CD4 and COVID-19: In addition to the expected stimulation of B cells, with a strong increase in B-cell percentage in peripheral blood and the production of specific antibodies, COVID-19 vaccination leads to the activation of T-cell-mediated immunity and to the differentiation of CD4+ T cells towards the Th1 response, which mediates proinflammatory functions aimed at the development of cell-mediated immune responses [18,19,20,21,22,23].