In addition, after two vaccine doses, the anti-S1 IgG (Figure 3A), the neutralizing antibody levels (Figure 3B), IFNγ-secreting T-cell counts in ELISpot (Figure 3D), AIM+IFNγ+CD4+ and AIM+triple+CD4+ frequencies (Figures 5C, D), total AIM+CD8+T cells (Figure 6B), and AIM+TNFα+CD8+ T-cell frequencies (Figures 4C, D) increased to a greater extent among COVID-19-recovered older adults compared with COVID-19-naive older adults. The gene discussed is CD4; the disease is COVID-19.