Background: T-cell immunity is essential to effectively combat the coronavirus disease-2019 (COVID-19). In this research, the absolute T-cell CD4 and CD8 counts by flow cytometry were measured and the CD4:CD8 ratio in COVID-19 infected individuals was assessed. This investigation will help researchers to better understand the immune reaction to COVID-19 infection leading to improved medical and diagnostic outcomes. Methods: Peripheral blood samples were taken from 26 critically sick and 26 non-critically sick COVID-19 individuals of comparable age and sex. Absolute WBC count, absolute lymphocyte count, and platelet count were checked and flow cytometry was performed to calculate the absolute CD4 and CD8 T cells counts. Results: The critically ill COVID-19 patients were older (p<0.001) than non-critically sick COVID-19 individuals. In patients who got critically ill, absolute lymphocyte count (p=0.004), absolute CD4 count (p=0.002) and absolute CD8 counts (p=0.014) were low. However, the CD4:CD8 ratio did not differ substantially across the groups (p=0.538). The two groups did not differ in terms of gender. Absolute monocyte count (p=0.01) and absolute eosinophil count (p=0.01) were reduced significantly in critically sick patients as compared to non-critically sick COVID-19 patients. Conclusion: When compared to COVID-19 patients who weren’t in critical condition, the absolute lymphocyte count, CD4 count, and CD8 count of critically sick COVID-19 patients were significantly lower. This revealed that the lack of adequate cellular immune responses in critically sick COVID-19 patients may be the cause of the disease severity.