CD4 and infection: When comparing the specific CD4+ and CD8+ T cells towards spike from the parental strain and Omicron subvariants between infection-naive and convalescent patients after vaccination, the median percentage of parental spike-specific CD4+ T cells was lower in infection-naive patients (Fig. 2c), whereas spike-specific CD8+ T-cell levels did not differ between the two groups (Fig. 2d).