Coronavirus disease 2019 (COVID-19) is a novel infectious viral disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Two consecutively negative SARS-CoV-2 viral RNA test ( interval ≥ 24 hours), improved respiratory symptoms and obvious absorption of inflammation in pulmonary imaging are the discharge criteria for COVID-19 patients. The clearance profile of viral RNA in the upper respiratory tract specimens, including nasopharyngeal swab and/or oropharyngeal swabs, is related to innate immune cells such as Natural Killer cells. A total of 168 patients were included for the study. In this cohort, non-severe and severe groups showed significant differences in white blood cells, neutrophils, lymphocytes, basophils and platelets counts, as well as in infection related parameters such as CRP and serum cytokine IL-6. For lymphocyte subsets tests at admission, the severe group displayed significantly lower cell counts than the non-severe group. Higher counts of total T cells, CD4 + T cells, CD8 + T cells, and NK cells in peripheral blood showed a significant correlation with the shorter time taken to obtain the first negative viral RNA test and first positive IgM/ IgG antibody test. The number of B cells was only correlated with time to achieve the first positive IgM/IgG test. The count of NK cells was also correlated with a higher level of IgG antibody (p = 0.025). The lymphocytopenia group had a significantly worse survival rate (p = 0.022) and a longer duration (p = 0.023) of viral shedding than the normal lymphocyte count group. A lower NK cell count correlates the most with the worse survival rate (p<0.001) and a longer duration (p<0.001) of viral shedding. This study suggests the potential value of allo-Natural Killer cell therapy as an universal COVID-19 treatment strategy.