No correlation however was observed between the magnitude of the COVID-19 vaccine antibody response, in terms of serum anti-spike Receptor Binding Domain (RBD) IgG concentrations after either the second or third vaccine dose, and the percentage of spike-specific CD4+ T-cells at those times (Spearman's ρ = -0.09, P=0.41 for post-second dose; ρ = −0.11, P=0.32 for post-third dose; Figure 2B). This evidence concerns the gene CD4 and COVID-19.