Table 1.
Relationship Between SARS-CoV Neutralizing Antibodies and ELISA Titer
| ELISA Titer | PRNT Tested | Titer | % Neutralizers at FDA Minimal Level | % Neutralizers at FDA Recommended Level | |||
|---|---|---|---|---|---|---|---|
| <80 | 80 | 160 | >320 | ||||
| SARS-CoV-2 PRNT50 Titers | |||||||
| 160 | 13 | 6 | 4 | 2 | 1 | 53.8 | 23.1 |
| 320 | 49 | 21 | 10 | 7 | 11 | 57.1 | 36.7 |
| 960 | 51 | 11 | 15 | 7 | 18 | 78.4 | 49.0 |
| 2880 | 44 | 5 | 2 | 8 | 29 | 88.6 | 84.1 |
| Total | 157 | 43 | 31 | 24 | 59 | 72.6 | 52.9 |
| SARS-CoV-2 PRNT90 Titers | |||||||
| 160 | 13 | 11 | 2 | 0 | 0 | 15.4 | 0 |
| 320 | 50 | 36 | 9 | 5 | 0 | 28.0 | 10.0 |
| 960 | 52 | 28 | 10 | 10 | 4 | 46.2 | 26.9 |
| 2880 | 44 | 13 | 9 | 10 | 12 | 70.4 | 50.0 |
| Total | 159 | 88 | 30 | 25 | 16 | 44.6 | 25.8 |
Serum specimens from COVID-19 convalescent patients that screened Ab positive to SARS-CoV-2 RBD, were titered by ELISA with respect to reactivity to SARS-CoV-2 whole spike protein. Sera with ELISA titers ≥160 were tested for their ability to neutralize SARS-CoV-2 infection of Vero E6 cells. The neutralization titer is the inverse endpoint dilution of sera that could neutralize 50% (top) or 90% (bottom) of viral plaque formation. % Neutralizers at FDA recommended level have a neutralizing titer of 160 or greater. % Neutralizers at FDA minimal level have a neutralizing titer of 80 or greater.
Abbreviations: ELISA, enzyme-linked immunosorbent assay; FDA, Food and Drug Administration; PRNT, plaque reduction neutralization tests; RBD, receptor-binding domain; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.