Nevertheless, key differences were seen between the two groups, with spike-specific CD8+ populations in previously-infected individuals displaying fewer TCM and TTM T cells and a more terminal effector phenotype than naive vaccinees, even after omicron infection (p = 0.0017, Fig. 7a), as well as lower levels of CD27 and CCR2 expression than those seen in the naive group (Figs. S5 and S6). This evidence concerns the gene CD27 and infection.