CD8A and COVID-19: Absolute counts of naïve CD4+ and naive CD8+ initial T-lymphocytes and CD8+ memory T-lymphocytes are decreased in patients in the critical group compared to patients in the mild group, and there was a negative correlation between the absolute counts of CD8+ initial T-lymphocytes, the CD4 + CD45RA+/CD4 + CD45RO+ ratio, and the CD8 + CD45RA+/CD8 + CD45RO+ ratio in the peripheral blood of patients with COVID-19 and the age of the patients.