Table 5.
Seroconversion rates, anti-S IgG concentrations, and neutralising antibody titres.
| Age group |
p-value | ||||
|---|---|---|---|---|---|
| 18–39 N = 64 | 40–59 N = 50 | 60–75 N = 74 | |||
| Binding antibody by ELISA (ng/ml) | |||||
| Week 2 post-vaccine 1 | Seroconversion, n (%) | 2 (3%) | 0 (0%) | 0 (0%) | 0.180 |
| GM titre (95% CI) | 655 (20–21469) | – | – | – | |
| Vaccine 2 | Seroconversion, n (%) | 11 (18%) | 3 (6%) | 3 (4%) | 0.021 |
| GM titre (95% CI) | 342 (163–719) | 724 (223–2355) | 983 (363–2663) | 0.335 | |
| Week 2 post-vaccine 2 | Seroconversion, n (%) | 52 (85%) | 36 (73%) | 59 (81%) | 0.333 |
| GM titre (95% CI) | 1473 (1125–1929) | 1185 (768–1829) | 1060 (764–1472) | 0.352 | |
| Week 4 post-vaccine 2 | Seroconversion, n (%) | 51 (88%) | 35 (74%) | 57 (78%) | 0.171 |
| GM titre (95% CI) | 1159 (844–1590) | 1132 (730–1754) | 1552 (1156–2084) | 0.333 | |
| Neutralising antibody (NT50) | |||||
| Week 2 post-vaccine 2 | Seroconversion, n (%) | 36 (59%) | 28 (57%) | 38 (52%) | 0.717 |
| GM dilution (95% CI) | 69 (46–102) | 65 (40–105) | 69 (47–102) | 0.979 | |
| Week 4 post-vaccine 2 | Seroconversion, n (%) | 39 (67%) | 22 (47%) | 38 (52%) | 0.080 |
| GM dilution (95% CI) | 49 (32–75) | 124 (61–249) | 88 (53–144) | 0.059 | |
GM, geometric mean. Calculated among seroconversion samples. Fisher's exact and one-way analysis of variance tests used to compare seroconversion rates and geometric means among responders, respectively. Missing values for binding antibody: 18–45 (week 2 post-vaccine 1, n = 2), 46–59 (week 2 post-vaccine 1, n = 1). Removed samples for binding antibody: 18–45 (vaccine 2, COVID infection n = 2). Missing values for binding and neutralising antibody: 18–45 (week 4 post-vaccine 2, n = 2), 46–59 (week 2 post-vaccine 2, n = 1; week 4 post-vaccine 2, n = 2), 60–75 (week 2 post-vaccine 2, n = 1; week 4 post-vaccine 2, n = 1). Removed samples for binding and neutralising antibody: 18–45 (week 2 post-vaccine 2, COVID infection n = 3; week 4 post-vaccine 2, COVID infection n = 3, authorised vaccine n = 1), 46–59 (week 4 post-vaccine 2, authorised vaccine n = 1). Significant value ≤0.05 is shown in bold.