CD8A and COVID-19: Overall, the highest frequencies of CCCs/SARS-CoV-2 cross-reactive epitope-specific functional IFN-γ-producing CD8+ T cells (mean SFCs > 50 per 0.5 × 106 PBMCs) were detected in the three groups of unvaccinated COVID-19 patients who presented little to no severe COVID-19 symptoms (i.e., severity 0, 1, and 2, Figures 2A, B).