Fig. 1: Lower induction and early contraction of spike-specific CD4⁺ T cells in older adults.

a, Absolute number of total and AIM⁺ (CD137⁺CD154⁺) CD4⁺ T cells in blood. Pre, Post1, Post2 and 3 mo represents the sampling point before vaccination, after the first dose, after the second dose and 3 months after the first dose, respectively. b, Frequency of AIM⁺ and cytokine⁺ CD4⁺ T cells. c, Correlation between the percentage of AIM⁺ CD4⁺ T cells before and after vaccination. d, Proportions of multiple cytokine-expressing CD4⁺ T cells after vaccination in adult and older adult group. The blue, orange and gray colors in pie charts depict the production of one, two and more than three cytokines, respectively. e, Correlations between the percentages of AIM⁺ CD4⁺ T cells and age of donors. f, MFI of FSC-A in AIM⁺ CD4⁺ T cells. In a, b and f, the center line and error bars indicate the median and IQR, respectively. In b, c and e, the dotted line indicates limit of detection (LOD). Statistical comparisons across cohorts were performed using the Mann–Whitney test. Spearman’s rank correlation (r_s) was used to identify relationships between two variables, with a straight line drawn by linear regression analysis. For correlation analysis, percentages of AIM⁺ CD4⁺ T cells were transformed into logarithmic values. NS, not significant. Blue, red and black characters represent the results of statistical test from adults (n = 107), older adults (n = 109) and both groups (n = 216), respectively.

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