Epidemiological and clinical features of SARS-CoV-2 Omicron variant infection in China: A retrospective study

doi:10.21203/rs.3.rs-2471447/v1

Background: A rapid increase in incidence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant occurred in Quanzhou City, Fujian Province, China, in March 2022. This study investigated the epidemiological and clinical features of SARS-CoV-2 Omicron variant (BA.2)-infected patients.

Methods: Epidemiological and clinical data of SARS-CoV-2 Omicron variant infected patients admitted to three designated hospitals in Quanzhou were collected and analyzed.

Results: Overall, 2,541 patients infected with BA.2, comprising 1,060 asymptomatic, 1,287 mild, and 194 moderate infections, were enrolled in this study. The percentage of moderate infections was higher in those aged ≥60 than in those aged <18 and 18-59. The median hospitalization duration was 17 (14-20) days. Among the 2,541 patients, 43.52% had a clear history of close contact. The vaccination rate for coronavirus disease was 87.92%, and the percentage of asymptomatic infections was higher in vaccinated patients than in unvaccinated patients. Moreover, 10.82% with underlying diseases, such as hypertension (5.94%) and diabetes mellitus (3.12%), had a higher percentage of moderate infections than those without underlying diseases. The three most common clinical manifestations among the patients were fever (27.47%), dry cough (25.19%), and sore throat (15.31%). The albumin-to-globulin (A/G) ratio and lymphocyte count decreased in the cases of mild and moderate infections, while procalcitonin, erythrocyte sedimentation rate, interleukin-6, D-dimer, and C4 levels increased. The pulmonary computed tomography findings for moderate infections were generally patchy and ground-glass opacities.

Conclusions: Advanced age, non-vaccination, and underlying comorbid disease are high-risk factors for disease progression in Omicron variant-infected patients, while dynamic monitoring of blood routine parameters, A/G ratio, and inflammatory indicators facilitate the prediction of disease progression.

Biological sciences/Biochemistry

Biological sciences/Cell biology

Biological sciences/Immunology

Biological sciences/Microbiology

Health sciences/Biomarkers

Health sciences/Diseases

Health sciences/Gastroenterology

Health sciences/Health occupations

Health sciences/Medical research

Health sciences/Risk factors

Health sciences/Signs and symptoms

SARS-CoV-2

Omicron

clinical features

epidemiology

vaccine

The Omicron variant in Quanzhou had a low median age, mild clinical manifestations, short hospitalization duration, and good prognosis without any severe infections or deaths.
Despite the relatively low virulence of the Omicron variant, unvaccinated older adults especially those with underlying comorbidities, are at high risk of suffering from both severe infection or death.
The predominance of mild infections in the unvaccinated patients suggested that COVID-19 vaccination is still protective against the Omicron variant.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continuously mutates and evolves, producing mutant strains such as Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2), and Omicron (B.1.1.529) with changing transmissibility, pathogenicity, and immune escape ability ¹. The World Health Organization received the first report of an infection with the SARS-CoV-2 Omicron variant in South Africa on November 24, 2021, and upgraded its classification to concern variants on November 26 of the same year ². Omicron variants have since spread rapidly to many countries and regions worldwide and are now the dominant strains, threatening human health and life ³. The mutants have high transmissibility with a shorter generation time and incubation period, as well as a stronger immune escape ability, posing serious challenges to the prevention and control of the coronavirus disease (COVID-19) pandemic ⁴. On March 13, 2022, a sudden outbreak of COVID-19 occurred in Quanzhou City, Fujian Province, China. Nucleic acid testing of clinical samples by the Quanzhou Center for Disease Control and Prevention (CDC) showed that the strain was a SARS-CoV-2 Omicron sublineage (BA.2). The strain was further analyzed by the Chinese CDC, and no highly-homologous sequences were detected in China's current SARS-CoV-2 sequence database. Few retrospective clinical studies on the SARS-CoV-2 Omicron variant have been reported in China. This study analyzed the epidemiological and clinical features of BA.2 infections that caused the current epidemic outbreak in Quanzhou, aiming to provide a scientific basis for clinical diagnosis and treatment of the disease and accurate prognostic prediction.

Ethics declarations.

Informed consent has been obtained from all subjects and/or their legal guardians. This study was approved by the Ethics Committee of The First Hospital of Quanzhou Affiliated to Fujian Medical University (Quan Yi Lun 2020; approval number: K004). Research was conducted in accordance with the relevant guidelines and regulations of the Chinese Health Commission on the prevention and control of COVID-19.

Source of cases

This study enrolled patients who had either asymptomatic infections or confirmed symptomatic infections of Omicron variant strain BA.2 and were admitted between March 13, 2022, and April 14, 2022, at the Chengdong Branch and Infectious Diseases Branch of Fujian Medical University Affiliated First Quanzhou Hospital, as well as at the Quanzhou "Huoweishan" Cabin Hospital. Patients with suspected COVID-19 recovered but re-tested positive for SARS-CoV-2, who had previously been infected with the novel coronavirus, who originated from regions other than Quanzhou, and whose medical records had significant missing information were excluded from this study. This study was approved by the Ethics Committee of Fujian Medical University Affiliated First Quanzhou hospital.

Diagnostic criteria

Those with an epidemiological history and clinical manifestations of novel coronavirus infections along with serological or pathogenic evidence were confirmed as having a confirmed diagnosis of COVID-19 according to the Novel Coronavirus Disease Treatment Protocol (Trial Version 9) ⁵ issued by the Office of the National Health Care Commission and Office of the State Administration of Traditional Chinese Medicine. According to clinical manifestations and auxiliary examinations, confirmed cases were classified as mild, moderate, severe, and critical. Asymptomatic infections were defined as testing positive for the novel coronavirus and having no associated clinical manifestations according to the Prevention and Control Plan for Novel Coronavirus Disease (Version 8) issued by the Integrated Group of the State Council for Joint Prevention and Control of Novel Coronavirus Disease Epidemic ⁶.

Data collection

Information on demographic characteristics, such as sex, age, body mass index, underlying disease, and vaccination status for COVID-19, as well as disease classification and clinical manifestations, was obtained. Auxiliary examinations, such as those assessing routine blood parameters, inflammatory markers, humoral immunity, T-lymphocyte subsets (absolute counts), coagulation, complete biochemical parameters, COVID-19 antibodies, quantitative reverse-transcription polymerase chain reaction (RT-qPCR) cycle threshold (CT) for nucleic acid testing, and pulmonary imaging findings (except in pregnant women) and post-treatment testing, within 48 h of admission were performed. Moreover, each case was evaluated whether western or traditional Chinese medical treatments were applied. The efficacy was evaluated by recording the time interval from testing positive to testing negative for SARS-CoV-2. Strict database management regulations were implemented to ensure data security and confidentiality.

Statistical methods

All statistical analyses were performed using SPSS 23.0 (IBM Corp., Armonk, NY, USA). Measurement data were statistically analyzed using the Kruskal-Wallis rank-sum test or the Mann-Whitney U test and expressed as medians (25th and 75th percentiles). Count data were subjected to the χ2 or Fisher exact test and expressed as percentages. Differences with a P-value of <0.05 were considered statistically significant.

Epidemiological, demographic, and clinical features

A total of 2,541 patients infected by SARS-CoV-2 Omicron sublineage (BA.2) were enrolled in this study, of whom 1,060 were asymptomatic, and 1,481 had a confirmed diagnosis of COVID-19. Of the confirmed cases, 1,287 were mild, and 194 were moderate, with no severe and critical cases. Of the 2,541 patients, 1,106 (43.52%), 901 (35.47%), and 34 (21.01%) had a confirmed, uncertain, and no history of contact, respectively. Regarding the number of infected patients (whether asymptomatic or confirmed cases), Fengze District had the highest number (46.80% and 55.15%), followed by Jinjiang City, Licheng District, Shishi City, Luojiang District, Nan'an City, Hui'an County, Dehua County, and Quangang District. Meanwhile, no confirmed cases were reported in Yongchun County and no Omicron variant infections in Anxi County (Figure 1). The percentage of patients who received the booster, second, and the first dose of the COVID-19 vaccine was 40.82%, 41.95%, and 5.16%, respectively, while the percentage of unvaccinated patients was 10.19%. Vaccinated patients had a higher percentage of asymptomatic infections (42.75%) than unvaccinated patients (36.29%, χ²=3.97, P=0.046) and a lower percentage of mild infections (49.69% vs 56.76%, χ²= 4.64, P=0.031). However, there was no significant difference in the percentage of moderate infections (7.56% vs. 6.95%, P=0.72) between the vaccinated and unvaccinated groups, with no association of the between-group difference or similarity to the number of doses of the COVID-19 vaccine.

As shown in Table 1, there were 1,218 male patients (47.93%). The percentage of male individuals among asymptomatic patients was 51.04% (541), which was higher than that of those with moderate infections, 41.75% (81). The age of the patients ranged from 1 to 97 years, with a median value of 35 (24-48) years, and infections were mainly concentrated in those aged 18-59 (76.34%). Patients aged <18 years (15.03%) mainly had mild infections (57.33%), which was relatively higher than those of the patients aged 18-59 and >60 years. Patients aged ≥60 (8.62%) had a higher percentage of asymptomatic (49.32%) and moderate infections (10.96%) than those belonging to the other two age groups. The median hospitalization duration was 17 (14-20) days, with the longest being 19 days for moderate infections, 17 days for mild infections, and the shortest for asymptomatic infections being 16 days. A total of 275 patients (10.82%) had at least one underlying comorbid disease, with a high percentage of hypertension (151 cases for 5.94%) and diabetes mellitus (81 cases for 3.12%), followed by coronary heart disease, malignancy, chronic liver disease, thyroid disease, connective tissue disease, and respiratory disease. The percentage of moderate infections was higher in patients with underlying comorbid disease than in those without (12.00% vs. 7.12%, χ2=8.26, P=0.004). The most common clinical manifestations in confirmed cases were fever (27.47%), followed by dry cough (25.19%), sore throat (15.31%), fatigue (12.20%), expectoration (10.82%), myalgia (10.74%), stuffy and runny nose (4.80%), anosmia of taste and smell (2.99%), diarrhea (2.56%), shortness of breath (1.02%), conjunctivitis (0.31%), and nausea and vomiting (0.19%) (Figure 1).

Auxiliary examinations within 48 h of admission

Abnormal alanine transaminase (ALT) levels and hypo-albuminemia were observed in 190 (7.48%) and 312 (12.28%) patients, respectively (Table 2). The lymphocyte count and albumin-to-globulin ratio (A/G) were higher in the asymptomatic cases than in the mild and moderate cases (all P<0.01), while the asymptomatic cases had lower C-reactive protein (CRP), complement C4, interleukin-6 (IL-6), prothrombin, globulin (GLB), and D-dimer levels than the mild and moderate cases (all P<0.05). White blood cell, neutrophil, and platelet counts; total bilirubin (TBIL), ALT, and gamma-glutamyl transferase (GGT) levels; and CD3⁺ and CD4⁺ T-cell counts were higher in the asymptomatic cases than in the mild cases (all P<0.01). Meanwhile, the asymptomatic cases had a lower international normalized ratio than the mild cases (P<0.001), as well as a lower erythrocyte sedimentation rate (ESR) and immunoglobulin level than the moderate cases (all P<0.01). Blood urea nitrogen levels were higher in the asymptomatic cases, and albumin (ALB) levels were higher in the mild cases than in the moderate cases (both P<0.05). The common imaging findings for the moderate cases were patchy opacities (61.34%) and ground-glass opacities (53.09%), followed by strip cord shadow (39.18%) and nodular shadow (14.95%).

Main treatment options

All patients received traditional Chinese medicine treatment. In addition, 33 (1.29%), 54 (2.13%), and 12 (0.47%) patients received conventional nasal cannula oxygenation, oral antibiotic therapy (e.g., x with moxifloxacin and y with cefdinir) due to consideration of bacterial co-infections, and antiviral therapy treatment with oseltamivir phosphate, respectively.

This retrospective clinical study involved many patients infected by the community-transmitted SARS-CoV-2 Omicron variant in China. The results showed that patients with SARS-CoV-2 Omicron variant COVID-19 in Quanzhou had a low median age, mild clinical manifestations, short hospitalization duration, and good prognosis without any severe infections or deaths associated with a high vaccination rate against the virus (87.92%). Despite the relatively low virulence of the Omicron variant, unvaccinated older adults, especially those with underlying comorbid diseases, were at high risk of suffering from both severe infection and death ⁷. The predominance of asymptomatic infections in the vaccinated patients in this study and that of mild infections in the unvaccinated patients suggested that COVID-19 vaccination is still protective against the Omicron variant and that this protective effect is independent of the number of vaccination doses.

Existing studies suggest that women have a lower susceptibility to SARS-CoV-2 due to the protective effects of the X chromosome and sex hormones ⁸ and that women with SARS-CoV-2 infections have a lower risk of death than men (hazard ratio 1.59, 95% confidence interval 1.53-1.65) ⁹. In contrast, this study showed that the percentage of infected male individuals was lower than that of infected female individuals (47.93% vs. 52.07%) and that the percentage of male individuals among patients with moderate infections was significantly lower than that of male individuals among patients with asymptomatic infections, suggesting that female individuals are more susceptible to the Omicron variant sublineage BA.2 and more likely to have moderate infections. Unlike those infected with the original SARS-CoV-2 strain, the median age of patients infected with the Omicron variant was relatively low, with a downward shift in the age of infection ^10-12. Although patients aged ≥60 accounted for only 8.62% of the enrolled population, they had a higher percentage of moderate infections than those aged <18 and 18-59, suggesting that older age is still an important factor influencing disease progression. Another independent risk factor for disease progression is underlying comorbid disease ¹³ rather than various mutations in the Omicron sublineage BA.2.2 ¹⁴. The role of underlying disease in the progression of Omicron infections was further highlighted by the fact that 10.82% of the patients in this study had comorbidities and that the percentage of moderate infections was higher in this sub-population than in the rest of the patients without pre-existing conditions.

In this study, 41.72% of the patients infected with the Omicron variant were asymptomatic, and the clinical manifestations of confirmed cases were relatively mild. The most common symptoms of confirmed cases were fever, dry cough, sore throat, fatigue, and muscle aches; meanwhile, anosmia of taste and smell, conjunctivitis, and nausea and vomiting were relatively rare, consistent with that reported in a South Korea-based study ¹⁵. The relatively high percentage of asymptomatic infections poses a great challenge to the prevention and control of the pandemic, with nucleic acid testing and COVID-19 antigen detection as the important tools for the timely identification of infected patients and dynamic monitoring of the disease ¹⁶. Although asymptomatic and mild infections do not lead to pulmonary imaging changes, pulmonary imaging plays an irreplaceable role in clinical diagnosis and staging. Similar to the original SARS-CoV-2 strain, infections of the Omicron variant also damage the lungs, which manifested as patchy and ground-glass opacities in computed tomography images, with most lesions distributed in the peripheral zone and the subpleural areas. The difference was that the pulmonary lesions in patients infected with the Omicron variant were significantly smaller or even nodular, consistent with that reported in a study in Italy ¹⁷. The main reason for this difference is that the Omicron variant has a reduced binding capacity to the TMPRSS2 protein, significantly reducing the amount of virus entering the lung cells ^{18, 19}.

Moreover, laboratory tests play an integral role in monitoring the severity of the disease and its treatment. Current studies have shown that decreased lymphocyte and increased neutrophil count are significantly and positively associated with mortality ²⁰. Although there were no fatalities in this study, it is apparent that lymphocyte counts were significantly reduced in moderate and mild infections compared with asymptomatic infections, which was consistent with that reported in a study in China ²¹. Inflammatory indicators of infection, such as PCT, ESR, IL-6, and D-dimer levels, are effective predictors of mortality in intensive care unit inpatients ²². PCT, ESR, IL-6, and D-dimer levels were progressively elevated during asymptomatic, mild, and moderate infections. In particular, the IL-6 level was significantly elevated, with 7.48% of infected patients having an IL-6 level of >1,000 mg/L and 2.32% of infected patients surpassing the upper limit (>5,000 mg/L). Meanwhile, CRP, ESR, and leukocyte count were not simultaneously elevated to a high level. This observation ruled out the possibility of bacterial infections and suggested that the over-activation of the IL-6 signaling pathway by the Omicron variants may be involved, while the specific mechanism should be further investigated. These results suggest that dynamic monitoring of blood routine parameters, especially lymphocyte count and inflammatory indicators of infection, is useful in predicting the severity of the disease.

The incidence of liver dysfunction in COVID-19 patients was reported at approximately 14-53% ²³, which was significantly higher than in this study (7.48%) and can be attributed to the milder infections and Omicron variant in this study. Although most infected patients had ALB, GLB, ALT, GGT, and TBIL levels within normal ranges, 12.28% still developed hypo-albuminemia, a condition that can be used as a marker to assess the severity of pulmonary capillary endothelial cell injury in infected patients ²⁴. Low ALB levels and high GLB levels in moderate infections led to a further decrease in the A/G ratio, and monitoring the A/G ratio helps determine the disease's prognosis. Serum ferritin and lactate dehydrogenase are considered predictors of disease severity and disease progression in SARS-CoV-2 infected patients ²⁵, while neither was associated with disease severity in Omicron variant-infected patients in this study. Moreover, this study did not observe acute kidney injury induced by the interaction of SARS-CoV-2 nucleoproteins with Smad3 signaling molecules ²⁶.

Several studies have demonstrated the presence of complement system activation in COVID-19 patients, as evidenced by a decrease in both complement C3 and complement C4 levels, as well as a significant correlation of the decrease with disease severity and high mortality ^{27, 28}. Complement C4 level dropped in only 2.94% of infected patients in this study but was progressively elevated during asymptomatic, mild, and moderate infections, suggesting that the increase in complement C4 level was associated with disease severity in Omicron variant-infected patients and that high complement C3 level is an independent risk factor for delayed hospital discharge in patients infected with the original SARS-CoV-2 strain ¹¹.

This study had some limitations. First, all the investigated infections originated only from the Quanzhou area, and there were no severe cases, making it impossible to describe all the epidemiological and clinical features of SARS-CoV-2 Omicron infections. Second, the incubation period, RT-qPCR CT for nucleic acid testing, and duration of symptoms of infected patients were not investigated. Third, all infected patients were treated with a traditional Chinese medicine decoction, and it was impossible to clarify the effect of the decoction on disease outcome.

In conclusion, this study showed that patients infected with the SARS-CoV-2 Omicron variant in Quanzhou had a high rate of novel coronavirus vaccination, mild clinical manifestations, short hospitalization duration, and good prognosis, with no severe case and death case. This study revealed to a certain extent, the basic characteristics and prognostic outcomes of Omicron variant infections, and the findings provide a reference for the prognostic prediction and medical resource allocation of Omicron variant infections.

Funding

This study was supported by the Major Health Research Project of Fujian Province (2021ZD01001), the Scientific and Technological Development Project of Central Government shall guide local (2021L3018), the Young and middle-aged Talents Training Project of Fujian Provincial Health Commission (2020GGA076), the Science and Technology Innovation Joint Project of Fujian province (2019Y9048).

Conflicts of interest

None declared

Availability of data and materials

All relevant information is provided in this current manuscript. If required, the data presented in this work can be shared by e-mail.

WHO. Tracking SARS-CoV-2 variants［EB/OL］ 2021-12-06 [Available from: https://www.who.int/.
Pal R, Yadav U. Resurgence of COVID-19 in India: time for introspection. Postgraduate medical journal 2022;98:e86-e87.
Ulloa AC, Buchan SA, Daneman N, Brown KA. Estimates of SARS-CoV-2 Omicron Variant Severity in Ontario, Canada. Jama 2022;327:1286-1288.
Dance A. Omicron's lasting mysteries: four questions scientists are racing to answer. Nature 2022;603:22-24.
National Health Commission of China. COVID-19 Diagnosis and Treatment Protocol (Trial Version 9). International Journal of Epidemiology and Infectious Diseases 2022;49:73-80.
Notice on the publication of COVID-19 Prevention and Control (Eighth edition). Gazette of the National Health Commission of People's Republic of China 2021:4-60.
Cheung P-HH, Chan C-P, Jin D-Y. Lessons learned from the fifth wave of COVID-19 in Hong Kong in early 2022. Emerging microbes & infections 2022;11:1072-1078.
Chen N, Zhou M, Dong X, et al. Epidemiological and clinical characteristics of 99 cases of 2019 novel coronavirus pneumonia in Wuhan, China: a descriptive study. Lancet (London, England) 2020;395:507-513.
Williamson EJ, Walker AJ, Bhaskaran K, et al. Factors associated with COVID-19-related death using OpenSAFELY. Nature 2020;584:430-436.
Bager P, Wohlfahrt J, Bhatt S, et al. Risk of hospitalisation associated with infection with SARS-CoV-2 omicron variant versus delta variant in Denmark: an observational cohort study. The Lancet Infectious diseases 2022;22:967-976.
Lin P, Chen W, Huang H, et al. Delayed discharge is associated with higher complement C3 levels and a longer nucleic acid-negative conversion time in patients with COVID-19. Scientific reports 2021;11:1233.
Wang S, Zou X, Li Z, et al. Analysis of Clinical Characteristics and Virus Strains Variation of Patients Infected With SARS-CoV-2 in Jiangsu Province-A Retrospective Study. Front Public Health 2021;9:791600.
Liu X-Q, Xue S, Xu J-B, et al. Clinical characteristics and related risk factors of disease severity in 101 COVID-19 patients hospitalized in Wuhan, China. Acta pharmacologica Sinica 2022;43:64-75.
Zhang X, Zhang W, Chen S. Shanghai's life-saving efforts against the current omicron wave of the COVID-19 pandemic. Lancet 2022;399:2011-2012.
Kim M-K, Lee B, Choi YY, et al. Clinical Characteristics of 40 Patients Infected With the SARS-CoV-2 Omicron Variant in Korea. Journal of Korean Medical Science 2022;37:e31.
Peeling RW, Heymann DL, Teo Y-Y, Garcia PJ. Diagnostics for COVID-19: moving from pandemic response to control. Lancet (London, England) 2022;399:757-768.
Okoye C, Finamore P, Bellelli G, et al. Computed tomography findings and prognosis in older COVID-19 patients. BMC Geriatr 2022;22:166.
Yu Y-Q, Herrmann A, Thonn V, et al. SMYD2 Inhibition Downregulates TMPRSS2 and Decreases SARS-CoV-2 Infection in Human Intestinal and Airway Epithelial Cells. Cells 2022;11.
Meng B, Abdullahi A, Ferreira IATM, et al. Altered TMPRSS2 usage by SARS-CoV-2 Omicron impacts infectivity and fusogenicity. Nature 2022;603:706-714.
Cai J, Li H, Zhang C, et al. The Neutrophil-to-Lymphocyte Ratio Determines Clinical Efficacy of Corticosteroid Therapy in Patients with COVID-19. Cell Metab 2021;33.
Wenhuang C, Yijian L, Hongbo H, et al. A Retrospective Study of the Epidemiologic and Clinical Characteristics of COVID-19 Among Hospitalized Patients in Quanzhou, China. Infectious Microbes and Diseases 2021;3.
Milenkovic M, Hadzibegovic A, Kovac M, et al. D-dimer, CRP, PCT, and IL-6 Levels at Admission to ICU Can Predict In-Hospital Mortality in Patients with COVID-19 Pneumonia. Oxidative medicine and cellular longevity 2022;2022:8997709.
Zhang C, Shi L, Wang F-S. Liver injury in COVID-19: management and challenges. The lancet Gastroenterology & hepatology 2020;5:428-430.
Wu MA, Fossali T, Pandolfi L, et al. Hypoalbuminemia in COVID-19: assessing the hypothesis for underlying pulmonary capillary leakage. Journal of Internal Medicine 2021;289:861-872.
Chen ATC, Coura-Filho GB, Rehder MHH. Clinical Characteristics of Covid-19 in China. The New England journal of medicine 2020;382:1860.
Wang W, Chen J, Hu D, et al. SARS-CoV-2 N Protein Induces Acute Kidney Injury via Smad3-Dependent G1 Cell Cycle Arrest Mechanism. Advanced Science (Weinheim, Baden-Wurttemberg, Germany) 2022;9:e2103248.
Zinellu A, Mangoni AA. Serum Complement C3 and C4 and COVID-19 Severity and Mortality: A Systematic Review and Meta-Analysis With Meta-Regression. Frontiers in immunology 2021;12:696085.
Fang S, Wang H, Lu L, Jia Y, Xia Z. Decreased complement C3 levels are associated with poor prognosis in patients with COVID-19: A retrospective cohort study. International immunopharmacology 2020;89:107070.

Table 1. Demographic, epidemiological, and clinical features of patients infected with the SARS-CoV-2 Omicron variant BA.2.

Characteristics	All patients (n = 2541)	Asymptomatic patients (n=1060)	Light patients (n=1287)	Ordinary patients (n=194)	χ²	P value
Sex, male (%)	1218 (47.93%)	541 (51.04%)	596 (49.31%)	81 (41.75%)	8.423	0.0148
Age, median (IQR), years	35 (24-48)	38 (27-51)	33 (22-45)	39 (27.75-51)	56.89	< 0.0001
Age groups, years
<18	382 (15.03%)	140 (36.65%)	219 (57.33%)	23 (6.02%)	45.54	< 0.0001
18-39	1124 (44.23%)	423 (37.63%)	625(55.60%)	76 (6.76%)
40-59	816 (32.11%)	389 (47.67%)	356 (43.63%)	71 (8.70%)
≥60	219 (8.62%)	108 (49.32%)	87 (39.73%)	24 (10.96%)
BMI, Median (IQR) (kg/m²)	22.52(19.81-25.39)	23.03(20.08-25.61)	22.22(19.27-25.21)	22.86(20.70-25.64)	14.869	0.001
Length of stay, median (IQR), years	17(14.0-20.0)	16(12.75-19)	17(14-20)	19(16-22)	66.35	< 0.0001
COVID-19 vaccination status
Unknown	48(1.89%)	11(19.64%)	30(53.57%)	7(12.5%)	17.87	0.0222
Unvaccinated	259(10.19%)	94(36.29%)	147(56.76%)	18(6.95%)
Partially	131(5.16%)	56(42.75%)	67(51.15%)	8(6.10%)
Vaccinated	1066(41.95%)	433(40.62%)	550(51.59%)	83(7.78%)
Boosted	1037(40.82%)	466(44.94%)	493(47.54%)	78(7.52%)
Underlying disease
Hypertension	151(5.94%)	74(49.01%)	57(37.7%)	20(13.25%)	13.939	0.001
Diabetes	81(3.19%)	34(42.00%)	43(53.10%)	4(4.90%)	0.896	0.634^a
Coronary heart disease	25(0.98%)	9(36.00%)	14(56.00%)	2(8.00%)	0.456	0.777^a
Malignant tumor	20(0.79%)	9(45.0%)	7(35.0%)	4(20.0%)	4.668	0.069^a
Chronic liver disease	18(0.71%)	2(11.10%)	14(77.80%)	2(11.10%)	7.196	0.015^a
Thyroid disease	15(0.59%)	3(20.0%)	9(60.0%)	3(20.0%)	4.954	0.074^a
Connective tissue disease	9(0.35%)	3(33.3%)	4(44.4%)	2(22.2%)	2.761	0.245^a
Respiratory disease	7(0.28%）	4(57.1%)	2(28.6%)	1(14.3%)	2.144	0.312^a
Signs and symptoms
Fever	698(27.47%)	-	622(89.11%)	76(10.89%)	5.670	0.0173^a
Dry cough	640(25.19%)	-	556(86.88%)	84(13.12%)	0.0006	0.9796
Pharyngalgia	389(15.31%)	-	346(88.95%)	43(11.05%)	1.939	0.1638
Fatigue	310(12.20%)	-	272(87.74%)	38(12.26%)	0.2437	0.6215
Expectoration	275(10.82%)	-	230(83.64%)	45(16.36%)	3.161	0.0754
Myalgia	273(10.74%)	-	243(89.01%)	30(10.99%)	1.309	0.2525
Stuffy and runny nose	122(4.80%)	-	109(89.34%)	13(10.66%)	0.6974	0.40375
Anosmia of taste and smell	76(2.99%)	-	66(86.84%)	10(13.16%)	0.00027	0.9876^a
Diarrhea	65(2.56%)	-	58(95.5%)	7(4.5%)	0.390	0.584^a
Shortness of breath	26(1.02%)	-	23(88.46%)	3(11.54%)	0.05664	1.000^a
Conjunctivitis	8(0.31%)	-	7(87.50%)	1(12.50%)	0.0021	0.9633^a
Nausea and vomiting	5(0.19%)	-	5(100.0%)	0	0.756	0.3845^a

Note: ^aFisher exact test.

Table 2. Laboratory and imaging examination results of patients infected with the SARS-CoV-2 Omicron variant BA.2

	All patients (n=2541)	Asymptomatic patients (n=1060)	Light patients (n=1287)	Ordinary patients (n=194)	χ2	P
Leucocytes (*10^9/L)	5.22(4.09-6.65)(n=1981)	5.55(4.36-7.06)(n=684)	5.00(3.93-6.39)(n=1116)	5.28(4.13-6.61)(n=181)	36.054	0.000
Neutrophil (*10^9/L)	2.82(1.94-4.00)(n=1981)	3.07(2.17-4.17)(n=683)	2.68(1.84-3.87)(n=1117)	2.82(2.08-4.29)(n=181)	21.390	0.000
Lymphocytes (*10^9/L)	1.19(1.09-2.04)(n=1982)	1.63(1.20-2.21)(n=684)	1.42(1.05-1.92)(n=1117)	1.46(1.01-1.95)(n=181)	38.379	0.000
Neutrophil-to-Lymphocyte ratio	1.77(1.18-2.99)(n=1953)	1.74(1.19-2.80)(n=667)	1.77(1.16-3.06)(n=1105)	1.86(1.28-3.05)(n=181)	1.654	0.437
Monocytes (*10^9/L)	0.55(0.41-0.72)(n=1980）	0.53(0.41-0.70)(n=683)	0.56(0.42-0.74)(n=1117)	0.55(0.41-.075)(n=180)	4.662	0.097
Platelet (*10^9/L)	216.00(177.00-261.00)(n=1981)	221.00(182.00-272.00)(n=683)	213.00(173.00-255.00)(n=1117)	213.00(174.05-265.00)(n=181)	12.445	0.002
Red blood cell	4.66(4.31-5.04)(n=1980)	4.67(4.36-5.05)(n=683)	4.66(4.29-5.04)(n=1117)	4.65(4.29-5.04)(n=181)	1.299	0.522
Procalcitonin（ng/ml）	4.30(0.08-6.10) (n=682)	4.30(0.06-5.70)(n=175)	4.40(0.09-6.40)(n=449)	4.50(0.08-5.80)(n=58)	4.421	0.110
C-reactive protein (mg/L)	3.05(0.53-5.68) (n=1956)	2.13(0.51-4.58)(n=661)	3.59(0.55-6.28)(n=1115)	3.90(2.10-7.92)(n=180)	65.119	0.000
Erythrocyte sedimentation rate (mm/H)	15.00(9.00-25.00)(n=1787)	14.00(8.00-23.00)(n=579）	15.00(9.00-25.00)(n=1037)	17.00(10.00-31.00)(n=171)	10.471	0.005
Interleukin-6（ng/L）	7.59(3.68-76.12)(n=1588)	5.73(2.81-22.57)(n=492)	8.65(4.02-103.75)(n=937)	10.84(4.39-199.10)(n=159)	36.200	0.000
Prothrombin time (S)	11.40(10.90-12.10)(n=1828)	11.30(10.80-11.90)(n=584)	11.50(10.90-12.30)(n=1070)	11.40(10.70-12.10)(n=174)	29.077	0.000
D-dimer (mg/L)	0.26(0.16-0.40)(n=1859）	0.23(0.14-0.36)(n=611)	0.26(0.16-0.43)(n=1073)	0.28(0.19-0.42)(n=175）	23.276	0.000
INR	1.02(0.97-1.07)(n=1826)	1.00(0.96-1.05)(n=611)	1.02(0.97-1.09)(n=1069)	1.01(0.96-1.07)(n=174)	30.781	0.000
Albumin (g/L)	43.20(40.90-45.20)(n=1966)	43.20(40.80-45.20)(n=676)	43.30(41.00-45.30)(n=1109)	42.50(40.25-44.65)(n=181)	7.049	0.029
Globulin (g/L)	26.70(24.20-29.50)(n=1967）	26.50(24.00-29.80)(n=677)	26.60(24.20-29.20)(n=1109)	28.10(25.35-30.40)(n=181)	13.312	0.001
Albumin-to-Globulin ratio	1.62(1.15-1.79)(n=1899）	1.63(1.46-1.80)(n=622)	1.63(1.46-1.80)(n=1097)	1.55(1.37-1.71)(n=180)	17.658	0.000
Alanine transaminase (U/L)	17.00(12.00-26.00)(n=1966)	18.00(12.00-28.00)(n=676)	16.00(11.00-25.00)(n=1109)	17.00(12.00-27.00)(n=181)	9.967	0.008
Aspartate aminotransferase (U/L)	23.00(19.00-30.00)(n=1967)	23.00(19.00-29.00)(n=676)	23.00(19.00-30.00)(n=1110)	23.00(19.00-30.00)(n=181)	4.080	0.130
Glutamyl transpeptidase(U/L)	20.00(14.00-35.00)(n=1966)	22.50(15.00-38.75)(n=676)	19.00(14.00-32.50)(n=1109）	21.00(15.00-37.00)(n=181)	16.562	0.000
Alkaline phosphatase(U/L)	70.00(56.00-92.00)(n=1966）	73.00(58.00-92.75)(n=676)	69.00(54.00-92.00)(n=1109)	68.00(56.00-86.50)(n=181)	5.663	0.059
Total bilirubin (μmol/L)	9.20(7.13-12.40)(n=1964)	9.70(7.70-13.50)(n=674)	8.90(6.80-11.80)(n=1109)	8.90(7.30-13.40)(n=181)	29.791	0.000
Blood urea nitrogen (mmol/L)	4.12(3.44-4.98) (n=1937）	4.23(3.49-5.11)(n=651)	4.09(3.43-4.95)(n=1106)	3.89(3.27-4.73)(n=180)	10.056	0.007
Creatinine (μmol/L)	59.20(47.90-74.30)(n=1937）	60.70(49.10-75.80)(n=651)	58.30(47.58-73.80)(n=1106)	58.90(49.63-72.30)(n=180)	3.325	0.190
Complement C3	0.89(0.77-1.01)(n=1507）	0.89(0.77-1.03)(n=475)	0.89(0.76-1.01)(n=877)	0.90(0.80-1.02)(n=155)	1.342	0.511
Complement C4	0.25(0.20-0.30)(n=1508）	0.24(0.19-0.29)(n=476)	0.25(0.21-0.30)(n=877)	0.26(0.22-0.31)(n=155)	9.660	0.008
Immunoglobulin-A	2.19(1.59-2.83)(n=1505）	2.19(1.63-2.82)(n=474)	2.19(1.54-2.81)(n=876)	2.30(1.74-3.02)(n=155)	4.350	0.114
Immunoglobulin-M	1.12(0.83-1.53)(n=1506）	1.12(0.79-1.55)(n=475)	1.13(0.83-1.52)(n=876)	1.07(0.88-1.53)(n=155)	0.341	0.843
Immunoglobulin-G	11.80(10.20-13.60)(n=1508)	11.70(9.98-13.60)(n=476)	11.70(10.10-13.50)(n=877)	12.70(10.70-14.90）(n=155)	15.225	0.000
Serum Ferritin(μg/L)	120.70(49.30-242.90)(n=1459)	140.70(57.98-253.63)(n=450)	110.20(44.15-233.05)(n=853)	126.70(59.33-250.79)(n=156)	5.411	0.067
CD3	1151.09(806.87-1582.38)(n=648)	1247.54(877.27-1712.52)(n=247)	1071.82(730.31-1433.89)(n=333）	1153.94(858.08-1576.71)(n=66)	15.367	0.000
CD4	628.78(419.59-891.08)(n=646)	697.00(505.06-942.87)(n=247)	560.14(384.32-815.31)(n=333)	646.87(470.32-911.36)(n=66)	19.186	0.000
CD8	426.02(287.33-591.60)(n=645)	464.48(300.99-663.13)(n=245)	416.78(254.93-560.78)(n=333)	458.73(312.61-584.30)(n=67)	5.813	0.055
CD4/CD8	1.47(1.12-1.89)(n=954)	1.47(1.17-1.97)(n=305)	1.46(1.10-1.85)(n=547）	1.52(1.07-1.97)(n=102)	2.902	0.234
B cell	145.28(85.63-245.02)(n=183)	196.97(40.24-314.40)(n=46）	142.67(86.00-217.45)(n=117)	163.45(86.54-279.07)(n=20)	2.250	0.325
NK cell	160.10(81.48-230.76)(n=180)	155.32(63.02-223.91)(n=46）	146.60(80.82-232.10)(n=115)	193.00(138.59-274.30)(n=19)	2.501	0.286
Lactate dehydrogenase	200.00(173.00-235.00)(n=1933)	197.00(170.00-231.00)(n=648)	200.00(173.00-239.00)(n=1105)	208.00(177.25-237.00)(n=180)	5.918	0.052
Uric acid	331.0(265.00-404.00)(n=1936)	336.00(268.75-407.00)(n=650)	328.50(261.00-404.00)(n=1106)	323.50(266.00-397.50)(n=180)	1.576	0.455
Patch shadow	-	-	-	119(61.34%)	-	-
Ground glass opacity	-	-	-	103(53.09%)	-	-
Strip cord shadow	-	-	-	76(39.18%)	-	-
Nodular shadow	-	-	-	29(14.95%)	-	-

No competing interests reported.

Epidemiological and clinical features of SARS-CoV-2 Omicron variant infection in China: A retrospective study

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Journal Publication

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Abstract

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Key Points

Introduction

Materials and methods

Results

Discussion

Declarations

References

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Additional Declarations

Status:

Journal Publication

Version 1