IFNG and COVID-19: Patients diagnosed with XLA showed a higher mean IFN-γ level to both peptide (S, S1, S+) mix (6.96 IU/mL in XLA patients compared to 2.05 IU/mL in healthy controls 95% confidence interval [CI] 3.11 – 6.7 p < 0.0001) and spike protein stimulation (2.83 IU/mL in XLA patients compared to 1.18 IU/mL in healthy controls (95% CI 0.42 – 2.87 p = 0.009), after primary COVID-19 vaccination compared to healthy controls (Figure 5).