Specifically, thirteen individual cross-reactive CD4+ T cell epitopes (Supplementary Fig. S2) and sixteen individual cross-reactive CD8+ T cell epitopes (Supplementary Fig. S3) from the selected ten highly conserved antigens were quantified in each of the six groups of COVID-19 patients using an ELISpot assay (i.e., number of IFN-γ-spot forming T cells or “SFCs”). Here, IFNG is linked to COVID-19.