CD8A and viral infectious disease: In addition to B-cell-associated humoral immunity, the cellular immunity mediated by TH1 and cytotoxic CD8+ T lymphocytes also plays a critical role in the control of viral infection.7,26–30 The failure in the induction of a protective humoral immunity by COVID-19 patients recovered from the asymptomatic or mild disease may indicate an alternative strong cellular immunity that protected these patients from developing severe disease.