Pooled tetramer+CD8+ T cell precursor frequencies in influenza+ patients (mean ± SD, range: 2.62e-4±6.37e-4, 8.07e-7 to 3.56e-3) and influenza- patients (7.00e-5±8.11e-5, 8.38e-6 to 2.65e-4) were significantly higher 79-fold (p < 0.0001, Kruskal–Wallis test) and 21-fold (p = 0.0026, Kruskal–Wallis test), respectively, than pooled tetramer+CD4+ T cells (3.30e-6±3.20e-6, 6.19e-7 to 1.17e-5) (Supplementary Fig. 6d). Here, CD4 is linked to influenza.