CD4 and COVID-19: To determine whether CD4+ T cells regulate long-term humoral immunity in patients with COVID-19, we compared the estimated decay rates for 10 months between two groups of patients grouped by the frequency of IFNγ+TNF+CD4+ T cells responding to SARS-CoV-2 peptide pool stimulation followed by 10-day expansion: high-CD4+ group (frequency > 10%) and low-CD4+ group (frequency ≤ 10%).