Table 2.

Performance of QFN and serology assay at the suppliers’ thresholds compared to neutralization in non-infected individuals after the second dose

	Neutralization (PRNT50 ≥ 20)
	19A	Alpha	Beta	Delta
Sensitivity (95% CI)
QFN Ag1 (IFNγ ≥ 0.15 IU/ml)   QFN Ag2 (IFNγ ≥ 0.15 IU/ml)   QFN Ag1 + 2 (IFNγ ≥ 0.25 IU/ml)   Serology (IgG ≥ 8.5 BAU/ml)	1.00 (0.93–1.00) 0.98 (0.90–1.00) 1.00 (0.93–1.00) 1.00 (0.93–1.00)	0.98 (0.90–1.00) 0.96 (0.88–0.99) 0.98 (0.90–1.00) 1.00 (0.93–1.00)	1.00 (0.91–1.00) 1.00 (0.91–1.00) 1.00 (0.91–1.00) 1.00 (0.90–1.00)	0.96 (0.87–0.99) 0.94 (0.84–0.98) 0.96 (0.87–0.99) 1.00 (0.93–1.00)
Specificity (95% CI)
QFN Ag1 (IFNγ ≥ 0.15 IU/ml)   QFN Ag2 (IFNγ ≥ 0.15 IU/ml)   QFN Ag1 + 2 (IFNγ ≥ 0.25 IU/ml)   Serology (IgG ≥ 8.5 BAU/ml)	0.58 (0.32–0.81) 0.50 (0.25–0.75) 0.58 (0.32–0.81) 0.00 (0.00–0.24)	0.55 (0.28–0.79) 0.45 (0.21–0.72) 0.55 (0.28–0.79) 0.00 (0.00–0.26)	0.24 (0.12–0.42) 0.25 (0.13–0.43) 0.24 (0.12–0.42) 0.00 (0.00–0.12)	0.33 (0.15–0.58) 0.25 (0.10–0.50) 0.31 (0.14–0.56) 0.00 (0.00–0.20)
PPV (95% CI)
QFN Ag1 (IFNγ ≥ 0.15 IU/ml)   QFN Ag2 (IFNγ ≥ 0.15 IU/ml)   QFN Ag1 + 2 (IFNγ ≥ 0.25 IU/ml)   Serology (IgG ≥ 8.5 BAU/ml)	0.92 (0.82–0.96) 0.90 (0.80–0.95) 0.92 (0.82–0.96) 0.81 (0.70–0.89)	0.92 (0.82–0.96) 0.90 (0.80–0.95) 0.92 (0.82–0.96) 0.83 (0.71–0.90)	0.63 (0.50–0.74) 0.64 (0.52–0.75) 0.63 (0.50–0.74) 0.56 (0.43–0.67)	0.83 (0.72–0.91) 0.80 (0.68–0.88) 0.81 (0.70–0.89) 0.76 (0.64–0.85)
NPV (95% CI)
QFN Ag1 (IFNγ ≥ 0.15 IU/ml)   QFN Ag2 (IFNγ ≥ 0.15 IU/ml)   QFN Ag1 + 2 (IFNγ ≥ 0.25 IU/ml)   Serology (IgG ≥ 8.5 BAU/ml)	1.00 (0.65–1.00) 0.86 (0.49–0.99) 1.00 (0.65–1.00) /	0.86 (0.49–0.99) 0.71 (0.36–0.95) 0.86 (0.49–0.99) /	1.00 (0.65––1.00) 1.00 (0.65–1.00) 1.00 (0.65–1.00) /	0.71 (0.36–0.95) 0.57 (0.25–0.84) 0.71 (0.36–0.95) /
Fisher’s exact test
QFN Ag1 (IFNγ ≥ 0.15 IU/ml)   QFN Ag2 (IFNγ ≥ 0.15 IU/ml)   QFN Ag1 + 2 (IFNγ ≥ 0.25 IU/ml)   Serology (IgG ≥ 8.5 BAU/ml)	p < 0.0001 (****) p < 0.0001 (****) p < 0.0001 (****) p > 0.9999 (ns)	p < 0.0001 (****) p < 0.0009 (***) p < 0.0001 (****) p > 0.9999 (ns)	p = 0.0020 (**) p = 0.0015 (**) p = 0.0020 (**) p > 0.9999 (ns)	p = 0.0053 (**) p = 0.0532 (ns) p = 0.0074 (**) p > 0.9999 (ns)
Agreement
QFN Ag1 (IFNγ ≥ 0.15 IU/ml)   QFN Ag2 (IFNγ ≥ 0.15 IU/ml)   QFN Ag1 + 2 (IFNγ ≥ 0.25 IU/ml)   Serology (IgG ≥ 8.5 BAU/ml)	92.4% 89.4% 92.4% 81.0%	90.9% 87.9% 90.9% 82.5%	66.7% 68.2% 66.7% 55.6%	81.8% 77.3% 80.3% 76.2%
Cohen’s kappa (95% CI)
QFN Ag1 (IFNγ ≥ 0.15 IU/ml)   QFN Ag2 (IFNγ ≥ 0.15 IU/ml)   QFN Ag1 + 2 (IFNγ ≥ 0.25 IU/ml)   Serology (IgG ≥ 8.5 BAU/ml)	0.70 (0.45–0.94) 0.58 (0.30–0.85) 0.70 (0.45–0.94) 0.00 (0.00–0.00)	0.62 (0.34–0.89) 0.49 (0.19–0.79) 0.62 (0.34–0.89) 0.00 (0.00–0.00)	0.26 (0.09–0.43) 0.28 (0.10–0.45) 0.26 (0.09–0.43) 0.00 (0.00–0.00)	0.36 (0.09–0.64) 0.24 (0.00–0.48) 0.34 (0.07–0.60) 0.00 (0.00–0.00)

QFN QuantiFERON SARS-CoV-2 Starter Set®, IgG G-immunoglobulins, PPV positive predictive value, NPV negative predictive value, / data not available.