• The levels of CD4+, CD8+ T cells, NK cells, and B cells were lower in severe cases. Whereas, TREG cells were found to be moderately increased in mild cases.• Higher levels of IL-2, IL-6, IL-10, and TNF-α were found in severe cases. Increase in IL-4 was observed in mild but not severe cases. Further, IL-2 and IL-6 were suggested as reliable indicators for disease severity.• Serum leves were inconsistent with low levels or unchanged in COVID-19 patients. The gene discussed is CD8A; the disease is COVID-19.