These data suggest that prior COVID-19 increases the frequency of GPR56+ CD8 EM cells in males and these cells are more poised to make more IFNγ early after influenza vaccination, which together contributed to the higher IFNγ production in COVR-M (Extended Data Fig. 4f); consistent with this hypothesis, this was not observed in GPR56-cells. Here, CD8A is linked to COVID-19.