CD4 and COVID-19: We observed high variability in the magnitude of the SARS-CoV-2 CD4+ T cell response among the SARS-CoV-2–responding participants from both groups; although not statistically significant, the median response in COVID-19 cases was approximately 3-fold higher compared with non–COVID-19 controls (0.17%, IQR: 0.08%–0.55% and 0.05%, IQR: 0.03%–0.36%, respectively; Figure 2C).