CD8A and COVID-19: In contrast, similar frequencies of EBV BMLF-1280–288-specific CD8+ T cells were detected across the six groups of unvaccinated COVID-19 patients, regardless of disease severity, indicating that the decrease in the frequencies of T cells in severely ill COVID-19 patients specifically affected highly conserved and CCCs/SARS-CoV-2 cross-reactive T cells (Supplementary Figure 3A).