Results: The absolute counts of T-lymphocytes and their subpopulations in the peripheral blood of COVID-19 patients were reduced, and the proportions of the cells in each subpopulation were imbalanced, with the absolute counts of T-lymphocytes and their subpopulations in peripheral blood of critically ill patients being lower relative to those of mildly ill patients, and the absolute counts of CD8+ initial T-lymphocytes in the peripheral blood of COVID-19 patients group being negatively correlated with the age of the patients. Here, CD8A is linked to COVID-19.