Furthermore, it has been reported that CD4+ T-cell responses to SARS-CoV-2 are more prominent than CD8+ T-cell responses and are associated with controlling primary SARS-CoV-2 infection [13], making the amount of T-cell response a powerful tool to measure potential immunity from COVID-19 [7,18], highlighting that CD4+ response is characterized by the production of interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-ɑ), and interleukin-2 (IL-2) [14]. Here, CD4 is linked to COVID-19.