Changes in activation-induced markers (AIMs) expression in T cells through flow cytometry upon stimulation with Mega Pools of peptides derived from SARS-CoV-2 in volunteers immunized with CoronaVac. (A) The gating strategy used to evaluate changes in the expression of AIMs upon stimulation of PBMCs is shown. PBMCs were stimulated with (B) MP-S, (C) MP-R, (D) MP-S + R, (E) MP-CD8A, (F) MP-CD8B, and (G) MP-CD8A + B for 24 h for samples obtained before the first dose, and 2 (second dose + 2 weeks) and 4 weeks (second dose + 4 weeks) after the second dose. Changes in the expression of AIMs for CD4+ T cells (OX40+ CD137+) were measured upon stimulation with (B) MP-S, (C) MP-R, and (D) MP-S + R. Changes in the expression of AIMs for CD8+ T cells (CD69+ CD137+) were measured upon stimulation with (E) MP-CD8A, (F) MP-CD8B, and (G) MP-CD8A + B. A total of 43 volunteers were evaluated for MP-S and MP-R and 21 volunteers for MP-CD8A and MP-CD8B. Data shown represent mean ± standard deviation. Statistical differences were evaluated by a Friedman test for repeated measures, followed by a post hoc Dunn test corrected for multiple comparisons against preimmune samples. n.s. = no statistical differences, *P < .05, **P < .005, ****P < .0001. Abbreviations: MP, Mega Pools; PBMC, peripheral blood mononuclear cell; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.