We address whether T cell responses induced by different vaccine platforms (mRNA-1273, BNT162b2, Ad26.COV2.S, and NVX-CoV2373) cross-recognize early SARS-CoV-2 variants. T cell responses to early variants were preserved across vaccine platforms. By contrast, significant overall decreases were observed for memory B cells and neutralizing antibodies. In subjects ∼6 months post-vaccination, 90% (CD4⁺) and 87% (CD8⁺) of memory T cell responses were preserved against variants on average by AIM assay, and 84% (CD4⁺) and 85% (CD8⁺) preserved against Omicron. Omicron RBD memory B cell recognition was substantially reduced to 42% compared with other variants. T cell epitope repertoire analysis revealed a median of 11 and 10 spike epitopes recognized by CD4⁺ and CD8⁺ T cells, with average preservation > 80% for Omicron. Functional preservation of the majority of T cell responses may play an important role as a second-level defense against diverse variants.