FIGURE 3.

SARS‐CoV‐2‐peptide‐induced challenge responses involving highly poly‐functional CD4 T cells with a Th1 phenotype are persistently elevated within older individuals recovered from mild COVID‐19 for at least 9 months post recovery. (a) Comparison of polyfunctional CD4 T cells with 3–4 functional activation markers from individuals of different age groups at under 3, 6–9 and 9–12‐month recovery from mild COVID‐19 after 6‐h incubation with SARS‐CoV‐2 N, S1 or S2 peptide pools. Differences between groups were assessed using two‐way ANOVA with Tukey's multiple comparisons test *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. Data are represented as mean + 95% confidence intervals. Proportional analyses of the S1‐induced polyfunctional CD4 T‐cell responses can be seen in B with the mean values represented as a percentage of all three‐to‐four‐functional responses. Group <3‐month recovery 0–19 YO (years old) n = 14, 20–39 YO n = 45, 40–59 YO n = 63, 60+ YO n = 31. Group 6–9‐month recovery 0–19 YO n = 7, 20–39 YO n = 11, 40–59 YO n = 32, 60+ YO n = 8. Group 9–12 months recovery 0–19 YO n = 5, 20–39 YO n = 6, 40–59 YO n = 24, 60+ YO n = 7. (c) Correlation and simple linear regression of % of IFNγ+ IL‐2+ TNFα+ CD154+ CD4 T cells after SARS‐CoV‐2 peptide S1‐challenge against age in individuals recovered from mild COVID‐19 (<3 months post recovery n = 122 (left), 6–9 months post recovery n = 60 (middle) and 9–12 months post recovery n = 43 (right)). Linear regression shown with 95% confidence intervals and effect of age analysed via two‐tailed nonparametric Spearman correlation