IFNG and COVID-19: Interestingly, differences did not reach statistical significance when T cells were stimulated with peptides derived from the S1 subunit of the S protein alone (median IFN-γ 0.08 [IQR 0.02-0.40] IU/mL in COVID-19 negative group vs 0.01 [IQR 0.00-0.05] IU/mL in COVID-19 positive group, p=0.08; Figure 2A), but were statistically significant when both S1 and S2 subunit-derived peptides were used (median IFN-γ 0.09 [IQR 0.05-0.55] IU/mL in COVID-19 negative group vs 0.01 [IQR 0.00-0.05] IU/mL in COVID-19 positive group, p=0.01; Figure 2B).