CD4 and COVID-19: More recently, Dan and colleagues measured circulating SARS-CoV-2 antigen-specific antibodies, memory B cells, and CD8+ and CD4+ T cells for >6 months postinfection in a cohort of patients with COVID-19 (n = 185) across a range of disease including asymptomatic, mild (non-hospitalized), moderate (hospitalized), and severe (hospitalized) (37).