PBMCs of Pfizer/BioNTech BNT162b2 (n=8, triangles) and Moderna mRNA-1273 COVID-19 vaccines (n=11, circles) were stimulated with the Spike MPs corresponding to the ancestral reference strain (Wu, black) and the B.1.1.7 (UK, grey), B.1.351 (SA, red), P.1. (BR, orange) and CAL.20C (CA, light blue) SARS-CoV-2 variants. A) Percentages of AIM+ (OX40+CD137+) CD4+ T cells. B) Percentages of AIM+ (CD69+CD137+) CD8+ T cells. C) IFNγ spot forming cells (SFC) per million PBMCs D) IL-5 Spot forming cells (SFC) per million PBMCs. E) Percentages of IFNγ were calculated from the total IFNγ and IL-5 SFC per million PBMCs. Paired comparisons of the ancestral reference strain-based S MP versus each of the variants were performed by Wilcoxon test and are indicated by the p values in panels A-E. The data shown in panels A and B are also plotted showing the spike MPs titration (1 μg/mL, 0.1 μg/mL, 0.01 μg/mL) for CD4+ (F) and CD8+ (G) T cells in each SARS-CoV-2 variant. The geometric mean of the 0.1ug/mL condition is listed above each titration. In all panels, the bars represent the geometric mean.