Table 3.

Proposed thresholds to improve the performances of QFN and serology assay compared to neutralization in non-infected individuals after the second dose

ROC analysis		Neutralization (PRNT50 ≥ 20)
		19A				Alpha				Beta				Delta
		Se	Sp	PPV	NPV	Se	Sp	PPV	NPV	Se	Sp	PPV	NPV	Se	Sp	PPV	NPV
QFN Ag1
Threshold 1	0.15 IU/ml	1.00	0.58	0.92	1.00	0.98	0.55	0.92	0.86	1.00	0.24	0.63	1.00	0.96	0.33	0.83	0.71
Threshold 2	0.50 IU/ml	0.80	0.92	0.98	0.50	0.78	0.91	0.98	0.46	0.78	0.48	0.66	0.64	0.76	0.63	0.86	0.46
Threshold 3	2.00 IU/ml									0.43	0.97	0.94	0.57	0.34	1.00	1.00	0.33
QFN Ag2
Threshold 1	0.15 IU/ml	0.98	0.50	0.90	0.86	0.96	0.45	0.90	0.71	1.00	0.25	0.64	1.00	0.94	0.25	0.80	0.57
Threshold 2	0.70 IU/ml	0.80	0.92	0.98	0.50	0.78	0.91	0.98	0.46	0.81	0.52	0.68	0.68	0.76	0.63	0.86	0.46
Threshold 3	3.00 IU/ml									0.46	0.93	0.90	0.57	0.28	0.94	0.93	0.30
QFN Ag1 + 2
Threshold 1	0.25 IU/ml	1.00	0.58	0.92	1.00	0.98	0.55	0.92	0.86	1.00	0.24	0.63	1.00	0.96	0.31	0.81	0.71
Threshold 2	1.20 IU/ml	0.83	0.92	0.98	0.55	0.82	0.91	0.98	0.50	0.84	0.48	0.67	0.70	0.80	0.63	0.87	0.50
Threshold 3	4.60 IU/ml									0.46	0.93	0.90	0.57	0.36	0.94	0.95	0.32
Serology
Threshold 1	150 BAU/ml	1.00	0.42	0.88	1.00	1.00	0.46	0.90	1.00	1.00	0.15	0.52	1.00	1.00	0.33	0.83	1.00
Threshold 2	850 BAU/ml	0.77	0.92	0.98	0.48	0.75	0.91	0.98	0.44	0.80	0.57	0.70	0.70	0.75	0.73	0.90	0.48
Threshold 3	2500 BAU/ml									0.20	0.89	0.70	0.47	0.21	1.00	1.00	0.28

ROC receiver operating characteristic, Se sensitivity, Sp specificity, PPV positive predictive value, NPV negative predictive value, QFN QuantiFERON SARS-CoV-2 Starter Set®