its outbreak in December 2019. Unfortunately, both the confirmed cases and deaths related to COVID-19 continue to increase rapidly globally (1) .
Several epidemiological features of the human-to-human transmission and clinical characteristics of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been reported. Phylogenetic analyses have revealed that SARS-CoV-2 is closely associated at 88%, 79%, and 50% identity with the bat-SL-CoVZXC21 and bat-SL-CoVZC45 SARS-like coronaviruses, SARS-CoV, and MERS-CoV, respectively (2) . The disease onset frequently manifests with cough and fever. In a cohort of 1099 patients with COVID-19, only 43.8% (473/1081) presented with fever which was much lower than seen in patients infected with SARS-CoV and MERS-CoV (3) . More importantly, confirmed asymptomatic patients with had similar viral transmission dynamics, in terms of the viral load, as the symptomatic patients (4, 5, 6) . Consequently, asymptomatic patients with COVID-19 may complicate the prevention, diagnosis, and control of this disease (7) . Clinical laboratory findings such as lymphopenia, lower counts of of CD4+ T and CD19+ B lymphocytes, and increased lactate dehydrogenase and C-reactive protein (CRP) levels are commonly observed in patients with COVID-19, and cases with advanced age, coexisting disorders, or dyspnoea were associated with the severity of the disease (8, 9, 10) .
A follow-up study on the dynamics of the clinical laboratory features in patients fourth-week (2 nd follow-up) follow-ups as outlined by the guidelines (11) .
The SARS-CoV-2 virus shedding duration was defined as the interval from the day of being confirmed positive for SARS-CoV-2 to the first day when SARS-CoV-2 testing returns a negative result (at least two consecutive negative RT-PCR results) during hospitalisation (12) .
The protocol of this study was reviewed and approved by the Ethics Committee of Taizhou Hospital of Zhejiang Province (#K20200111), and written informed consent was obtained from all patients or guardians.
General descriptive analyses of the variables were performed. Comparisons of variables were analysed using either t-tests or Mann-Whitney U tests for continuous variables. The χ 2 test with Fisher's exact probability was performed for categorical variables. Covariate binary logistic regression analysis with the forward conditional method was performed for variables investigated as independent predictive factors for severe COVID-19. Receiver operating characteristics (ROC) curves for each variable were generated to evaluate the power of each variable in differentiating between severe and non-severe COVID-19. The cut-off value for the independent predictive factors was determined by Youden's index. Statistical analysis was performed using SPSS v.13.0 (SPSS, Inc., Chicago, IL, USA). A two-sided p value < 0.05 was considered statistically significant. Among the 146 patients, following discharge, 13 (8.9%) patients without COVID-19 symptoms were re-admitted to the hospital after testing positive for SARS-CoV-2 RNA. 12 patients were confirmed to be SARS-CoV-2 repositivity by the 1 st follow-up an one patients by the 2 nd follow-up. However, no significant difference was observed in viral re-positivity after discharge between patients with severe and non-severe COVID-19 (p = 0.349). Details of the clinical characteristics of COVID-19 patients are shown in Table 1 .
Detailed laboratory findings at different time points (admission, discharge, and follow-up at the second and fourth week) among COVID-19 patients, and comparison between severe and non-severe COVID-19 patients are shown in Table 2 .
On the day of admission, the neutrophil count (median: 4.7510 9 /L vs. 3. 
To assay the predictive value of the above-mentioned variables with a p value less than 0.05 on admission (patient age, BMI, WBC count, neutrophil, eosinophil, lymphocyte, and its subsets CD3+ T cell, CD4+ and CD8+ T cell and NK cell, IL-10, CRP, AST, GGT, albumin, pre-albumin, and albumin/globulin (A/G) ratio) in differentiating between severe and non-severe COVID-19, we used covariate binary logistic regression analysis with the forward conditional method. Results showed that CD8+ T cells (HR = 0.995; p = 0.056) and CRP levels (HR = 1.040; p =0.002) on admission were independent predictive factors for severe COVID-19 (Table 3) . The human-to-human transmission risks by asymptomatic patients with have been emphasised in previous studies (19, 20) . In this scenario, virus isolation in patients re-positive for SARS-CoV-2 is extremely necessary, to testify whether virus are reactivated and replicated, or only genetic material of the 'dead virus' in patients with SARS-CoV-2 re-positivity after discharge.
Various clinical laboratory findings during early stages of COVID-19 have helped the evaluation of disease severity and have been highly related to mortality (21, 22, 23, 24) . However, the predictive significance of these variables in differentiating patients with severe and non-severe COVID-19 is unknown. Using covariate binary logistic regression analysis, our data showed that the CRP levels on admission were an independent predictive factor for patients with severe COVID-19. This might help develop more proactive management for severe COVID-19. T cell depletion and dysfunction are associated with COVID-19 progression (10, 23) . Subpopulations of T cells such as CD4+ and CD8+ T lymphocytes were delicately balanced for host cellular immune responses against viral infection. The CD8+ cytotoxic T lymphocytes orchestrate cytotoxic anti-virus responses and kill virus-infected cells directly, whereas the CD4+ helper T lymphocytes are essential for B lymphocyte maturation, which can produce virus-specific antibodies to neutralise viral antigens (16) . In this context, the decreased CD8+ T cells observed are associated with longer SARS-COV-2 virus shedding duration (12) . Although the counts of the peripheral immune cells were recovered during the convalesce as our findings indicated, whether immune functions of these immune cells restored remain unknown.
In summary, our findings provided evidence that peripheral immune cells recovered during the course of the disease, and that the CRP levels on admission were 