Furthermore, we found that the frequency of the spike-specific CD8+ T-cell subpopulation, which expresses simultaneously GZMA, GZMB and perforin, was lower 3 months after the second vaccination than at 1 month, suggesting that although the mRNA vaccine induces CD8+ T cells that reduce COVID-19 severity, the effect may not be long-lasting. Here, GZMB is linked to COVID-19.