IFNG and COVID-19: SARS-CoV-2-specific CD4+ T cells can be detected as early as on days 2–4 post-symptom onset, and rapid induction of functionally effective SARS-CoV-2-specific T cells is associated with prompt viral clearance and lower disease severity, while the delayed appearance of IFNγ-secreting cell is shown for patients with severe COVID-19 [13,14].