To confirm whether the T cell responses elicited by the ancestral strain in active COVID-19 patients could cross-react with the delta and omicron spike proteins, we tested and compared the T cell response in the PBMCs (n = 24) of active COVID-19 patients exposed to the ancestral strain of SARS-CoV-2, from V2 and V3, against the spike peptide pools of the ancestral, delta, and omicron variants (Figure 3). Here, CHMP5 is linked to COVID-19.