by periods were calculated on a weekly average and per million people for the proportion of deaths in the total population. To compare the severity by age, the age group was divided into 10-year-old units to calculate the severity, fatality, and mortality rates. We used the Excel 2016 program (Microsoft, Redmond, WA, USA) for all of the analyses.

From COVID-19 first reported to now, September 3, 2022, 23,496,820 confirmed cases were reported in the ROK, of which 26,472 (0.11%) were in severe or critical conditions and 27,471 (0.12%) died. Among the patients who were recognized as having severe or critical conditions after being diagnosed with COVID-19, 7,507 died, and 46,436 (0.20%) progressed to severe or critical conditions or death in total.

1. Status of Patients with Severe or Critical Conditions

Of the 26,472 patients with severe or critical conditions confirmed during the COVID-19 outbreak, the highest number of patients with severe or critical conditions, which accounted for 40.7% (10,772) of all patients with severe or critical conditions, occurred during the Omicron BA.1/BA.2 dominant period (Table 1). Additionally, this period accounted for 78.6% of the total confirmed cases. Compared to the Delta variant dominant periods, the number of confirmed cases increased sharply (34.1 times) and the number of patients with severe or critical conditions increased (1.3 times) during the Omicron BA.1/BA.2 dominant period (Figure 1). However, due to the decrease in the severity of the Omicron variant, the increase in the number of patients with severe or critical conditions was low compared to the increase in confirmed cases. Males accounted for more than 56% of the total period, which was 13% more than females. The average age of the patients with severe or critical conditions gradually increased from 67.7 years (±13.7 years) before the Delta variant dominance to 74.6 years (±15.7 years) during the Omicron BA.5 dominant period. The proportion of patients over 80 years of age increased by 26.3%, from 20.3% prior to the dominance of the Delta variant to 46.6% during the Omicron BA.5 dominant period. Before the Delta variant dominant period, 97.3% were unvaccinated, whereas 73.1% were vaccinated with at least one dose during the Omicron variant dominant period due to the improving vaccination rate. The metropolitan area, including Seoul, Gyeonggi, and Incheon, accounted for 72.9% before the Delta variant dominance. However, as the proportion of confirmed cases in non-metropolitan areas increased during the Omicron variant dominant period, that of patients with severe or critical conditions increased from 25.0% before the Delta variant dominant period to 44.5%.

Figure 1. Weekly number of confirmed cases, severe/critical cases and deaths (as of September 3, 2022)

Table 1.

Characteristics of COVID-19a) severe/critical casesb) by period (as of September 3, 2022)

ClassTotalPre-Delta dominant periodDelta dominant periodOmicron dominant period
BA.1/BA.2BA.5
Total26,472(100.0)4,665(100.0)8,296(100.0)10,772(100.0)2,739(100.0)
Sex
Male15,303(57.8)2,792(59.8)4,775(57.6)6,184(57.4)1,552(56.7)
Female11,169(42.2)1,873(40.2)3,521(42.4)4,588(42.6)1,187(43.3)
Age
Average (±SD)69.9±15.767.7±13.766.0±15.472.7±15.874.6±15.7
0–9 yr103(0.4)0(0.0)6(0.1)77(0.7)20(0.7)
10–19 yr107(0.4)3(0.1)21(0.3)68(0.6)15(0.5)
20–29 yr303(1.1)44(0.9)129(1.6)108(1.0)22(0.8)
30–39 yr768(2.9)116(2.5)399(4.8)199(1.8)54(2.0)
40–49 yr1,398(5.3)298(6.4)664(8.0)356(3.3)80(2.9)
50–59 yr2,837(10.7)730(15.6)1,150(13.9)800(7.4)157(5.7)
60–69 yr5,966(22.5)1,240(26.6)2,217(26.7)2,090(19.4)419(15.3)
70–79 yr6,948(26.2)1,289(27.6)2,084(25.1)2,880(26.7)695(25.4)
≥80 yr8,042(30.4)945(20.3)1,626(19.6)4,194(38.9)1,277(46.6)
≥60 yrc)20,956(79.2)3,474(74.5)5,927(71.4)9,164(85.1)2,391(87.3)
Vaccination
None14,627(55.3)4,539(97.3)5,031(60.6)4,321(40.1)736(26.9)
1 dose1,100(4.2)118(2.5)580(7.0)347(3.2)55(2.0)
2 dose4,552(17.2)8(0.2)2,595(31.3)1,656(15.4)293(10.7)
≥3 dose6,193(23.4)0(0.0)90(1.1)4,448(41.3)1,655(60.4)
Region
Metropolitan area17,279(65.3)3,402(72.9)6,184(74.5)6,172(57.3)1,521(55.5)
Seoul8,118(30.7)1,876(40.2)3,348(40.4)2,348(21.8)546(19.9)
Gyeonggi7,115(26.9)1,238(26.5)2,255(27.2)2,845(26.4)777(28.4)
Incheon2,046(7.7)288(6.2)581(7.0)979(9.1)198(7.2)
Non-metropolitan area9,068(34.3)1,166(25.0)2,085(25.1)4,599(42.7)1,218(44.5)
Busan1,493(5.6)156(3.3)433(5.2)738(6.9)166(6.1)
Daegu1,266(4.8)240(5.1)258(3.1)626(5.8)142(5.2)
Gwangju532(2.0)65(1.4)70(0.8)305(2.8)92(3.4)
Daejeon591(2.2)71(1.5)168(2.0)275(2.6)77(2.8)
Ulsan440(1.7)75(1.6)99(1.2)200(1.9)66(2.4)
Sejong55(0.2)2(0.0)12(0.1)32(0.3)9(0.3)
Gangwon837(3.2)99(2.1)175(2.1)455(4.2)108(3.9)
Chungbuk532(2.0)64(1.4)138(1.7)268(2.5)62(2.3)
Chungnam903(3.4)97(2.1)226(2.7)411(3.8)169(6.2)
Jeonbuk464(1.8)58(1.2)81(1.0)257(2.4)68(2.5)
Jeonnam425(1.6)42(0.9)63(0.8)248(2.3)72(2.6)
Gyeongbuk541(2.0)94(2.0)100(1.2)277(2.6)70(2.6)
Gyeongnam850(3.2)88(1.9)235(2.8)419(3.9)108(3.9)
Jeju139(0.5)15(0.3)27(0.3)88(0.8)9(0.3)
Quarantine125(0.5)97(2.1)27(0.3)1(0.0)0(0.0)

Values are presented as number (%). SD=standard deviation. a)Severe/critical case: Patient who were treated with non-invasive ventilation, high flow oxygenation, invasive ventilation, Extracorporeal membrane oxygenation (ECMO), Continuous renal replacement treatment (CRRT) during quarantine from COVID-19. b)Number of confirmed cases (≥80): Pre-Delta dominant period 187,349 (6,085, 3.2%), Delta dominant period 500,572 (15,602, 3.1%), Omicron BA.1/BA.2 dominant period 18,457,796 (528,350, 2.9%), Omicron BA.5 dominant period 4,351,103 (153,356, 3.5%). c)Over 60s.



2. Deaths

Of the 27,471 deaths during the COVID-19 pandemic, 66.4% (18,252) occurred during the Omicron BA.1/BA.2 dominant period. The number of deaths increased (3.6 times) due to the surge in confirmed cases (34.1 times) during the Omicron BA.1/BA.2 dominant period. Still, the increase in the number of deaths was lower than that of confirmed cases due to the decrease in the severity of the Omicron variant (Table 2, Figure 1). Differences in sex across the periods were similarly within 5% for each variant dominance period. The average age was also similar, being in the range of 77.2–80.2 years. Still, by age group, the proportion of people over 80 years old increased from 52.5% (1,135 people) before the dominance of the Delta variant to 62.3% (11,379 people) during the dominance of Omicron BA.1/BA.2 and 59.9% (1,378 people) during the dominance of Omicron BA.5. The unvaccinated rate before the dominance of the Delta variant was 98.8%. However, during the dominant period of the Omicron variant, the unvaccinated rate was 29.0% due to the increase in vaccination rate. Before the dominance of the Delta variant, 61.7% of deaths occurred in the metropolitan area. During the dominance of the Delta variant, 74.3% of deaths occurred in the metropolitan area, with an increase in confirmed cases in metropolitan areas. Additionally, during the Omicron variant dominant period, 58.3% of the total deaths occurred in non-metropolitan areas due to the increase in confirmed cases in these areas, which was more than in the metropolitan areas.

Table 2.

Characteristics of COVID-19 deaths by period (as of September 3, 2022)

ClassTotalPre-Delta dominant periodDelta dominant periodOmicron dominant period
BA.1/BA.2BA.5
Total27,471(100.0)2,162(100.0)4,758(100.0)18,252(100.0)2,299(100.0)
Sex
Male13,437(48.9)1,091(50.5)2,478(52.1)8,677(47.5)1,191(51.8)
Female14,034(51.1)1,071(49.5)2,280(47.9)9,575(52.5)1,108(48.2)
Age
Average (±SD)79.5±12.278.4±11.477.2±12.280.2±12.279.5±12.6
0–9 yr31(0.1)0(0.0)3(0.1)24(0.1)4(0.2)
10–19 yr16(0.1)0(0.0)0(0.0)14(0.1)2(0.1)
20–29 yr68(0.2)5(0.2)10(0.2)47(0.3)6(0.3)
30–39 yr130(0.5)11(0.5)33(0.7)70(0.4)16(0.7)
40–49 yr376(1.4)20(0.9)78(1.6)242(1.3)36(1.6)
50–59 yr1,143(4.2)105(4.9)232(4.9)705(3.9)101(4.4)
60–69 yr3,200(11.6)284(13.1)816(17.2)1,874(10.3)226(9.8)
70–79 yr6,326(23.0)602(27.8)1,297(27.3)3,897(21.4)530(23.1)
≥80 yr16,181(58.9)1,135(52.5)2,289(48.1)11,379(62.3)1,378(59.9)
≥60 yra)25,707(93.6)2,021(93.5)4,402(92.5)17,150(94.0)2,134(92.8)
Vaccination
None12,429(45.2)2,137(98.8)2,645(55.6)6,981(38.2)666(29.0)
1 dose1,053(3.8)22(1.0)260(5.5)721(4.0)50(2.2)
2 dose4,946(18.0)3(0.1)1,786(37.5)2,919(16.0)238(10.4)
≥3 dose9,043(32.9)0(0.0)67(1.4)7,631(41.8)1,345(58.5)
Region
Metropolitan area13,780(50.2)1,335(61.7)3,537(74.3)7,950(43.6)958(41.7)
Seoul5,344(19.5)554(25.6)1,714(36.0)2,708(14.8)368(16.0)
Gyeonggi6,940(25.3)713(33.0)1,539(32.3)4,169(22.8)519(22.6)
Incheon1,496(5.4)68(3.1)284(6.0)1,073(5.9)71(3.1)
Non-metropolitan area13,675(49.8)815(37.7)1,217(25.6)10,302(56.4)1,341(58.3)
Busan2,403(8.7)130(6.0)244(5.1)1,872(10.3)157(6.8)
Daegu1,569(5.7)222(10.3)166(3.5)1,015(5.6)166(7.2)
Gwangju634(2.3)24(1.1)48(1.0)502(2.8)60(2.6)
Daejeon773(2.8)34(1.6)157(3.3)531(2.9)51(2.2)
Ulsan396(1.4)41(1.9)25(0.5)284(1.6)46(2.0)
Sejong43(0.2)1(0.0)3(0.1)34(0.2)5(0.2)
Gangwon1,007(3.7)56(2.6)65(1.4)763(4.2)123(5.4)
Chungbuk827(3.0)71(3.3)54(1.1)619(3.4)83(3.6)
Chungnam1,156(4.2)46(2.1)139(2.9)820(4.5)151(6.6)
Jeonbuk962(3.5)60(2.8)64(1.3)773(4.2)65(2.8)
Jeonnam645(2.3)18(0.8)29(0.6)473(2.6)125(5.4)
Gyeongbuk1,598(5.8)88(4.1)114(2.4)1,267(6.9)129(5.6)
Gyeongnam1,448(5.3)23(1.1)97(2.0)1,173(6.4)155(6.7)
Jeju214(0.8)1(0.0)12(0.3)176(1.0)25(1.1)
Quarantine16(0.1)12(0.6)4(0.1)0(0.0)0(0.0)

Values are presented as number (%). SD=standard deviation. a)Over 60s.



3. Trends in Case Severity and Fatality Rates

The case severity rates and case fatality rates during the pandemic was 0.20%, and the case fatality rate was 0.12%. These rates were the highest at 2.98% and 1.15%, respectively, before the Delta variant dominant period and lowest at 0.10% and 0.05%, respectively, during the Omicron BA.5 dominant period (Table 3, Figure 2). The case severity rate decreased from 2.98% before the dominance of the Delta variant to 2.14% during the Delta variant dominant period. It decreased further to 0.14% during the Omicron BA.1/BA.2 dominant period, which was one-fifteenth the rate during the Delta variant dominant period. It decreased to 0.10% during the Omicron BA.5 dominant period (Figure 2). The case fatality rate also decreased from 1.15% before the Delta variant dominant period to 0.95% during the Delta variant dominant period and 0.10% during the dominance of Omicron BA.1/BA.2, which was one-tenth the rate as when the Delta variant was dominant. During the Omicron BA.5 dominant period, the case fatality rate decreased to 0.05%, half of that during the Omicron BA.1/BA.2 dominant period.

Figure 2. Weekly case severity rate and case fatality rate (as of September 3, 2022)

Table 3.

Case severity rate and case fatality rate by variant dominant period (as of September 3, 2022)

ClassTotal
(Jan 20, 2020–
Sep 3, 2022)
Pre-Delta dominant period
(Jan 20, 2020–
Jul 24, 2021)
Delta dominant period
(Jul 24, 2021–
Jan 15, 2022)
Omicron dominant period
BA.1/BA.2
(Jan 15, 2022–
Jul 23, 2022)
BA.5
(Jul 24, 2022–
Sep 3, 2022)
Case severity ratea)0.202.982.140.140.10
0–9 yr<0.010.000.02<0.010.01
10–19 yr<0.010.020.04<0.01<0.01
20–29 yr0.010.150.190.01<0.01
30–39 yr0.020.450.560.010.01
40–49 yr0.051.040.970.020.02
50–59 yr0.122.261.910.060.04
60–69 yr0.325.313.580.190.11
70–79 yr0.9213.638.870.670.38
≥80 yr2.9725.4219.742.631.51
Case fatality ratea)0.121.150.950.100.05
0–9 yr<0.010.000.01<0.01<0.01
10–19 yr<0.010.000.00<0.01<0.01
20–29 yr<0.010.020.01<0.01<0.01
30–39 yr<0.010.040.04<0.01<0.01
40–49 yr0.010.070.110.010.01
50–59 yr0.040.310.360.030.02
60–69 yr0.131.141.160.100.04
70–79 yr0.535.574.400.450.19
≥80 yr2.3018.6514.672.150.90
Mortality rate (Weekly average, per 1,000.000)6.750.533.6913.097.42
0–9 yr0.100.000.030.240.18
10–19 yr0.040.000.000.110.07
20–29 yr0.130.010.060.260.15
30–39 yr0.250.020.200.390.40
40–49 yr0.580.030.381.100.73
50–59 yr1.680.151.073.021.95
60–69 yr5.660.504.569.695.26
70–79 yr21.592.0513.9638.8523.78
≥80 yr97.346.8343.43199.93108.95

Values are presented as %. 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 severity, fatality, and mortality rates by periods and age groups all increased with age, and there were differences in the level of severity change according to epidemic periods for each age group. During the transition from before the dominance of the Delta variant to the dominance of the Delta variant, the case severity rate increased among those in their 30s or younger and decreased among those in their 40s. The case fatality rate increased among those in their 60s or younger and decreased among those in their 70s. During the transition from the dominance of the Delta variant to that of the Omicron variant, severity and case fatality rates in all age groups decreased, with the largest relative decline among those in their 30s (0.56% → 0.01%, 1/61 times) and the smallest decline among those in their 80s (19.74% → 2.63%, 1/8 times) among adults over 20 years of age. The absolute risk decreased the most in the age group over 80 years at 17.11%. Regarding the case fatality rate, the relative risk also decreased the most among those in their 30s (0.045% → 0.003%, 1/17 times) and decreased the least among those in their 80s (14.67 → 2.15%, 1/7 times). The largest absoulte reduction in case fatality rate was among those over 80 years of age, with a decrease of 12.52%. During the Omicron BA.1/BA.2 dominant period, the severity and case fatality rates were less than 1% in all age groups except those 80 years of age and older. During the Omicron BA.5 dominant period, the case severity rate was less than 1% in all age groups except those 80 years of age and older, and the case fatality rate was less than 1% in all age groups.

The mortality rate was the highest at an average of 13 per million per week due to the explosive increase in confirmed cases during the Omicron BA.1/BA.2 dominant period. The absolute risk also increased sharply with age, with a weekly average of 200 death per million people during the Omicron BA.1/BA.2 dominant period for those over 80 years of age and 109 deaths per million during the Omicron BA.5 dominant period.

This report analyzed the trend of the severity of COVID-19 from the date of the first confirmed case of COVID-19 in the ROK to the latest at the time of writing (September 3, 2022). We categorized the patients by severity (severe or critical conditions and death), period, and demographic through monitoring the clinical status of COVID-19 cases. In the period before the dominance of the Delta variant, the case severity rate was 2.98%; it was up to 6.95% in its weekly rate. The increase and decrease were repeated in the first year of the COVID-19 outbreak but gradually remained constant from 2021. The Delta variant has been reported to be more transmissible and severe than the preexisting viruses [7]. Whereas, in the ROK, the severity of all age groups during the Delta variant dominant period decreased to 2.14%. When divided by age group, there were differences in the increase or decrease in severity. The case severity rate increased among those in their 30s or younger, and the case fatality rate increased among those in their 60s or younger.

On the other hand, during the period of dominance of the Omicron variant, a sharp decrease in severity in all age groups was found, which was consistent with a global decrease in the severity of the Omicron variant [8,9]. However, the Omicron variant is more transmissible than preexisting variants and acts via immune evasion. Thus, the number of confirmed cases increased sharply by more than 30 times on average per day during the Omicron BA.1/BA.2 dominant period compared to the Delta variant dominant period, leading to the increase in the number of patients with severe or critical conditions and deaths. However, due to the decrease in severity, this increase rate was lower than the increase rate of confirmed cases, with a 1.3-fold increase in severe or critical cases and a 3.8-fold increase in deaths. The absolute reduction in severity during the Omicron BA.1/BA.2 dominant period compared to the Delta variant dominant period in the adult age groups over 20 years old was greatest in the group over 80 years of age, though the relatively smallest decrease was among those over 80 years of age compared to other age groups. This suggests that severe or critical cases and deaths are mostly in elderly over 80 years of age, when the severity has decreased due to the Omicron variant, indicating that appropriate measures for elderly are more important than before.

While responding to COVID-19 in the ROK, the results of monitoring COVID-19 severity were used as evidence for establishing response strategy strategies by periods. In early 2020, the severity of the outbreak was unknown; therefore, all confirmed patients were hospitalized in isolation. Through monitoring the severity of the confirmed cases, asymptomatic and mild confirmed cases were separated and managed in Residential Treatment Centers and as inpatients, which distributed health and medical resources for treating severe cases on time. With the announcement of the roadmap for gradual return to normal in October 2021, the COVID-19 response strategy focused on curbing the occurrence of severe cases caused by COVID-19 infection. Accordingly, the number of new severe or critical cases was a key indicator in the risk assessment of COVID-19. In addition, the results of monitoring severe or critical cases and deaths are used as primary data for the evaluation of vaccine effectiveness and the severity of a new variant of SARS-CoV-2.

The limitations of this report were as follows. First, the COVID-19 Severe Patient Surveillance System collects clinical information and registration reported by public health centers and medical institutions. Thus, cases in which clinical information is not reported in a timely manner or deaths are not captured, which may cause an underestimation. Second, since the data was classified based on the vaccination history entered into the immunization system, it was impossible to adjust the cases in which vaccination history was incorrectly entered. Third, this report was a result of analyzing only crude rates and did not adjust for differences in the demographic characteristics of confirmed cases, such as age and periods. However, it was possible to identify trends in the severity of confirmed cases with multiple characteristics for the purpose of viewing the severity of entire communities.

The severity of COVID-19 has decreased as the Omicron variant has become dominant, but as there is a large proportion of elderly among severe cases, the management of this population is becoming more important. In addition, the impact of the COVID-19 epidemic on various communities continues to change due to the emergence of new variants, the increase in vaccination, the decrease in the prevention effect over time after vaccination, the increase in reinfection due to immune evasion despite the patient’s previous infection history, and the increase in the number of unconfirmed infections in various communities. As such, it is necessary to closely monitor the severity of COVID-19 in these communities and to establish response strategies accordingly.

Ethics Statement: Not applicable.

Funding Source: None.

Acknowledgments: We would like to thank National Medical Center for monitoring severe and critical patients of COVID-19, and Regional centers for Disease Control and Prevention for investigation of COVID-19 deaths.

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

Author Contributions: Conceptualization: BYR. Data curation: BYR. Formal analysis: BYR. Investigation: BYR, EJS, NYK, DHK, HJL. Methodology: BYR, SSK. Project administration: SSK. Resources: BYR, EJS, NYK, DHK, HJL, ARK. SYP, JHJ. Software: BYR. Supervision: DHK. Validation: SSK, DHK. Visualization: BYR. Writing – original draft: BYR. Writing – review & editing: SSK, DHK.

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Surveillance Reports

Public Health Weekly Report 2022; 15(47): 2873-2895

Published online November 24, 2022 https://doi.org/10.56786/PHWR.2022.15.47.2873

Copyright © The Korea Disease Control and Prevention Agency.

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

Boyeong Ryu, Eunjeong Shin, Na-Young Kim, Dong Hwi Kim, HyunJu Lee, Ahra Kim, Shin Young Park, Seonhee Ahn, Jinhwa Jang, Seong-Sun Kim, Donghyok Kwon*

Data Analysis Team, Epidemiological Investigation and Analysis Task Force, Central Disease Control Headquarters, Korea Disease Control and Prevention Agency (KDCA), Cheongju, Korea

Correspondence to:*Corresponding author: Donghyok Kwon, Tel: +82-43-719-7730, E-mail: vethyok@korea.kr

Received: October 12, 2022; Revised: October 19, 2022; Accepted: October 19, 2022

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

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 , 2 022. 2 6,472 (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.

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

Body

Key messages

① What is known previously?

As the COVID-19 pandemic continues, changes in the immunity of population due to SARS-CoV-2 variants, vaccination, and re-infection have been affecting the severity of COVID-19 infection.

② What new information is presented?

Despite the high severity of delta variant, the severity of COVID-19 have been decreased in whole period. However, in the omicron dominant period, the proportion of the age 80 and over among severe/critical cases and deaths increased with 26.4%p, 7.4%p, respectively than those in the delta dominant period.

③ What are implications?

As the proportion of severe/critical and deaths cases of the elderly has increased, it is important to focus on the response strategy to the elderly.

Introduction

Coronaviruses that infect humans can cause common colds, such as HCoV-229E and HCoV-NL63. They can also cause severe respiratory diseases, such as severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome–related coronavirus [1]. The Coronavirus disease 2019 (COVID-19) first reported in China in late 2019 was a new, previously unidentified strain of coronavirus, and its severity was then unknown [2]. In addition, COVID-19 has continued to spread worldwide, resulting in variants of SARS-CoV-2. At the same time, the characteristics of the virus, such as transmissibility and severity, have gradually changed. The Alpha variant, which was first reported in the United Kingdom (UK) in late 2020, caused large number of confirmed cases in the UK that winter, and studies have demonstrated that it has increased transmissibility [3]. The Alpha variant was first reported in the Republic of Korea (ROK) in December 2020 and has since spread throughout various communities, but the detection rate in variant testing among confirmed cases in the ROK was no more than 50% [4]. Among the significant variants designated by the World Health Organization (WHO), the Beta and Gamma variants also reported in the ROK. Similarly, the detection rate was not more than 50% [4]. However, not only did the Delta and Omicron variants cause large-scale community outbreaks after their introduction in the ROK, but outbreaks have been reported in more than 200 countries worldwide [5]. The characteristics of these viruses were distinctly different from the preexisting viruses, ushering in a new phase of the COVID-19 pandemic [6]. Both variants have been reported to have increased transmissibility, though the severity has increased for the Delta variant and decreased for the Omicron variant [7,-9].

Meanwhile, through the rapid development of COVID-19 vaccines, the world has largely been vaccinated against COVID-19 since the end of 2020; this has played a significant role in preventing not only COVID-19 infection but also the progression to severe diseases. Studies on the preventive effects of COVID-19 vaccination found that the preventive effect of infection during COVID-19 vaccination periods decreased from 83% one month after vaccination to 22% five months after vaccination. In particular, the appearance of variants characterized by immune evasion reduced the preventive effects through vaccination [10,-12]. However, the preventive effects of vaccination against severe infections that can lead to severe or critical conditions or death during COVID-19 infection have remained high over time [10]. In the ROK, COVID-19 vaccination began for elderly in February 2021, and, as of October 4, 2022, 87.1% of the population has received the second dose and 65.5%, the third or more doses [13].

The domestic and global public health response to the COVID-19 pandemic, which has been going on for more than 2 years, is shifting from strong control policies for defeating the disease to mitigation policies for living with COVID-19 [14,-16]. As the COVID-19 response strategy has been changed to minimize impacts from COVID-19, the size of the severe cases and severity including severe, critical cases and death related COVID-19 have been used as essential indicators for establishing response strategies. Therefore, this report aimed to identify the severe/critical cases and deaths related to COVID-19 that had changed due to the continuous emergence of new variants and the implementation of COVID-19 vaccination over the last 2 years and 7 months since the first case of COVID-19 occurred in January 2020. We calculate the case severity rate and case fatality rate to determine the priority and scope of COVID-19 response policies and to use the results of this study as evidence for preparing relevant health care resources.

Methods

1. Study Population

Among the COVID-19 confirmed cases reported from January 20, 2020, when the first COVID-19 case was reported in the ROK, to September 3, 2022, those who progressed to severe or critical conditions or death were monitored. The pandemic periods were classified according to the predominant variants of COVID-19 to identify the scale and demographic characteristics of the outbreak. A confirmed COVID-19 case was defined as a person whose infection was confirmed through RT-PCR or virus isolation following the COVID-19 response guidelines or a person with symptoms of COVID-19 who were diagnosed by a doctor after a positive rapid antigen test (for professionals) or emergency screening test. The severity was classified as “severe or critical condition” and “death.” The severity rate included both “severe or critical condition” and “death.” The fatality rate included only death. The severity rate was calculated together with death cases due to the possibility of an underestimation of severity, as some patients with severe conditions from long-term care facilities died without experiencing critical conditions and can be excluded from the monitoring of severe cases. The severe or critical conditions were defined as patients isolated at a medical institution after being diagnosed with COVID-19. They received non-invasive or invasive ventilation, high-flow oxygen therapy, extracorporeal membrane oxygenation, or continuous renal replacement therapy following the Korean COVID-19 response guideline based on ‘the Ordinal scale for clinical improvement’ suggested by the WHO at the beginning of the COVID-19 pandemic [17,18]. The clinical status of confirmed cases was monitored based on data and telephone communication reported by public health centers and medical institutions through the COVID-19 Patient Management Information System (Central Diseases Control Headquarters) and the Health and Medical Resources Integrated Reporting Portal System (Central Disaster Management Investigation Headquarters). The deaths were counted as COVID-19-related deaths after excluding deaths from foreign causes. This was done by investigating those reported as deaths of confirmed COVID-19 cases following the Infectious Disease Control and Prevention Act. Considering the progression to be “severe or critical” and “death” after COVID-19 diagnosis, the clinical progress of confirmed cases was monitored until September 17, 2022.

2. Data Analysis

The epidemic periods were divided based on the week in which more than 50% tested positive for weekly variant tests according to the reporting date of the SARS-CoV-2 variant analysis. The epidemic was divided into the following periods: before the Delta variant was dominant (January 1, 2020 to July 24, 2021), when the Delta variant was dominant (July 25, 2021 to January 15, 2022), and when the Omicron variant was dominant (January 16, 2022 to September 3, 2022). In detail, the Omicron variant dominant period was divided into the BA.1 and BA.2 dominant period (January 16, 2022 to July 23, 2022) and BA.5 dominant period (July 24, 2022 to September 3, 2022) based on BA.5. Vaccination history was classified based on the final vaccination history 14 days before the COVID-19 diagnosis. In the case of Janssen, this was considered as receiving the second dose after receiving the first dose. To understand the scale and characteristics of the occurrence of severe and critical patients and deaths, demographic characteristics, including sex and age, vaccination rate, and incidence status by reported region according to the epidemic periods, were calculated based on the date of diagnosis confirmation. In addition, to understand the severity of COVID-19 according to the epidemic periods, the severity was divided into two levels to calculate the case severity rate (CSR) and case fatality rate (CFR) of each epidemic period and week. CSR was calculated as the proportion (%) of severe or critical patients among confirmed patients during the relevant periods (epidemic periods and weeks). CFR was calculated as the proportion (%) of deaths among confirmed patients during the relevant periods (epidemic periods and weeks). In addition, to understand the scale of deaths relative to the total population, mortality rates by periods were calculated on a weekly average and per million people for the proportion of deaths in the total population. To compare the severity by age, the age group was divided into 10-year-old units to calculate the severity, fatality, and mortality rates. We used the Excel 2016 program (Microsoft, Redmond, WA, USA) for all of the analyses.

Results

From COVID-19 first reported to now, September 3, 2022, 23,496,820 confirmed cases were reported in the ROK, of which 26,472 (0.11%) were in severe or critical conditions and 27,471 (0.12%) died. Among the patients who were recognized as having severe or critical conditions after being diagnosed with COVID-19, 7,507 died, and 46,436 (0.20%) progressed to severe or critical conditions or death in total.

1. Status of Patients with Severe or Critical Conditions

Of the 26,472 patients with severe or critical conditions confirmed during the COVID-19 outbreak, the highest number of patients with severe or critical conditions, which accounted for 40.7% (10,772) of all patients with severe or critical conditions, occurred during the Omicron BA.1/BA.2 dominant period (Table 1). Additionally, this period accounted for 78.6% of the total confirmed cases. Compared to the Delta variant dominant periods, the number of confirmed cases increased sharply (34.1 times) and the number of patients with severe or critical conditions increased (1.3 times) during the Omicron BA.1/BA.2 dominant period (Figure 1). However, due to the decrease in the severity of the Omicron variant, the increase in the number of patients with severe or critical conditions was low compared to the increase in confirmed cases. Males accounted for more than 56% of the total period, which was 13% more than females. The average age of the patients with severe or critical conditions gradually increased from 67.7 years (±13.7 years) before the Delta variant dominance to 74.6 years (±15.7 years) during the Omicron BA.5 dominant period. The proportion of patients over 80 years of age increased by 26.3%, from 20.3% prior to the dominance of the Delta variant to 46.6% during the Omicron BA.5 dominant period. Before the Delta variant dominant period, 97.3% were unvaccinated, whereas 73.1% were vaccinated with at least one dose during the Omicron variant dominant period due to the improving vaccination rate. The metropolitan area, including Seoul, Gyeonggi, and Incheon, accounted for 72.9% before the Delta variant dominance. However, as the proportion of confirmed cases in non-metropolitan areas increased during the Omicron variant dominant period, that of patients with severe or critical conditions increased from 25.0% before the Delta variant dominant period to 44.5%.

Figure 1. Weekly number of confirmed cases, severe/critical cases and deaths (as of September 3, 2022)

Table 1 . Characteristics of COVID-19a) severe/critical casesb) by period (as of September 3, 2022).

ClassTotalPre-Delta dominant periodDelta dominant periodOmicron dominant period
BA.1/BA.2BA.5
Total26,472(100.0)4,665(100.0)8,296(100.0)10,772(100.0)2,739(100.0)
Sex
Male15,303(57.8)2,792(59.8)4,775(57.6)6,184(57.4)1,552(56.7)
Female11,169(42.2)1,873(40.2)3,521(42.4)4,588(42.6)1,187(43.3)
Age
Average (±SD)69.9±15.767.7±13.766.0±15.472.7±15.874.6±15.7
0–9 yr103(0.4)0(0.0)6(0.1)77(0.7)20(0.7)
10–19 yr107(0.4)3(0.1)21(0.3)68(0.6)15(0.5)
20–29 yr303(1.1)44(0.9)129(1.6)108(1.0)22(0.8)
30–39 yr768(2.9)116(2.5)399(4.8)199(1.8)54(2.0)
40–49 yr1,398(5.3)298(6.4)664(8.0)356(3.3)80(2.9)
50–59 yr2,837(10.7)730(15.6)1,150(13.9)800(7.4)157(5.7)
60–69 yr5,966(22.5)1,240(26.6)2,217(26.7)2,090(19.4)419(15.3)
70–79 yr6,948(26.2)1,289(27.6)2,084(25.1)2,880(26.7)695(25.4)
≥80 yr8,042(30.4)945(20.3)1,626(19.6)4,194(38.9)1,277(46.6)
≥60 yrc)20,956(79.2)3,474(74.5)5,927(71.4)9,164(85.1)2,391(87.3)
Vaccination
None14,627(55.3)4,539(97.3)5,031(60.6)4,321(40.1)736(26.9)
1 dose1,100(4.2)118(2.5)580(7.0)347(3.2)55(2.0)
2 dose4,552(17.2)8(0.2)2,595(31.3)1,656(15.4)293(10.7)
≥3 dose6,193(23.4)0(0.0)90(1.1)4,448(41.3)1,655(60.4)
Region
Metropolitan area17,279(65.3)3,402(72.9)6,184(74.5)6,172(57.3)1,521(55.5)
Seoul8,118(30.7)1,876(40.2)3,348(40.4)2,348(21.8)546(19.9)
Gyeonggi7,115(26.9)1,238(26.5)2,255(27.2)2,845(26.4)777(28.4)
Incheon2,046(7.7)288(6.2)581(7.0)979(9.1)198(7.2)
Non-metropolitan area9,068(34.3)1,166(25.0)2,085(25.1)4,599(42.7)1,218(44.5)
Busan1,493(5.6)156(3.3)433(5.2)738(6.9)166(6.1)
Daegu1,266(4.8)240(5.1)258(3.1)626(5.8)142(5.2)
Gwangju532(2.0)65(1.4)70(0.8)305(2.8)92(3.4)
Daejeon591(2.2)71(1.5)168(2.0)275(2.6)77(2.8)
Ulsan440(1.7)75(1.6)99(1.2)200(1.9)66(2.4)
Sejong55(0.2)2(0.0)12(0.1)32(0.3)9(0.3)
Gangwon837(3.2)99(2.1)175(2.1)455(4.2)108(3.9)
Chungbuk532(2.0)64(1.4)138(1.7)268(2.5)62(2.3)
Chungnam903(3.4)97(2.1)226(2.7)411(3.8)169(6.2)
Jeonbuk464(1.8)58(1.2)81(1.0)257(2.4)68(2.5)
Jeonnam425(1.6)42(0.9)63(0.8)248(2.3)72(2.6)
Gyeongbuk541(2.0)94(2.0)100(1.2)277(2.6)70(2.6)
Gyeongnam850(3.2)88(1.9)235(2.8)419(3.9)108(3.9)
Jeju139(0.5)15(0.3)27(0.3)88(0.8)9(0.3)
Quarantine125(0.5)97(2.1)27(0.3)1(0.0)0(0.0)

Values are presented as number (%). SD=standard deviation. a)Severe/critical case: Patient who were treated with non-invasive ventilation, high flow oxygenation, invasive ventilation, Extracorporeal membrane oxygenation (ECMO), Continuous renal replacement treatment (CRRT) during quarantine from COVID-19. b)Number of confirmed cases (≥80): Pre-Delta dominant period 187,349 (6,085, 3.2%), Delta dominant period 500,572 (15,602, 3.1%), Omicron BA.1/BA.2 dominant period 18,457,796 (528,350, 2.9%), Omicron BA.5 dominant period 4,351,103 (153,356, 3.5%). c)Over 60s..



2. Deaths

Of the 27,471 deaths during the COVID-19 pandemic, 66.4% (18,252) occurred during the Omicron BA.1/BA.2 dominant period. The number of deaths increased (3.6 times) due to the surge in confirmed cases (34.1 times) during the Omicron BA.1/BA.2 dominant period. Still, the increase in the number of deaths was lower than that of confirmed cases due to the decrease in the severity of the Omicron variant (Table 2, Figure 1). Differences in sex across the periods were similarly within 5% for each variant dominance period. The average age was also similar, being in the range of 77.2–80.2 years. Still, by age group, the proportion of people over 80 years old increased from 52.5% (1,135 people) before the dominance of the Delta variant to 62.3% (11,379 people) during the dominance of Omicron BA.1/BA.2 and 59.9% (1,378 people) during the dominance of Omicron BA.5. The unvaccinated rate before the dominance of the Delta variant was 98.8%. However, during the dominant period of the Omicron variant, the unvaccinated rate was 29.0% due to the increase in vaccination rate. Before the dominance of the Delta variant, 61.7% of deaths occurred in the metropolitan area. During the dominance of the Delta variant, 74.3% of deaths occurred in the metropolitan area, with an increase in confirmed cases in metropolitan areas. Additionally, during the Omicron variant dominant period, 58.3% of the total deaths occurred in non-metropolitan areas due to the increase in confirmed cases in these areas, which was more than in the metropolitan areas.

Table 2 . Characteristics of COVID-19 deaths by period (as of September 3, 2022).

ClassTotalPre-Delta dominant periodDelta dominant periodOmicron dominant period
BA.1/BA.2BA.5
Total27,471(100.0)2,162(100.0)4,758(100.0)18,252(100.0)2,299(100.0)
Sex
Male13,437(48.9)1,091(50.5)2,478(52.1)8,677(47.5)1,191(51.8)
Female14,034(51.1)1,071(49.5)2,280(47.9)9,575(52.5)1,108(48.2)
Age
Average (±SD)79.5±12.278.4±11.477.2±12.280.2±12.279.5±12.6
0–9 yr31(0.1)0(0.0)3(0.1)24(0.1)4(0.2)
10–19 yr16(0.1)0(0.0)0(0.0)14(0.1)2(0.1)
20–29 yr68(0.2)5(0.2)10(0.2)47(0.3)6(0.3)
30–39 yr130(0.5)11(0.5)33(0.7)70(0.4)16(0.7)
40–49 yr376(1.4)20(0.9)78(1.6)242(1.3)36(1.6)
50–59 yr1,143(4.2)105(4.9)232(4.9)705(3.9)101(4.4)
60–69 yr3,200(11.6)284(13.1)816(17.2)1,874(10.3)226(9.8)
70–79 yr6,326(23.0)602(27.8)1,297(27.3)3,897(21.4)530(23.1)
≥80 yr16,181(58.9)1,135(52.5)2,289(48.1)11,379(62.3)1,378(59.9)
≥60 yra)25,707(93.6)2,021(93.5)4,402(92.5)17,150(94.0)2,134(92.8)
Vaccination
None12,429(45.2)2,137(98.8)2,645(55.6)6,981(38.2)666(29.0)
1 dose1,053(3.8)22(1.0)260(5.5)721(4.0)50(2.2)
2 dose4,946(18.0)3(0.1)1,786(37.5)2,919(16.0)238(10.4)
≥3 dose9,043(32.9)0(0.0)67(1.4)7,631(41.8)1,345(58.5)
Region
Metropolitan area13,780(50.2)1,335(61.7)3,537(74.3)7,950(43.6)958(41.7)
Seoul5,344(19.5)554(25.6)1,714(36.0)2,708(14.8)368(16.0)
Gyeonggi6,940(25.3)713(33.0)1,539(32.3)4,169(22.8)519(22.6)
Incheon1,496(5.4)68(3.1)284(6.0)1,073(5.9)71(3.1)
Non-metropolitan area13,675(49.8)815(37.7)1,217(25.6)10,302(56.4)1,341(58.3)
Busan2,403(8.7)130(6.0)244(5.1)1,872(10.3)157(6.8)
Daegu1,569(5.7)222(10.3)166(3.5)1,015(5.6)166(7.2)
Gwangju634(2.3)24(1.1)48(1.0)502(2.8)60(2.6)
Daejeon773(2.8)34(1.6)157(3.3)531(2.9)51(2.2)
Ulsan396(1.4)41(1.9)25(0.5)284(1.6)46(2.0)
Sejong43(0.2)1(0.0)3(0.1)34(0.2)5(0.2)
Gangwon1,007(3.7)56(2.6)65(1.4)763(4.2)123(5.4)
Chungbuk827(3.0)71(3.3)54(1.1)619(3.4)83(3.6)
Chungnam1,156(4.2)46(2.1)139(2.9)820(4.5)151(6.6)
Jeonbuk962(3.5)60(2.8)64(1.3)773(4.2)65(2.8)
Jeonnam645(2.3)18(0.8)29(0.6)473(2.6)125(5.4)
Gyeongbuk1,598(5.8)88(4.1)114(2.4)1,267(6.9)129(5.6)
Gyeongnam1,448(5.3)23(1.1)97(2.0)1,173(6.4)155(6.7)
Jeju214(0.8)1(0.0)12(0.3)176(1.0)25(1.1)
Quarantine16(0.1)12(0.6)4(0.1)0(0.0)0(0.0)

Values are presented as number (%). SD=standard deviation. a)Over 60s..



3. Trends in Case Severity and Fatality Rates

The case severity rates and case fatality rates during the pandemic was 0.20%, and the case fatality rate was 0.12%. These rates were the highest at 2.98% and 1.15%, respectively, before the Delta variant dominant period and lowest at 0.10% and 0.05%, respectively, during the Omicron BA.5 dominant period (Table 3, Figure 2). The case severity rate decreased from 2.98% before the dominance of the Delta variant to 2.14% during the Delta variant dominant period. It decreased further to 0.14% during the Omicron BA.1/BA.2 dominant period, which was one-fifteenth the rate during the Delta variant dominant period. It decreased to 0.10% during the Omicron BA.5 dominant period (Figure 2). The case fatality rate also decreased from 1.15% before the Delta variant dominant period to 0.95% during the Delta variant dominant period and 0.10% during the dominance of Omicron BA.1/BA.2, which was one-tenth the rate as when the Delta variant was dominant. During the Omicron BA.5 dominant period, the case fatality rate decreased to 0.05%, half of that during the Omicron BA.1/BA.2 dominant period.

Figure 2. Weekly case severity rate and case fatality rate (as of September 3, 2022)

Table 3 . Case severity rate and case fatality rate by variant dominant period (as of September 3, 2022).

ClassTotal
(Jan 20, 2020–
Sep 3, 2022)
Pre-Delta dominant period
(Jan 20, 2020–
Jul 24, 2021)
Delta dominant period
(Jul 24, 2021–
Jan 15, 2022)
Omicron dominant period
BA.1/BA.2
(Jan 15, 2022–
Jul 23, 2022)
BA.5
(Jul 24, 2022–
Sep 3, 2022)
Case severity ratea)0.202.982.140.140.10
0–9 yr<0.010.000.02<0.010.01
10–19 yr<0.010.020.04<0.01<0.01
20–29 yr0.010.150.190.01<0.01
30–39 yr0.020.450.560.010.01
40–49 yr0.051.040.970.020.02
50–59 yr0.122.261.910.060.04
60–69 yr0.325.313.580.190.11
70–79 yr0.9213.638.870.670.38
≥80 yr2.9725.4219.742.631.51
Case fatality ratea)0.121.150.950.100.05
0–9 yr<0.010.000.01<0.01<0.01
10–19 yr<0.010.000.00<0.01<0.01
20–29 yr<0.010.020.01<0.01<0.01
30–39 yr<0.010.040.04<0.01<0.01
40–49 yr0.010.070.110.010.01
50–59 yr0.040.310.360.030.02
60–69 yr0.131.141.160.100.04
70–79 yr0.535.574.400.450.19
≥80 yr2.3018.6514.672.150.90
Mortality rate (Weekly average, per 1,000.000)6.750.533.6913.097.42
0–9 yr0.100.000.030.240.18
10–19 yr0.040.000.000.110.07
20–29 yr0.130.010.060.260.15
30–39 yr0.250.020.200.390.40
40–49 yr0.580.030.381.100.73
50–59 yr1.680.151.073.021.95
60–69 yr5.660.504.569.695.26
70–79 yr21.592.0513.9638.8523.78
≥80 yr97.346.8343.43199.93108.95

Values are presented as %. 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 severity, fatality, and mortality rates by periods and age groups all increased with age, and there were differences in the level of severity change according to epidemic periods for each age group. During the transition from before the dominance of the Delta variant to the dominance of the Delta variant, the case severity rate increased among those in their 30s or younger and decreased among those in their 40s. The case fatality rate increased among those in their 60s or younger and decreased among those in their 70s. During the transition from the dominance of the Delta variant to that of the Omicron variant, severity and case fatality rates in all age groups decreased, with the largest relative decline among those in their 30s (0.56% → 0.01%, 1/61 times) and the smallest decline among those in their 80s (19.74% → 2.63%, 1/8 times) among adults over 20 years of age. The absolute risk decreased the most in the age group over 80 years at 17.11%. Regarding the case fatality rate, the relative risk also decreased the most among those in their 30s (0.045% → 0.003%, 1/17 times) and decreased the least among those in their 80s (14.67 → 2.15%, 1/7 times). The largest absoulte reduction in case fatality rate was among those over 80 years of age, with a decrease of 12.52%. During the Omicron BA.1/BA.2 dominant period, the severity and case fatality rates were less than 1% in all age groups except those 80 years of age and older. During the Omicron BA.5 dominant period, the case severity rate was less than 1% in all age groups except those 80 years of age and older, and the case fatality rate was less than 1% in all age groups.

The mortality rate was the highest at an average of 13 per million per week due to the explosive increase in confirmed cases during the Omicron BA.1/BA.2 dominant period. The absolute risk also increased sharply with age, with a weekly average of 200 death per million people during the Omicron BA.1/BA.2 dominant period for those over 80 years of age and 109 deaths per million during the Omicron BA.5 dominant period.

Discussion (Conclusion)

This report analyzed the trend of the severity of COVID-19 from the date of the first confirmed case of COVID-19 in the ROK to the latest at the time of writing (September 3, 2022). We categorized the patients by severity (severe or critical conditions and death), period, and demographic through monitoring the clinical status of COVID-19 cases. In the period before the dominance of the Delta variant, the case severity rate was 2.98%; it was up to 6.95% in its weekly rate. The increase and decrease were repeated in the first year of the COVID-19 outbreak but gradually remained constant from 2021. The Delta variant has been reported to be more transmissible and severe than the preexisting viruses [7]. Whereas, in the ROK, the severity of all age groups during the Delta variant dominant period decreased to 2.14%. When divided by age group, there were differences in the increase or decrease in severity. The case severity rate increased among those in their 30s or younger, and the case fatality rate increased among those in their 60s or younger.

On the other hand, during the period of dominance of the Omicron variant, a sharp decrease in severity in all age groups was found, which was consistent with a global decrease in the severity of the Omicron variant [8,9]. However, the Omicron variant is more transmissible than preexisting variants and acts via immune evasion. Thus, the number of confirmed cases increased sharply by more than 30 times on average per day during the Omicron BA.1/BA.2 dominant period compared to the Delta variant dominant period, leading to the increase in the number of patients with severe or critical conditions and deaths. However, due to the decrease in severity, this increase rate was lower than the increase rate of confirmed cases, with a 1.3-fold increase in severe or critical cases and a 3.8-fold increase in deaths. The absolute reduction in severity during the Omicron BA.1/BA.2 dominant period compared to the Delta variant dominant period in the adult age groups over 20 years old was greatest in the group over 80 years of age, though the relatively smallest decrease was among those over 80 years of age compared to other age groups. This suggests that severe or critical cases and deaths are mostly in elderly over 80 years of age, when the severity has decreased due to the Omicron variant, indicating that appropriate measures for elderly are more important than before.

While responding to COVID-19 in the ROK, the results of monitoring COVID-19 severity were used as evidence for establishing response strategy strategies by periods. In early 2020, the severity of the outbreak was unknown; therefore, all confirmed patients were hospitalized in isolation. Through monitoring the severity of the confirmed cases, asymptomatic and mild confirmed cases were separated and managed in Residential Treatment Centers and as inpatients, which distributed health and medical resources for treating severe cases on time. With the announcement of the roadmap for gradual return to normal in October 2021, the COVID-19 response strategy focused on curbing the occurrence of severe cases caused by COVID-19 infection. Accordingly, the number of new severe or critical cases was a key indicator in the risk assessment of COVID-19. In addition, the results of monitoring severe or critical cases and deaths are used as primary data for the evaluation of vaccine effectiveness and the severity of a new variant of SARS-CoV-2.

The limitations of this report were as follows. First, the COVID-19 Severe Patient Surveillance System collects clinical information and registration reported by public health centers and medical institutions. Thus, cases in which clinical information is not reported in a timely manner or deaths are not captured, which may cause an underestimation. Second, since the data was classified based on the vaccination history entered into the immunization system, it was impossible to adjust the cases in which vaccination history was incorrectly entered. Third, this report was a result of analyzing only crude rates and did not adjust for differences in the demographic characteristics of confirmed cases, such as age and periods. However, it was possible to identify trends in the severity of confirmed cases with multiple characteristics for the purpose of viewing the severity of entire communities.

The severity of COVID-19 has decreased as the Omicron variant has become dominant, but as there is a large proportion of elderly among severe cases, the management of this population is becoming more important. In addition, the impact of the COVID-19 epidemic on various communities continues to change due to the emergence of new variants, the increase in vaccination, the decrease in the prevention effect over time after vaccination, the increase in reinfection due to immune evasion despite the patient’s previous infection history, and the increase in the number of unconfirmed infections in various communities. As such, it is necessary to closely monitor the severity of COVID-19 in these communities and to establish response strategies accordingly.

Declarations

Ethics Statement: Not applicable.

Funding Source: None.

Acknowledgments: We would like to thank National Medical Center for monitoring severe and critical patients of COVID-19, and Regional centers for Disease Control and Prevention for investigation of COVID-19 deaths.

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

Author Contributions: Conceptualization: BYR. Data curation: BYR. Formal analysis: BYR. Investigation: BYR, EJS, NYK, DHK, HJL. Methodology: BYR, SSK. Project administration: SSK. Resources: BYR, EJS, NYK, DHK, HJL, ARK. SYP, JHJ. Software: BYR. Supervision: DHK. Validation: SSK, DHK. Visualization: BYR. Writing – original draft: BYR. Writing – review & editing: SSK, DHK.

Fig 1.

Figure 1.Weekly number of confirmed cases, severe/critical cases and deaths (as of September 3, 2022)
Public Health Weekly Report 2022; 15: 2873-2895https://doi.org/10.56786/PHWR.2022.15.47.2873

Fig 2.

Figure 2.Weekly case severity rate and case fatality rate (as of September 3, 2022)
Public Health Weekly Report 2022; 15: 2873-2895https://doi.org/10.56786/PHWR.2022.15.47.2873

Table 1 . Characteristics of COVID-19a) severe/critical casesb) by period (as of September 3, 2022).

ClassTotalPre-Delta dominant periodDelta dominant periodOmicron dominant period
BA.1/BA.2BA.5
Total26,472(100.0)4,665(100.0)8,296(100.0)10,772(100.0)2,739(100.0)
Sex
Male15,303(57.8)2,792(59.8)4,775(57.6)6,184(57.4)1,552(56.7)
Female11,169(42.2)1,873(40.2)3,521(42.4)4,588(42.6)1,187(43.3)
Age
Average (±SD)69.9±15.767.7±13.766.0±15.472.7±15.874.6±15.7
0–9 yr103(0.4)0(0.0)6(0.1)77(0.7)20(0.7)
10–19 yr107(0.4)3(0.1)21(0.3)68(0.6)15(0.5)
20–29 yr303(1.1)44(0.9)129(1.6)108(1.0)22(0.8)
30–39 yr768(2.9)116(2.5)399(4.8)199(1.8)54(2.0)
40–49 yr1,398(5.3)298(6.4)664(8.0)356(3.3)80(2.9)
50–59 yr2,837(10.7)730(15.6)1,150(13.9)800(7.4)157(5.7)
60–69 yr5,966(22.5)1,240(26.6)2,217(26.7)2,090(19.4)419(15.3)
70–79 yr6,948(26.2)1,289(27.6)2,084(25.1)2,880(26.7)695(25.4)
≥80 yr8,042(30.4)945(20.3)1,626(19.6)4,194(38.9)1,277(46.6)
≥60 yrc)20,956(79.2)3,474(74.5)5,927(71.4)9,164(85.1)2,391(87.3)
Vaccination
None14,627(55.3)4,539(97.3)5,031(60.6)4,321(40.1)736(26.9)
1 dose1,100(4.2)118(2.5)580(7.0)347(3.2)55(2.0)
2 dose4,552(17.2)8(0.2)2,595(31.3)1,656(15.4)293(10.7)
≥3 dose6,193(23.4)0(0.0)90(1.1)4,448(41.3)1,655(60.4)
Region
Metropolitan area17,279(65.3)3,402(72.9)6,184(74.5)6,172(57.3)1,521(55.5)
Seoul8,118(30.7)1,876(40.2)3,348(40.4)2,348(21.8)546(19.9)
Gyeonggi7,115(26.9)1,238(26.5)2,255(27.2)2,845(26.4)777(28.4)
Incheon2,046(7.7)288(6.2)581(7.0)979(9.1)198(7.2)
Non-metropolitan area9,068(34.3)1,166(25.0)2,085(25.1)4,599(42.7)1,218(44.5)
Busan1,493(5.6)156(3.3)433(5.2)738(6.9)166(6.1)
Daegu1,266(4.8)240(5.1)258(3.1)626(5.8)142(5.2)
Gwangju532(2.0)65(1.4)70(0.8)305(2.8)92(3.4)
Daejeon591(2.2)71(1.5)168(2.0)275(2.6)77(2.8)
Ulsan440(1.7)75(1.6)99(1.2)200(1.9)66(2.4)
Sejong55(0.2)2(0.0)12(0.1)32(0.3)9(0.3)
Gangwon837(3.2)99(2.1)175(2.1)455(4.2)108(3.9)
Chungbuk532(2.0)64(1.4)138(1.7)268(2.5)62(2.3)
Chungnam903(3.4)97(2.1)226(2.7)411(3.8)169(6.2)
Jeonbuk464(1.8)58(1.2)81(1.0)257(2.4)68(2.5)
Jeonnam425(1.6)42(0.9)63(0.8)248(2.3)72(2.6)
Gyeongbuk541(2.0)94(2.0)100(1.2)277(2.6)70(2.6)
Gyeongnam850(3.2)88(1.9)235(2.8)419(3.9)108(3.9)
Jeju139(0.5)15(0.3)27(0.3)88(0.8)9(0.3)
Quarantine125(0.5)97(2.1)27(0.3)1(0.0)0(0.0)

Values are presented as number (%). SD=standard deviation. a)Severe/critical case: Patient who were treated with non-invasive ventilation, high flow oxygenation, invasive ventilation, Extracorporeal membrane oxygenation (ECMO), Continuous renal replacement treatment (CRRT) during quarantine from COVID-19. b)Number of confirmed cases (≥80): Pre-Delta dominant period 187,349 (6,085, 3.2%), Delta dominant period 500,572 (15,602, 3.1%), Omicron BA.1/BA.2 dominant period 18,457,796 (528,350, 2.9%), Omicron BA.5 dominant period 4,351,103 (153,356, 3.5%). c)Over 60s..


Table 2 . Characteristics of COVID-19 deaths by period (as of September 3, 2022).

ClassTotalPre-Delta dominant periodDelta dominant periodOmicron dominant period
BA.1/BA.2BA.5
Total27,471(100.0)2,162(100.0)4,758(100.0)18,252(100.0)2,299(100.0)
Sex
Male13,437(48.9)1,091(50.5)2,478(52.1)8,677(47.5)1,191(51.8)
Female14,034(51.1)1,071(49.5)2,280(47.9)9,575(52.5)1,108(48.2)
Age
Average (±SD)79.5±12.278.4±11.477.2±12.280.2±12.279.5±12.6
0–9 yr31(0.1)0(0.0)3(0.1)24(0.1)4(0.2)
10–19 yr16(0.1)0(0.0)0(0.0)14(0.1)2(0.1)
20–29 yr68(0.2)5(0.2)10(0.2)47(0.3)6(0.3)
30–39 yr130(0.5)11(0.5)33(0.7)70(0.4)16(0.7)
40–49 yr376(1.4)20(0.9)78(1.6)242(1.3)36(1.6)
50–59 yr1,143(4.2)105(4.9)232(4.9)705(3.9)101(4.4)
60–69 yr3,200(11.6)284(13.1)816(17.2)1,874(10.3)226(9.8)
70–79 yr6,326(23.0)602(27.8)1,297(27.3)3,897(21.4)530(23.1)
≥80 yr16,181(58.9)1,135(52.5)2,289(48.1)11,379(62.3)1,378(59.9)
≥60 yra)25,707(93.6)2,021(93.5)4,402(92.5)17,150(94.0)2,134(92.8)
Vaccination
None12,429(45.2)2,137(98.8)2,645(55.6)6,981(38.2)666(29.0)
1 dose1,053(3.8)22(1.0)260(5.5)721(4.0)50(2.2)
2 dose4,946(18.0)3(0.1)1,786(37.5)2,919(16.0)238(10.4)
≥3 dose9,043(32.9)0(0.0)67(1.4)7,631(41.8)1,345(58.5)
Region
Metropolitan area13,780(50.2)1,335(61.7)3,537(74.3)7,950(43.6)958(41.7)
Seoul5,344(19.5)554(25.6)1,714(36.0)2,708(14.8)368(16.0)
Gyeonggi6,940(25.3)713(33.0)1,539(32.3)4,169(22.8)519(22.6)
Incheon1,496(5.4)68(3.1)284(6.0)1,073(5.9)71(3.1)
Non-metropolitan area13,675(49.8)815(37.7)1,217(25.6)10,302(56.4)1,341(58.3)
Busan2,403(8.7)130(6.0)244(5.1)1,872(10.3)157(6.8)
Daegu1,569(5.7)222(10.3)166(3.5)1,015(5.6)166(7.2)
Gwangju634(2.3)24(1.1)48(1.0)502(2.8)60(2.6)
Daejeon773(2.8)34(1.6)157(3.3)531(2.9)51(2.2)
Ulsan396(1.4)41(1.9)25(0.5)284(1.6)46(2.0)
Sejong43(0.2)1(0.0)3(0.1)34(0.2)5(0.2)
Gangwon1,007(3.7)56(2.6)65(1.4)763(4.2)123(5.4)
Chungbuk827(3.0)71(3.3)54(1.1)619(3.4)83(3.6)
Chungnam1,156(4.2)46(2.1)139(2.9)820(4.5)151(6.6)
Jeonbuk962(3.5)60(2.8)64(1.3)773(4.2)65(2.8)
Jeonnam645(2.3)18(0.8)29(0.6)473(2.6)125(5.4)
Gyeongbuk1,598(5.8)88(4.1)114(2.4)1,267(6.9)129(5.6)
Gyeongnam1,448(5.3)23(1.1)97(2.0)1,173(6.4)155(6.7)
Jeju214(0.8)1(0.0)12(0.3)176(1.0)25(1.1)
Quarantine16(0.1)12(0.6)4(0.1)0(0.0)0(0.0)

Values are presented as number (%). SD=standard deviation. a)Over 60s..


Table 3 . Case severity rate and case fatality rate by variant dominant period (as of September 3, 2022).

ClassTotal
(Jan 20, 2020–
Sep 3, 2022)
Pre-Delta dominant period
(Jan 20, 2020–
Jul 24, 2021)
Delta dominant period
(Jul 24, 2021–
Jan 15, 2022)
Omicron dominant period
BA.1/BA.2
(Jan 15, 2022–
Jul 23, 2022)
BA.5
(Jul 24, 2022–
Sep 3, 2022)
Case severity ratea)0.202.982.140.140.10
0–9 yr<0.010.000.02<0.010.01
10–19 yr<0.010.020.04<0.01<0.01
20–29 yr0.010.150.190.01<0.01
30–39 yr0.020.450.560.010.01
40–49 yr0.051.040.970.020.02
50–59 yr0.122.261.910.060.04
60–69 yr0.325.313.580.190.11
70–79 yr0.9213.638.870.670.38
≥80 yr2.9725.4219.742.631.51
Case fatality ratea)0.121.150.950.100.05
0–9 yr<0.010.000.01<0.01<0.01
10–19 yr<0.010.000.00<0.01<0.01
20–29 yr<0.010.020.01<0.01<0.01
30–39 yr<0.010.040.04<0.01<0.01
40–49 yr0.010.070.110.010.01
50–59 yr0.040.310.360.030.02
60–69 yr0.131.141.160.100.04
70–79 yr0.535.574.400.450.19
≥80 yr2.3018.6514.672.150.90
Mortality rate (Weekly average, per 1,000.000)6.750.533.6913.097.42
0–9 yr0.100.000.030.240.18
10–19 yr0.040.000.000.110.07
20–29 yr0.130.010.060.260.15
30–39 yr0.250.020.200.390.40
40–49 yr0.580.030.381.100.73
50–59 yr1.680.151.073.021.95
60–69 yr5.660.504.569.695.26
70–79 yr21.592.0513.9638.8523.78
≥80 yr97.346.8343.43199.93108.95

Values are presented as %. 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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