Table 2.
Seroprotection rate for chikungunya virus-specific neutralising antibodies on day 29
|
18–64 years (stratum A) |
≥65 years (stratum B) |
Total |
||||
|---|---|---|---|---|---|---|
| VLA1553 (n=207) | Placebo (n=73) | VLA1553 (n=59) | Placebo (n=23) | VLA1553 (n=266) | Placebo (n=96) | |
| Total* (n) | 207 | 73 | 59 | 23 | 266 | 96 |
| Participants with seroprotection, n (%) | 204 (98·6%) | 0 | 59 (100%) | 0 | 263 (98·9%) | 0 |
| 95% CI for seroprotection rate | 95·8–99·7 | 0·0–4·9 | 93·9–100·0 | 0·0–14·8 | 96·7–99·8 | 0·0–3·8 |
| p value† | <0·0001 | >0·9999 | <0·0001 | >0·9999 | <0·0001 | >0·9999 |
| Difference in seroprotection rate‡ | 98·6 | .. | 100·0 | .. | 98·9 | .. |
| 95% CI | 96·9–100·0 | .. | 100·0–100·0 | .. | 97·6–100·0 | .. |
| p value§ | <0·0001 | .. | <0·0001 | .. | <0·0001 | .. |
Data are in the per-protocol population. Percentages are based on the number of baseline negative participants with non-missing titres at the visit. Seroprotection was defined as μPRNT50 titre ≥150 for μPRNT baseline negative participants (<20). Two-sided 95% exact (Clopper-Pearson) CIs are presented. Where the upper bound of the CI would be greater than 100%, the upper confidence limit is restricted to 100. μPRNT50 titre=serum dilution with 50% plaque reduction in a micro plaque reduction neutralisation test.
Number of μPRNT baseline negative participants (<20) with non-missing titres on day 29.
p value from an exact binomial test for the null-hypothesis H0: seroprotection rate ≤70% against the alternative H1: seroprotection rate >70% with a one-sided significance level of 2·5%.
Differences, p values, and associated CIs are presented for the VLA1553 group minus the placebo group.
p value from Fisher's exact test.