One such observational study by Hall et al. [31] evaluated humoral and cellular responses to two doses of BNT162b2 (COVID-19) mRNA-LNP vaccine indicated that delaying the boost up to 16 weeks before the second booster dose significantly enhanced anti-receptor-binding domain antibody titers as well as antigen-specific polyfunctional CD4+ and CD8+ T cells expressing IFN-γ and IL-2. This evidence concerns the gene CD4 and COVID-19.