Table 2.
Subject Demographics at Baseline
| Characteristic | aIIV3 (n = 936 508) |
IIV4e (n = 651 034) |
HD-IIV3 (n = 1 813 819) |
SMD aIIV3 vs IIV4e |
SMD aIIV3 vs HD-IIV3 |
|---|---|---|---|---|---|
| Mean age ± SD, y | 75.0 ± 6.7 | 74.2 ± 7.1 | 75.2 ± 6.9 | 0.05 | –0.02 |
| ≥65–≤74 y, No. (%) | 489 964 (52.3) | 372 868 (57.3) | 941 558 (51.9) | ||
| ≥75–≤84 y, No. (%) | 330 701 (35.3) | 197 129 (30.3) | 626 502 (34.5) | ||
| ≥85 y, No. (%) | 115 843 (12.4) | 81 037 (12.4) | 245 759 (13.5) | ||
| Female sex, No. (%) | 547 251 (58.4) | 381 138 (58.5) | 1 054 163 (58.1) | 0.00 | 0.00 |
| Race and ethnicity, No. (%) | |||||
| Black or African American | 35 506 (3.8) | 36 969 (5.7) | 86 709 (4.8) | –0.01 | –0.01 |
| White | 567 270 (60.6) | 337 374 (51.8) | 1 085 710 (59.9) | 0.03 | –0.01 |
| Other | 27 356 (2.9) | 49 050 (7.5) | 69 601 (3.8) | –0.02 | –0.02 |
| Not reported | 306 376 (32.7) | 227 641 (35.0) | 571 799 (31.5) | –0.01 | 0.03 |
| Hispanic | 32 336 (3.5) | 44 582 (6.8) | 59 507 (3.3) | –0.02 | 0.00 |
| Non-Hispanic | 795 072 (84.9) | 562 204 (86.4) | 1 534 000 (84.6) | ||
| Not reported | 109 100 (11.6) | 44 248 (6.8) | 220 312 (12.1) | ||
| Geographic region, No. (%) | |||||
| Northeast | 157 186 (16.8) | 143 583 (22.1) | 378 938 (20.9) | –0.02 | 0.00 |
| Midwest | 147 719 (15.8) | 116 805 (17.9) | 412 178 (22.7) | –0.01 | 0.00 |
| South | 526 419 (56.2) | 237 428 (36.5) | 645 854 (35.6) | 0.06 | 0.07 |
| West | 103 519 (11.1) | 150 226 (23.1) | 374 108 (20.6) | –0.03 | –0.08 |
| Other | 1665 (0.2) | 2992 (0.5) | 2741 (0.2) | 0.00 | 0.01 |
| Charlson comorbidity index ± SD | 1.4 ± 1.8 | 1.7 ± 2.0 | 1.6 ± 1.9 | –0.04 | –0.07 |
| Frailty index,a mean ± SD | 0.09 ± 0.09 | 0.10 ± 0.12 | 0.10 ± 0.11 | –0.04 | –0.05 |
| <5%, No. (%) | 274 365 (29.3) | 209 392 (32.2) | 553 025 (30.5) | 0.01 | –0.02 |
| ≥5%–<20%, No. (%) | 596 195 (63.7) | 375 066 (57.6) | 1 100 748 (60.7) | ||
| ≥20%, No. (%) | 65 948 (7.0) | 66 576 (10.2) | 160 046 (8.8) | ||
| Outpatient visits, mean ± SD | 1.0 ± 2.3 | 1.7 ± 3.2 | 1.7 ± 3.1 | –0.08 | –0.28 |
| All-cause hospitalizations, No. (%) | |||||
| 0 | 692 124 (73.9) | 427 514 (65.7) | 1 235 213 (68.1) | –0.04 | –0.06 |
| 1 | 153 869 (16.4) | 125 311 (19.2) | 333 474 (18.4) | ||
| ≥2 | 90 515 (9.7) | 98 209 (15.1) | 245 132 (13.5) | ||
| Place of service (data source), No. (%) | |||||
| Pharmacy-only claims | 672 751 (71.8) | 101 203 (15.5) | 586 152 (32.3) | ||
| Medical claims | 221 589 (23.7) | 449 819 (69.1) | 988 481 (54.5) | ||
| EMR-only claims | 42 168 (4.5) | 100 012 (15.4) | 239 186 (13.2) | ||
| No. recorded immunizations | |||||
| August 2019 | 63 579 (6.8) | 15 004 (2.3) | 17 416 (1.0) | ||
| September 2019 | 262 942 (28.1) | 153 998 (23.7) | 457 618 (25.2) | ||
| October 2019 | 423 696 (45.2) | 322 338 (49.5) | 829 140 (45.7) | ||
| November 2019 | 131 012 (14.0) | 96 013 (14.7) | 328 815 (18.1) | ||
| December 2019 | 40 248 (4.3) | 38 250 (5.9) | 123 955 (6.8) | ||
| January 2020 | 15 031 (1.6) | 25 431 (3.9) | 56 875 (3.1) | ||
Abbreviations: ADL, activities of daily living; eIIV3, egg-derived inactivated quadrivalent influenza vaccine; EMR, electronic medical record; SMD, standardized mean difference.
Frailty was approximated using a summary score for ADL [
] to represent an operational definition of frailty in claims data using ADL dependency as a proxy outcome (Supplementary Table 3).