Table 3.
Antibody Responses Prior to Vaccination and at 1 Month Postvaccination, by Vaccine Arm
| Virus | Intramuscular Vaccine (n = 200) | Intradermal Vaccine (n = 200) | P Value | ||
|---|---|---|---|---|---|
| Day 0 | Day 30 | Day 0 | Day 30 | ||
| Influenza A(H1N1) | |||||
| Seroprotection, No. (%; 95% CI) | 23 (12; 7–16) | 120 (60; 53–67) | 22 (11; 7–16) | 113 (57; 49–63) | .5 |
| Seroconversion, No. (%; 95% CI) | … | 97 (49; 41–56) | … | 94 (47; 40–54) | .8 |
| Geometric mean titer (range) | 10 (9–11) | 43 (36–52) | 10 (9–12) | 40 (33–49) | .7 |
| Geometric mean titer ratio (range) | … | 4 (4–5) | … | 4 (3–5) | .6 |
| Influenza A(H3N2) | |||||
| Seroprotection, No. (%; 95% CI) | 17 (9; 5–13) | 88 (44; 37–51) | 11 (6; 3–10) | 92 (46; 39–53) | .7 |
| Seroconversion, No. (%; 95% CI) | … | 68 (34; 27–41) | … | 83 (42; 35–49) | .1 |
| Geometric mean titer (range) | 7 (7–8) | 25 (21–30) | 7 (6–8) | 27 (22–33) | .5 |
| Geometric mean titer ratio (range) | … | 3 (3–4) | … | 4 (3–4) | .5 |
| Influenza B | |||||
| Seroprotection, No. (%; 95% CI) | 7 (4; 1–7) | 83 (42; 35–49) | 7 (4; 1–7) | 89 (45; 37–52) | .5 |
| Seroconversion, No. (%; 95% CI) | … | 73 (37; 30–44) | … | 72 (36; 29–43) | .9 |
| Geometric mean titer (range) | 7 (6–7) | 24 (20–28) | 8 (7–9) | 24 (20–28) | .9 |
| Geometric mean titer ratio (range) | … | 3 (3–4) | … | 3 (3–4) | .3 |
| All 3 influenza virus strains | |||||
| Seroprotection, No. (%; 95% CI) | 0 | 39 (20; 14–26) | 0 | 43 (22; 16–28) | .6 |
| Seroconversion, No. (%; 95% CI) | … | 30 (15; 10–21) | … | 28 (14; 10–20) | .8 |
| At least 1 of the 3 virus strains | |||||
| Seroprotection, No. (%; 95% CI) | 43 (22; 16–28) | 153 (77; 70–82) | 37 (19; 13–25) | 148 (74; 67–80) | .6 |
| Seroconversion, No. (%; 95% CI) | … | 135 (68; 61–74) | … | 138 (69; 62–75) | .7 |
Abbreviation: CI, confidence interval.