CD4 and COVID-19: A significant correlation between the percentage of SARS-CoV-2-specific IL-4+ mCD4+ T cells (regulating acquired antibody responses) and the magnitude of RBD-IgG titers within 12 months post vaccination was found in the COVID-19 convalescent patients with vaccination (Fig. 5a), supporting the association between antibody responses and CD4+ T cells in some long-term cohorts4,9,52.