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The assessment of lymphocyte populations allows the monitoring, follow-up and treatment of patients with various infectious diseases. Acute respiratory syndrome caused by coronavirus (SARS-CoV-2), can lead to a decrease in circulating lymphocytes and cause disease progression and severity. We evaluated the association of CD4+/CD8+ T lymphocyte with COVID-19 disease severity in moderate and severe patients. 136 patients with COVID-19 from the moderate group (MG) and severe group (SG) were compared with a healthy group or control group (CG). CD3+, CD4+ and CD8+ T lymphocytes were quantified by flow cytometry and correlated to CD4+/CD8+ with sex, age, markers of inflammation (ferritin, C-reactive protein and D-dimer), lung damage and oxygen saturation. CD4+ and CD8+ T lymphocytes were significantly decreased in MG and SG (p<0.0001). The CD4+/CD8+ ratio showed association in MG with age (r=0.31; p=0.056), with lung damage (r=0.4; p=0.03) and in SG with total proteins (r=0.59; p=0.04) and D-dimer (r=0.57; p=0.03). The CD4+/CD8+ ratio is associated with disease severity, significantly affecting the cellular immune response.