Regarding the particularities of the COVID-19 vaccine immune response observed among the twins, Figure 4 shows the correlation between the major findings detected in the study, such as the humoral response (IgG antibodies), memory B cells activation, memory T cells activation, and cytokines produced by CD8+ T and CD4+ T (Th1 and Th2) cells over time. The gene discussed is CD8A; the disease is COVID-19.