Focusing on the T cell response, we conducted a longitudinal study of infection-naïve and COVID-19 convalescent donors before vaccination and after their first and second vaccine doses, using a high-parameter CyTOF analysis to phenotype their SARS- CoV-2- specific T cells. Vaccine-elicited spike-specific T cells responded similarly to stim- ulation by spike epitopes from the ancestral, B.1.1.7 and B.1.351 variant strains, both in terms of cell numbers and phenotypes. For this study, a total of 120 specimens were analyzed by CyTOF. Each specimen included both CD4+ and CD8+ T cells. For each specimen, we gated separately on events corresponding to CD4+ T cells (live, singlet CD3+ CD19- CD4+ CD8-) and CD8+ T cells (live, singlet CD3+ CD19- CD4 CD8+), and exported the files as 240 individual FCS files. Included are 326 FCS files total from 165 different CyTOF specimens total. Half of the FCS files correspond to pre-gated live, singlet CD4+ T cells, and the other half of the correspond to pre-gated live, singlet CD8+ T cells. Eight donors vaccinated with the SARS-CoV-2 mRNA vaccines are represented with the data. Half are SARS-CoV-2 infection-naïve, and the other half are COVID-19 convalescents. Three longitudinal specimens are available for each donor: pre-vaccination, ~2 weeks after the first mRNA vaccination dose, and ~2 weeks after the second mRNA vaccination dose. For each specimen, 5 conditions were analyzed: baseline, and following 6-hour stimulation with overlapping 15-mer peptides from ancestral spike, B.1.1.7 spike, B.1.351 spike, or ancestral nucleocapsid. All stimulated samples were pre-gated on the spike-specific T cells based on IFNg production. In total, we analyzed CD4+ and CD8+ T cells from 11 donors x 3 timepoints x 5 conditions = 165 specimens.