Table 1. Characteristics of Influenza Cases Matched to Healthy Controls.
| Characteristic | Cases | Controls | Crude odds ratio |
| n (%) | n (%) | (95% CI) | |
| Sex | |||
| Male | 410 (71.8) | 1766 (77.3) | 0.74 (0.60–0.91) |
| Female | 161 (28.2) | 518 (22.7) | Ref |
| Age group | |||
| <25 | 175 (30.6) | 621 (27.2) | Ref |
| 25–29 | 153 (26.8) | 545 (23.9) | 0.99 (0.77–1.26) |
| 30–39 | 184 (32.2) | 725 (31.7) | 0.89 (0.70–1.12) |
| 40+ | 59 (10.3) | 393 (17.2) | 0.51 (0.37–0.72) |
| Race-ethnicity | |||
| White | 338 (59.2) | 1439 (63.0) | Ref |
| Black | 105 (18.4) | 439 (19.2) | 1.01 (0.79–1.30) |
| Hispanic | 56 (9.8) | 215 (9.4) | 1.11 (0.81–1.53) |
| Asian/Pacific Islander | 31 (5.4) | 93 (4.1) | 1.45 (0.94–2.23) |
| American Indian/Alaskan Native | 6 (1.0) | 30 (1.3) | 0.84 (0.35–2.04) |
| Other/unknown | 35 (6.1) | 68 (3.0) | 2.21 (1.44–3.39) |
| Service | |||
| Army | 232 (40.6) | 943 (41.3) | Ref |
| Air Force | 267 (46.8) | 1063 (46.5) | 1.16 (0.74–1.80) |
| Marine Corps | 17 (3.0) | 93 (4.1) | 0.61 (0.27–1.39) |
| Navy | 49 (8.6) | 165 (7.2) | 1.46 (0.84–2.55) |
| Coast Guard | 6 (1.0) | 20 (0.9) | 1.46 (0.46–4.68) |
| Number of prior vaccinations | |||
| 0 | 66 (11.6) | 84 (3.7) | Ref |
| 1+ | 505 (88.4) | 2200 (96.3) | 0.24 (0.16–0.35) |
Bolded cells indicate statistical significance.