Differences were found for the 29- to 79-year-old group, in which the frequency of naive CD8+ T cells was clearly reduced in COVID-19 patients, whereas percentages of effector, effector memory, and transitional memory cells were enhanced compared to those of healthy individuals, suggesting an ongoing CD8+ T cell response in COVID-19 patients (Fig. 2C). This evidence concerns the gene CD8A and COVID-19.