CD4+ and CD8+ responses could be detected in all individuals in both groups within the first 21 days after the second dose, with the post-COVID-19 group showing significantly higher CD4+ response against Ag1 (median 3.4, IQR 0.7–6.6) compared to the uninfected group (0.7 IU/mL, IQR 0.3–1.8, p = 0.0357; Figure 1D). This evidence concerns the gene CD4 and COVID-19.