Volunteers who developed transient infection in quarantine had significantly lower baseline IFNγ ELISpot responses to the CD8+ T-cell epitope peptide pool compared with those who remained uninfected, with median responses of 12 (IQR 7–56) and 77 (44–128) spot-forming cells per million PBMC, respectively (p=0·011; figure 4A). Here, IFNG is linked to infection.