The preservation of cross-reactive CD4+ TH and CD8+ TC cell epitopes between SARS-CoV-2 variants, at least for S proteins [47,48,49,50,51] and early data from clinical protection against the Omicron variant [52,53,54], also suggests that previous infection or exposure to SARS-CoV-2 provides protection against developing more severe COVID-19 during a subsequent infection. Here, CD4 is linked to COVID-19.