Differences in clinical characteristics and liver injury between patients diagnosed with the Omicron subvariant BA.5.2 and the prototype of SARS-CoV-2: a single center retrospective study

Background The purpose of this study was to investigate the differences between the clinical characteristics and the factors influencing liver injury in patients with the Omicron subvariant BA.5.2 (Omicron BA.5.2) and the prototype of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Methods Between December 30, 2019 and November 30, 2022, 157 patients infected with the SARS-CoV-2 prototype and 199 patients infected with the Omicron BA.5.2 were included in this case-control, single-center, retrospective study. Differences in clinical characteristics and liver injury between the Omicron BA.5.2 patients and the prototype patients were subsequently analyzed. Results None of the Omicron BA.5.2 patients reached the critical state, and showed relatively milder symptoms including fever, cough, headache, muscle soreness, nausea or vomiting, diarrhea, anorexia and hypoxia. The Omicron BA.5.2 had a lower effect on body temperature (T), white blood cell (WBC) count, hematocrit (HCT), C-reactive protein (CRP) level, D-dimer, finger pulse oxygen saturation (SpO2) and lung lesions. The differences in liver injury between the two groups were related to the severity of the disease, T, blood oxygen levels, albumin (ALB), CRP, and medication usage. Gender, body mass index, and CRP levels influenced liver damage in the Omicron BA.5.2 patients. In particular, CRP was an independent risk factor for liver injury. Because the severity of liver function damage was considerably low, only a small number of Omicron BA.5.2 patients required liver-protective treatment. Conclusion Liver injury is expected in the COVID-19 patients. The Omicron BA.5.2 patients showed milder symptoms of liver injury than the prototype patients. However, dynamic monitoring of liver function is warranted, especially for individuals presenting with elevated levels of CRP.

According to existing research, SARS-CoV-2 is the most well-known etiological agent for substantial respiratory pathology; furthermore, it may lead to several extrapulmonary manifestations, including gastrointestinal and liver injury, acute kidney injury, and neurological and psychiatric illnesses.Among these, liver injury is relatively the most common [12][13][14].COVID-19-associated liver injury occurs as a result of the cumulative effects of multiple factors.SARS-CoV-2 RNA expression has been detected in liver tissue, potentially causing hepatocellular lesions directly.Moreover, liver injury may be associated with drug-induced liver injury, hypoxic reperfusion, immune stress, and inflammatory factor storms [15][16].The data of 12 studies showed that the pooled prevalence of liver injury, the increased alanine aminotransferase (ALT), increased aspartate aminotransferase (AST), and decreased albumin (ALB) levels were 19%, 18%, 21%, and 6%, respectively [17].Additionally, liver injury is more prevalent in severe cases than in mild cases of COVID-19 [18].The Omicron variants reported here may not have been as severe as the previous episodes; however, additional evidence is needed to determine whether the Omicron variants are relatively more benign [10].The characteristics of the impact of the earliest COVID-19 (prototype) patients on liver function have been analyzed in the past [19].In this study, we aim to further analyze differences in clinical characteristics and liver injury between patients diagnosed with the Omicron BA.5.2 and the prototype.

Study design and patients
In the single-center retrospective study, patients admitted to the First Hospital of Yangtze University and infected with the prototype and Omicron BA.5.2 were included; thus, patients aged < 18 years, with serious underlying diseases, and pregnant women were excluded.

Data collection
The general information and clinical symptoms of all cases were collected.General information included gender, age, body weight, height, history of smoking and vaccination, and comorbidities-e.g., chronic obstructive pulmonary disease, hypertension, coronary heart disease and/or diabetes, viral hepatitis, and fatty liver.Clinical symptoms involved body temperature (T), finger pulse oxygen saturation (SpO 2 ), respiratory symptoms (e.g., fevers, cough, and sore throat, among others), and digestive symptoms (e.g., diarrhea and anorexia, among others).), C-reactive protein (CRP), D-dimer, IL-6, computed tomography (CT) imaging presentations, therapeutic drugs, and disease prognosis.Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to detect SARS-CoV-2 in samples collected via nasopharyngeal swabs.According to the central laboratory report specification prepared by the authors of the present study, the upper limits of normal (ULN) of ALT, AST, ALP, GGT, and LDH were 40, 42, 128, 50, and 240 U/L, respectively.In addition, the ULN of TB was 20.4 µmol/L, the lower limits of normal (LLN) of ALB was 35 g/L.Liver injury is defined as any exceedance of the ULN for liver function parameters including ALT, AST, ALP, GGT, LDH, and TB, or below the LLN for ALB.

Statistical analyses
Statistical analyses for all data were performed using the SPSS software version 22.0 (IBM Inc., Chicago, IL).Categorical variables were presented as numbers (percentages) and were analyzed using the Chi-Squared test or Fisher exact test.Measurement data were presented as mean ± standard deviation and were analyzed using the Student's t-test for intergroup comparisons.Multiple factors were analyzed using logistic regression.The histograms were drawn by GraphPad Prism 8. Furthermore, a two-sided P < 0.05 indicated statistical significance.

Epidemiological and clinical characteristics of the Omicron BA.5.2 and prototype patients
The Omicron BA.5.2 patients (n = 199) and prototype patients (n = 157) from December 30, 2019, to November 30, 2022, were included.The demographic and clinical characteristics are shown in Table 1.There were no significant differences between the two groups in terms of gender, age, smoking history, and comorbidities (coronary heart disease, hypertension, pulmonary disease, and liver disease) (P > 0.05) .

Influencing factors of abnormal liver function in the Omicron BA.5.2 and prototype patients
We discussed the probable reasons for the differences in liver damage between the Omicron BA.5.2 patients (n = 26) and the prototype patients (n = 77).No significant differences were noted in terms of gender (P = 0.106), age (P = 0.619), and comorbidities (P = 0.069).The Omicron BA.5.2 patients were vaccinated, and none of them were critically ill (P < 0.001).The SpO 2 (P = 0.027) and ALB (P < 0.001) levels in the prototype patients were significantly lower than the Omicron BA.5.2 patients, and the temperature (P = 0.041) and CRP levels (P = 0.001) were significantly higher.However, D-dimer levels showed no significant difference (P = 0.161).Besides, the prototype patients received a wider variety of medications.Hormones (P < 0.001), antibiotics (P < 0.001), and chloroquine (P = 0.019) may be associated with liver damage, there was no difference in liver damage among patients using Chinese patent medicine (P = 0.115 ) (Table 5).

Discussion
Currently, Omicron has become the dominant global epidemic strain owing to its significant immune escape and higher transmissibility.The Omicron BA.5 variant has become the most prevalent Omicron subvariant worldwide [9, 21−22]; however, the characteristics of liver damage caused by the Omicron BA.5 variant remain unclear.In the study, we aim to examine and compare the clinical features, laboratory test results, and liver injury associated with the Omicron BA.5.2 patients to those of the prototype patients.
Several countries reported mild symptoms related to the Omicron strain with a mortality rate of 0.13-0.5%,which was 83-90% lower than that of the prototype and other VOC [23 -24].The proportion of Omicron-VOC patients with asymptomatic was 16-47.5% [25][26].Furthermore, similar features were observed in the Omicron  The proportion of asymptomatic Omicron BA.5.2 patients was 31%.Conversely, nearly all the prototype patients presented with various symptoms.Our previous study demonstrated that more serious lung injuries were associated with disease exacerbation, lower blood oxygen, and more serious CT manifestations in prototype patients.The hospitalized patients infected with the Omicron BA.5.2 showed little oxygen depletion, and about two-thirds had no inflammatory response on lung CT, all patients showed mild or common manifestations.
The mortality rate of the prototype patients reached 7%, whereas no severe disease or death occurred in the Omicron BA.5.2 patients.This observation aligns with several studies suggesting a milder course for the Omicron.A nationwide data study in South Africa indicated that the risk of severe illness from Omicron infections reduced by 70% compared to earlier Delta infections [27].Similarly, a retrospective cohort study (Omicron and Delta cohorts) in the United States found that proportions of hospitalization, ICU admission, and mechanical ventilation among Omicron patients were significantly reduced [28].Interestingly, Kenrie P. Y. Hui et al. discovered that, 24 h after infection, the replication efficiency of the Omicron variant in human bronchi was 70 times higher than the prototype and Delta variant, but was 10 times lower in human lung tissue compared to the prototype [29].This could also explain an important reason why the majority of the Omicron-infected population experiences relatively mild conditions.In addition, the data showed that compared with the prototype, the Omicron BA.5.2 had less impact on the following parameters: WBC, PLT, HCT, PT, INR, D-dimer, and CRP.The Omicron BA.5.2 patients predominantly presented with lymphopenia, and a few patients had leukocytosis, thrombocytopenia, and hematocrit reduction.Serum CRP levels are closely related to inflammatory activity [30].D-dimer may also reflect an inflammatory condition and predict severe and fatal cases of COVID-19 with moderate accuracy [31].The levels of CRP and D-dimer in the Omicron BA.5.2 patients were significantly lower than in the prototype patients.Therefore, Omicron BA.5.2 patients had a lower inflammatory response than the prototype patients.Omicron BA.5.2 is thought to be less pathogenic than the prototype.
Studies have thoroughly explored the pulmonary lesions of patients with COVID-19; thus, the present study focused on liver injury.Compared with liver function indicators, the baseline levels of ALT, AST, TB, ALB, LDH, GGT, PA, and CHE as well as the proportion of  those abnormal indicators were lower in the Omicron BA.5.2 patients than in the prototype patients.Specifically, the proportion of ALT, AST, TB, GGT, and LDH levels exceeding 2ULN was significantly higher in the prototype patients, these findings indicate that the Omicron BA.5.2 was associated with milder liver function impairment and a lower risk of causing liver damage than the prototype.The differences in the severity of liver damage between Omicron BA.5.2 and prototype could be associated with factors such as the severity of the disease, T, blood oxygen levels, ALB and CRP.These factors might involve the different virological characteristics of virus mutant strains, hypoxia reperfusion dysfunction, immune imbalance, and cytokine storms [16].The foremost direct damage to the liver induced by SARS-CoV-2 is a plausible mechanism.Angiotensin-converting enzyme 2 (ACE2) has been shown to mediate SARS-CoV-2 infection, which is also expressed in cholangiocytes, hepatic sinusoidal endothelial cells (LSECs), and hepatocytes.Direct binding of the virus spike protein to ACE2 of targeted cells may result in hepatocyte and cholangiocyte injury and subsequent bile acid accumulation [16, 32−34].Omicron variants have been associated with the prototype through multiple mutations.The specific mechanisms underlying the possible effects of different strains require further elucidation.At present, no specific medicine exists for the treatment of SARS-CoV-2.In the early stages of the outbreak, hormones, antibiotics, arbidol, and Chinese patent medicine, among others were widely used, which may directly or indirectly cause drug-induced liver injury.However, it also has been reported that no liver injury secondary to Favipiravir was detected [35].In a previous, authors of the current study reported that hormones were associated with liver damage [19].Moreover, many regression studies have mentioned that the risk and proportion of liver injury were increased in patients with medium-tolarge doses of glucocorticoids (≥ 10 mg/d prednisolone or equivalent drugs), antibiotics, and other drugs [36-37] .Only a few of the hospitalized patients infected with the Omicron BA.5.2 were treated with Chinese medicine and antipyretic drugs.Compared with early treatment, the influence of drug therapy on liver function was significantly reduced.However, although Omicron has an immune escape, the vaccine continues to have some protective effects.Even if COVID-19 vaccinations do not provide complete protection against the new variant, they will at least result in less severe infections and lower death rates [37].Compared with the prototype patients, the Omicron BA.5.2 patients exhibited less severe inflammation and near-normal blood oxygen levels.Consequently, factors such as immune stress, inflammatory factor storms, ischemia, and hypoxia had less effect on liver damage [38].According to the review, Omicron patients showed milder abnormal liver function.Furthermore, this article further explored the characteristics of abnormal liver function in Omicron BA.5.2 patients.The main manifestation of liver injury was the mild elevation of AST, ALT, and GGT, which was more likely to occur in male and obese patients.Age, T, ALB, D-dimer, blood oxygen, and therapeutic drugs had little impact on liver damage.Notably, CRP was an independent factor associated with Omicron BA.5.2 patients.Ultimately, a small number of patients required liver-protective treatment.However, patients with elevated CRP still require attention.
This study has some limitations.First, it is a single-center retrospective study with a relatively small sample.Second, the assessment of liver injury is not comprehensive enough, lacking evaluation indicators such as liver biopsy puncture and radiological evaluation.Additionally, as the understanding of the virus evolves, the treatment of patients is continually adjusted.Despite these limitations, our study has successfully revealed the clinical features and liver damage characteristics of the Omicron BA.5.2 patients, and conducted comparative analysis with the prototype patients.Large-scale, multi-center clinical data are still essential to fully comprehend the impact of different SARS-CoV-2 variants on liver function.

Conclusion
In conclusion, our study demonstrates that the Omicron BA.5.2 presents with milder symptoms and lower mortality rates compared to the prototype.The Omicron BA.5.2 patients exhibit less liver damage.Gender, BMI, and CRP may correlate with liver function impairment in the Omicron BA.5.2 patients, with CRP potentially predicting the occurrence of liver function impairment.Yet dynamic monitoring of liver function is necessary, especially among those with elevated CRP during treatment, to ensure proper management and adapt treatment strategies as needed.

BMI=
Body Mass Index, SpO2 = finger pulse oxygen saturation, T = temperature, ALB = albumin, WBC = white blood cell, IL-6 = Interleukin-6, PT = plasma prothrombin time, INR = International Normalized Ratio The COVID-19 diagnosis was established based on the New Coronavirus Pneumonia Prevention and Control Program (9th edition) published by the National Health Commission of China and the interim guidance from the WHO [19-20].A positive COVID-19 PCR test confirms diagnosis, leading to hospitalization and isolation treatment according to local policies.Nasopharyngeal swab samples from 356 patients who were tested at the Jingzhou Centers for Disease Control laboratory genetic sequencing of the virus were Omicron BA.5.2 and prototype from December 30, 2019, to November 30, 2022.

Table 1
Epidemiological and clinical characteristics of the Omicron BA.5.2 and prototype patients < 0.001) and more frequently presented with symptoms of headache (10.6% vs. 3.8%, P = 0.012) and sore throat (13.1% vs. 8.3%, P = 0.001) than the prototype patients.In total, among the prototype patients, there were 45 severe or critical cases and 11 deaths.However, none of the Omicron BA.5.2 patients were in a critical condition or had died(P < 0.001).

Table 2
Laboratory and radiological characteristics of the Omicron BA.5.2 and prototype patients 9 9 9

Table 4
Comparison of abnormal liver function indexes in the Omicron BA5.2 and prototype patients BA.5.2.A total of 199 the Omicron BA.5.2 patients and 157 the prototype patients were enrolled in the study.

Table 5
Influencing factors of abnormal liver function in the Omicron BA5.2 and prototype patients

Table 6
Influencing factors of liver injury in the Omicron BA.5.2 patients