Confirmed COVID-19 cases admitted to 2 hospitals of Guizhou from January 23, 2020 to March 20, 2020 were selected, 8 cases were from the People's Hospital of Qiandongnan Miao and Dong Autonomous Prefecture, 36 cases were from the Jiangjunshan Hospital of Guiyang. 44 cases were selected in the study. Included 23 males and 21 females, aged from 5 months to 51 years with a mean age of 31.40 ±12.91 years. 22 cases were mild COVID-19, and 22 cases were moderate COVID-19.

In line with the Chinese COVID-19 diagnostic and therapeutic regimen(trial 8th edition)4, The confirmed patients tested positive for viral nucleic acid. Mild Group

The clinical symptoms were mild, and no signs of pneumonia were found on imaging. Moderate group: Patients had fever or respiratory symptoms, and imaging showed signs of pneumonia.

Comply with any of the following: 1. The shortness of breath, adult respiratory frequency (RR)≥30 times/min, (If children were younger than 2 months, RR≥60 times/min;2 ~ 12 months old，RR≥ 50 times/min; 1 ~ 5 years old, RR≥40 times/min; >5 years old, RR≥30 times/min, excluding the effects of fever and crying). 2.At rest, oxygen saturation ≤93% when inhaling air.3.Arterial partial pressure of oxygen (PaO2)/oxygen absorption concentration (FiO2) ≤300mmHg (1mmHg=0.133kPa).4.The clinical symptoms were progressively aggravated, and pulmonary imaging showed a significant increase of >50% within 24 ~ 48 hours.

Mechanical ventilation was required or shock occurs4.

Within 7 days after the onset of clinical symptoms (fever or cough). If the patients weren't clinical symptoms, it was 7 days after tested positive for nucleic acid.

As shown in Table 1, Table 2, Figure 1 and Figure 2, There were no differences in The WBC and LYM in the 4th day and the 7th day between the two groups (t/U=-0.064, -0.747, -0.278, -0.416 P>0.05). WBC and LYM in the 1st day in moderate group was lesser than in mild group (U=-3.135, -2.013 P<0.05). WBC and LYM in the 1st day, the 4th day and the 7th day were no change in the mild group (t=0.755, -1.452, 0.268, 1.577 P>0.05). In moderate group, WBC and LYM in the 1st day was lesser than in the 4th day (t=-2.390, -5.171 P<0.05), the levels in the 4th day and the 7th day was no differences (t=1.052, 1.609 P>0.05).

The global outbreak of COVID 19 has overwhelmed global health systems and posed severe challenges to human health and safety7. As a new infectious disease, COVID-19 needs to continue to summarize the experience in prevention and treatment measures. Clinical monitoring index plays an important role in the diagnosis and evaluation of the disease. WBC and LYM are commonly used indicators for infection monitoring. Many studies have suggested that WBC and LYM can help diagnose and assess COVID-198910. But the dynamic changes of WBC and LYM are unknown in patients with different degrees of severity. This study explored the dynamic changes of WBC and LYM in patients with different degrees of severity and analyzed their clinical significance.

WBC is comprised of lymphocyte, basophil, neutrophils, eosinophils and monocytes. The main function of WBC is defense. Different types of WBC participate in the body's defense response in different ways. Normal or reduced WBC in patients with viral infection is part of the important characteristics11. WBC can assist in the diagnosis of COVID-19. Other studies have shown a certain correlation between WBC and prognosis1213. In this study, there was no dynamic change in WBC level in patients with mild COVID-19 at the early stage. The WBC level in the 1st day of moderate COVID-19 was lesser than that in the 4th day and the 7th day, shown that moderate COVID-19 produced a strong prophylactic response in the body at a very early stage. The WBC rebound may be an indication that the disease is under control if there is no bacterial infection, or that the body's need for a preventive response has weakened. The level of WBC in the 1st day in patients with moderate COVID-19 was lesser than that in patients with mild COVID-19, shown that the chemotaxis of WBC in patients with moderate COVID-19 was stronger than that in patients with mild covid-19 in the super early stage. It shows if severity of the disease in the early stage was more. The severe the body's defense response was strong.

One study suggest that both innate and adaptive immune responses are essential for controlling COVID-19 infection14. LYM is a class of immune cells, mainly involved in the body's specific immune response. Novel coronavirus can be used as an antigen to stimulate the body to produce a specific immune response, followed by immune damage. Some researchers have reported peripheral blood lymphocyte count reduction in patients with severe COVID-1915. The same findings were found at autopsy in patients who died. The number of lymphocytes in the spleen and hilum of the lung significantly decreased, and both CD4+T cells and CD8+T cells in lymph nodes decreased16. The cases in this study were COVID-19 mild and moderate cases. No significant change of LYM was observed in the mild group at the early stage, indicating that the immune damage of the mild patients was relatively light. The LYM in the 1st day was lesser than the 4th day, shown that a strong and specific immune response may occur in the early stage. The LYM in the 1st day in the moderate group was lesser than that in the mild group, shown that in the super early stage (less than 4 days). The specific immunity produced in the moderate group was stronger than that in the mild group. It is speculated that sustained and severe immune injury may be essential for the occurrence of severe cases.

WBC and LYM exist important clinical significance in patients with mild COVID-19 and moderate COVID-19. The value of WBC and LYM in severe COVID-19 and critical COVID-19 requires further study. For critically ill patients more than 7 days later,WBC and LYM may have profound changes. At the same time, WBC and LYM lack specificity and sensitivity. When using these indicators, comprehensive analysis is needed to improve the guiding value of clinical diagnosis and treatment. The disadvantage of this study is that relatively few cases have been collected and there is a lack of severe and critical cases.