CD4 and COVID-19: Overall, the highest frequencies of epitope-specific IFN-g-producing CD4+ and CD8+ T cells (determined as mean SFCs > 50 per 0.5 × 106 PBMCs fixed as threshold) were detected in the unvaccinated COVID-19 patients who developed less severe disease (i.e., severity 0, 1, and 2, Figs. 2B, Supplementary Fig. S2, and Supplementary Fig. S3).