Table 1.
Baseline characteristics by vaccination with trivalent/quadrivalent standard dose influenza vaccine (SD-IIV3/4) or trivalent high dose influenza vaccine (HD-IIV3)
| Vaccination Status | |||
|---|---|---|---|
| Characteristics | Unvaccinated N=868 | SD-IIV3/4 n=1,420 | HD-IIV3 n=1,573 |
| Age on Sept.1, years, mean (SD) | 71.8 (6.3) | 73.3 (7) | 73.6 (6.9) |
| Female sex, n (%) | 535 (61.6) | 872 (61.4) | 980 (62.3) |
| Race, n (%) | |||
| White, non-Hispanic | 730 (84.6) | 1272 (90.1) | 1332 (84.9) |
| Black, non-Hispanic | 47 (3.9) | 36 (2.6) | 69 (4.4) |
| Other race, non-Hispanic | 52 (6.0) | 54 (3.8) | 130 (8.3) |
| Hispanic, any race | 34 (3.9) | 49 (3.5) | 37 (2.4) |
| Non-Smoker, n (%), ref.=ever smoked | 563 (91.8) | 1353 (95.0) | 1514 (96.7) |
| Season, n (%) | |||
| 2015–2016 | 186 (21.4) | 339 (23.9) | 260 (16.5) |
| 2016–2017 | 215 (24.8) | 308 (21.7) | 376 (23.9) |
| 2017–2018 | 214 (24.6) | 363 (25.6) | 387 (24.6) |
| 2018–2019 | 253 (29.2) | 410 (28.6) | 550 (35.0) |
| Site, n (%) | |||
| Michigan | |||
| 2015–2016 | 13 (11.5) | 30 (21.4) | 30 (10.2) |
| 2016–2017 | 24 (21.2) | 27 (19.3) | 44 (14.9) |
| 2017–2018 | 31 (27.4) | 31 (22.1) | 80 (27.1) |
| 2018–2019 | 45 (39.8) | 52 (37.2) | 141 (47.8) |
| Pennsylvania | |||
| 2015–2016 | 40 (24.8) | 46 (21.5) | 38 (21.2) |
| 2016–2017 | 35 (21.7) | 35 (16.4) | 59 (33.0) |
| 2017–2018 | 40 (24.8) | 30 (14.0) | 62 (34.6) |
| 2018–2019 | 46 (28.6) | 103 (48.1) | 20 (11.2) |
| Texas | |||
| 2015–2016 | 30 (15.7) | 62 (25.5) | 20 (18.4) |
| 2016–2017 | 45 (23.6) | 62 (25.5) | 26 (23.8) |
| 2017–2018 | 51 (26.7) | 82 (33.8) | 16 (14.7) |
| 2018–2019 | 65 (34.0) | 37 (15.2) | 47 (43.1) |
| Washington | |||
| 2015–2016 | 67 (30.7) | 88 (32.7) | 165 (18.4) |
| 2016–2017 | 52 (23.9) | 47 (17.5) | 235 (26.2) |
| 2017–2018 | 36 (16.5) | 53 (19.7) | 202 (22.5) |
| 2018–2019 | 63 (28.9) | 81 (30.1) | 295 (32.9) |
| Wisconsin | |||
| 2015–2016 | 36 (19.5) | 113 (20.4) | 7 (7.5) |
| 2016–2017 | 59 (31.9) | 137 (24.7) | 12 (12.9) |
| 2017–2018 | 56 (30.3) | 167 (30.2) | 27 (29.0) |
| 2018–2019 | 34 (18.4) | 137 (24.7) | 47 (50.6) |
| Interval from onset to enrollment, n (%) | |||
| 0–2 days | 212 (24.4) | 377 (26.6) | 328 (20.9) |
| 3–4 days | 316 (36.4) | 530 (37.3) | 568 (36.1) |
| 5–7 days | 340 (39.2) | 513 (36.1) | 677 (43.1) |
| One or more high-risk condition, n (%) | 672 (77.4) | 1250 (88.0) | 1371 (87.2) |
| Received previous year’s influenza vaccine, n (%) | 240 (27.6) | 1147 (80.8) | 1395 (88.7) |
| Hospitalized within last year, n (%)2 | 641 (77.0) | 1157 (88.5) | 1368 (87.4) |
| Hospitalization within 30 days after enrollment, n (%) | 31 (3.6) | 56 (3.9) | 34 (2.2) |
| Outpatient visits within last year, mean (SD) 3 | 3.9 (5.6) | 5.5 (6.6) | 6.0 (7.0) |
| High-risk conditions, mean (SD) | 2.3 (2.0) | 2.9 (2.0) | 2.8 (2.0) |
| Days from vaccination to enrollment | --- | 114 (43.1) | 120 (41.3) |
| Timing of vaccination (weeks), mean (SD) 4 | --- | 16.2 (4.1) | 13.0 (3.1) |
1
P value is for the comparison of SD-IIV3/4 and HD-IIV3
2
Prior health care utilization
3
Any outpatient medical encounter in past 12 months based on high risk codes
4
Timing of vaccination: week in the season when vaccinated beginning July 1.