Table 1.
Characteristics of Study Participants by Prior Season Vaccination Status Among Enrollees ≥9 Years Old in the United States Flu Vaccine Effectiveness Network During 6 Seasons, 2012–2013 Through 2017–2018
| Without Prior Season Vaccination | With Prior Season Vaccination | ||||
|---|---|---|---|---|---|
| Characteristic | No. | (Row %) | No. | (Row %) | P Valuea |
| Total | 17 281 | (54) | 14 538 | (46) | |
| Site | <.001 | ||||
| Michigan | 2470 | (52) | 2282 | (48) | |
| Pennsylvania | 3742 | (63) | 2153 | (37) | |
| Texas | 4192 | (67) | 2100 | (33) | |
| Washington | 3641 | (44) | 4610 | (56) | |
| Wisconsin | 3236 | (49) | 3393 | (51) | |
| Age group, y | <.001 | ||||
| 9–17 | 3365 | (60) | 2206 | (40) | |
| 18–49 | 8903 | (66) | 4566 | (34) | |
| 50–64 | 3619 | (49) | 3782 | (51) | |
| ≥65 | 1394 | (26) | 3984 | (74) | |
| Sex | <.001 | ||||
| Male | 6996 | (58) | 5092 | (42) | |
| Female | 10 285 | (52) | 9446 | (48) | |
| Race/ethnicityb | <.001 | ||||
| White, non-Hispanic | 13 111 | (53) | 11 732 | (47) | |
| Black, non-Hispanic | 1354 | (65) | 727 | (35) | |
| Hispanic | 1293 | (53) | 1157 | (47) | |
| Other, non-Hispanic | 1480 | (63) | 884 | (37) | |
| Any high-risk medical conditionc | <.001 | ||||
| No | 11 092 | (65) | 5846 | (34) | |
| Yes | 6189 | (42) | 8692 | (58) | |
| Illness onset to specimen collection, interval | <.001 | ||||
| ≤2 d | 5771 | (58) | 4210 | (42) | |
| 3–4 d | 6873 | (55) | 5546 | (45) | |
| 5–7 d | 4637 | (49) | 4779 | (51) | |
| Seasond | <.001 | ||||
| 2012–2013 | 2825 | (60) | 1853 | (40) | |
| 2013–2014 | 2219 | (53) | 1961 | (47) | |
| 2014–2015 | 3187 | (49) | 3278 | (51) | |
| 2015–2016 | 2765 | (56) | 2185 | (44) | |
| 2016–2017 | 2841 | (54) | 2464 | (46) | |
| 2017–2018 | 3444 | (55) | 2797 | (45) | |
a P values were calculated with a χ 2 test.
bEighty-one participants were missing race/ethnicity.
cPresence of ≥1 documented high-risk code in prior year that may increase risk for complications attributable to severe influenza as defined by the Advisory Committee on Immunization Practices, including chronic pulmonary (including asthma); cardiovascular (excluding isolated hypertension); renal, hepatic, neurologic, hematologic, or metabolic disorders (including diabetes mellitus); or persons who are immunocompromised due to any cause (including but not limited to immunosuppression caused by medications or human immunodeficiency virus infection) [1].
dDistribution of participants by enrollment season.