CD4 and infection: Besides antibodies, effector CD4 T and CD8 T cells have multiple roles in protecting against COVID-19, including (i) CD4 T cell-mediated activation of B cells to become antibody-producing plasma cells, and (ii) CD4 T and CD8 T cells responding to epitopes in multiple SARS-CoV-2 proteins including S, N, membrane, and non-structural proteins, controlling infection and reducing COVID-19 severity [6,20,93].