Table 2.
Percentage of Subjects With HI Titers ≥1:40 at Day 1 and Day 43, GMRs Day 43/Day 1, and Percentages of Subjects Achieving Seroconversion or Significant Increases in HI Titers at Day 43
| Adult Subjects | Elderly Subjects | |||
|---|---|---|---|---|
| (Age 18–64 y, n = 891) | (Age ≥65 y, n = 1337) | |||
| Full-Dose | Half-Dose | Full-Dose | Half-Dose | |
| (n = 451) | (n = 440) | (n = 673) | (n = 664) | |
| Day 1: HI titers ≥1:40 (97.5% CI), % | 4.0 (2.0–7.0) | 4.0 (2.0–6.0) | 12 (10–15) | 10 (8.0–13) |
| Day 43: HI titers ≥1:40 (97.5% CI), % | 85 (81–88)a,b | 63 (58–68) | 81 (77–84)a,b | 63 (58–67) |
| Day 43/day 1: GMRs (95% CI),c | 41 (34–49)b | 11 (8.7–13)b | 16 (14–18)b | 5.7 (5.0–6.6)b |
| Day 43: Positivity conversion (97.5% CI), % | 83 (78–87) | 61 (55–67) | 76 (71–80) | 56 (51–61) |
| Day 43: Significant increase (97.5% CI), % | 83 (69–92) | 61 (43–77) | 66 (57–74) | 38 (29–47) |
| Day 43: Seroconversion (97.5% CI), % | 83 (78–87)a,b | 61 (56–66)a,b | 74 (70–77)a,b | 52 (48–56)a,b |
Abbreviations: CI, confidence interval; GMR, geometric mean ratio; HI, hemagglutination inhibition; seroconversion, defined as positivity or significant increase.
aOutcome met CBER criterion [16] for age group.
bOutcome met CHMP criterion [17] for age group.
cGMR was a secondary end point in the adult study and was not adjusted for multiplicity; therefore, GMR (97.5% CI) data are not available. Positivity conversion was defined as postvaccination HI titer ≥1:40 for subjects negative (titer < 1:10) at baseline or a minimum 4-fold increase in HI titer for subjects seropositive (titer ≥ 1:10) at baseline; significant increase in antibody titer was defined as a minimum 4-fold increase in HI titer for subjects seropositive (titer ≥ 1:10) at baseline.