Table 3 Summary of calibrated ID50 and ID80 titers from the Duke and Monogram labs and their fold-differences for Day 29 vaccinee sera and Day 57 vaccinee sera.

From: Calibration of two validated SARS-CoV-2 pseudovirus neutralization assays for COVID-19 vaccine evaluation

Calibrated ID50

Vaccine Day 29 (n = 27)

Vaccine Day 57 (n = 30)

Approach 1

Approach 2

Approach 3

Approach 1

Approach 2

Approach 3

Duke

 Mean (SD)*

15.9 (0.8)

185.8 (1.0)

284.2 (0.7)

353.9 (1.1)

3955.5 (1.0)

3426.3 (0.9)

 Median

17.5

227.4

307.5

374.1

5030.2

3582.3

 Range

3.1–110.3

22.1–1210.8

77.5–1344.5

3.6–1140.0

66.4–15,078.3

86.9–8757.2

Monogram

 Mean (SD)*

11.6 (1.0)

190.9 (0.8)

178.3 (1.0)

268.9 (1.0)

3911.0 (1.0)

4120.7 (1.0)

 Median

14.3

210.0

219.5

344.2

4128.0

5274.0

 Range

1.3–79.8

39.4–1257.3

20.0–1222.0

4.0–1062.5

45.3–12,208.5

62.0–16,280.0

Monogram versus Duke fold difference

 Mean (SD)*

0.7 (0.4)

1.0 (0.4)

0.6 (0.5)

0.8 (0.4)

1.0 (0.4)

1.2 (0.4)

 Median

0.7

1.0

0.7

0.7

1.0

1.2

 Range

0.3–1.9

0.4–2.9

0.2–1.5

0.3–1.7

0.4–2.2

0.7–3.0

Calibrated ID80

Vaccine Day 29 (n = 27)

Vaccine Day 57 (n = 30)

Approach 1

Approach 2

Approach 3

Approach 1

Approach 2

Approach 3

Duke

 Mean (SD)*

24.4 (0.8)

63.5 (0.8)

125.8 (0.6)

496.1 (0.9)

1460.2 (1.0)

1330.0 (0.7)

 Median

29.3

84.8

145.1

632.7

1680.3

1609.0

 Range

7.5–136.6

21.5–390.4

50.0–484.7

7.5–1883.8

21.5–5538.9

50.0–3779.6

Monogram

 Mean (SD)*

13.9 (0.8)

87.9 (0.8)

60.9 (0.8)

347.3 (1.0)

1636.7 (0.9)

1522.5 (1.0)

 Median

18.7

105.0

82.0

401.1

2072.5

1758.5

 Range

4.6–89.6

28.0–468.1

20.0–393.0

4.6–1365.0

28.0–5975.6

20.0–5984.0

Monogram versus Duke fold difference

 Mean (SD)*

0.6 (0.5)

1.4 (0.5)

0.5 (0.5)

0.7 (0.2)

1.1 (0.2)

1.1 (0.3)

 Median

0.6

1.3

0.5

0.7

1.1

1.2

 Range

0.2–2.3

0.4–3.8

0.2–1.5

0.4–1.2

0.7–1.8

0.4–2.3

  1. In Approach 1, titers from each lab are calibrated to the WHO International Standard using the arithmetic mean-based calibration factor, expressed in International Units per ml (IU50/ml for ID50; IU80/ml for ID80); in Approach 2, titers from each lab are calibrated to a common scale using an independent pool of clinical samples, assuming a bivariate normal distribution for the readouts from the two labs; in Approach 3, titers from the non-reference lab (Duke) calibrated to the reference lab (Monogram) using an independent pool of clinical samples, based on regressing titers from the reference lab on the non-reference lab.
  2. *Geometric mean of titers or titer ratios and standard deviation of the loge-transformed titers or titer ratios.
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