Although vaccination resulted in the upregulation of genes related to the adaptive immune system and class I MHC-mediated antigen processing both in convalescents and COVID-19 naive individuals, the most striking upregulation of these genes occurred in CD4+ naive T cells from convalescents (~42.5% and 42.3% increase, respectively) (Fig. 5E). This evidence concerns the gene CD4 and COVID-19.