Table 3.
SARS-CoV-2 S-RBD and full-length spike IgG titres and neutralising antibody activity in PCR positive and PCR negative seropositive participants
| Participants | 1:150 titre | 1:450 titre | 1:1350 titre | 1:4050 titre | 1: 12 150 titre | Mean (SEM)* | p value† | ||
|---|---|---|---|---|---|---|---|---|---|
| S-RBD | |||||||||
| PCR positive | 19 | 5 (26%) | 5 (26%) | 6 (32%) | 3 (16%) | 0 | 674·5 (181·1) | .. | |
| PCR negative | 170 | 6 (4%) | 49 (29%) | 81 (48%) | 27 (16%) | 7 (4%) | 1186·3 (86·2) | 0·017 | |
| Full-length spike protein | |||||||||
| PCR positive | 19 | 6 (32%) | 2 (11%) | 2 (11%) | 6 (32%) | 3 (16%) | 1202·6 (472·7) | ||
| PCR negative | 170 | 3 (2%) | 2 (1%) | 41 (24%) | 83 (49%) | 41 (24%) | 3723·7 (259·9) | p<0·0001 | |
| ID50 range‡ | .. | <20 | (20–40) | (40–80) | (80–160) | (160–320) | .. | .. | |
| Neutralisation | |||||||||
| PCR positive | 19 | 13 (68%) | 2 (11%) | 3 (16%) | 1 (5%) | 0 | 16·8 (3·1) | .. | |
| PCR negative | 54 | 9 (17%) | 10 (19%) | 19 (35%) | 15 (28%) | 1 (2%) | 48·2 (5·7) | p<0·0001 | |
Data are number of participants (%), unless otherwise specified. S-RBD and ID50 titres were determined as described in procedures. S-RBD=spike receptor-binding domain.
*
Mean (SEM) of titre denominators or ID50 values was computed after converting undetectable titre <20 to be 10.
†
Cochran-Armitage test for the trend.
‡
ID50 is the titre at which a 50% reduction in virus infection was observed.