Table 1.
Characteristics of Influenza A(H3N2) Cases and Influenza-Negative Controls, US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN), 2018–2019 (n = 2304)
| Characteristic | Influenza A(H3N2) Cases | Influenza-Negative Controls | P Valuea | Standardized Differenceb |
|---|---|---|---|---|
| No. | 247 | 2057 | ||
| Site | <.001 | 0.33 | ||
| Central Texas | 59 (23.9) | 716 (34.8) | ||
| Southeast Michigan | 56 (22.7) | 472 (22.9) | ||
| Western Pennsylvania | 60 (24.3) | 521 (25.3) | ||
| Central Tennessee | 72 (29.1) | 348 (16.9) | ||
| Baseline characteristics | ||||
| Demographics and behavioral risk factors | ||||
| Age groupc | .012 | 0.20 | ||
| 18 to ≤56 y | 66 (27) | 705 (34) | ||
| >56 to ≤69 y | 80 (32) | 689 (34) | ||
| >69 y | 101 (41) | 663 (32) | ||
| Age, y, mean (SD) | 63.47 (17.95) | 61.31 (16.64) | .056 | 0.13 |
| Female sex | 138 (55.9) | 1158 (56.3) | .953 | 0.01 |
| Black race | 60 (24.3) | 538 (26.2) | .579 | 0.04 |
| Community dwelling | 231 (93.5) | 1943 (94.5) | .648 | 0.04 |
| Insured | 237 (96.0) | 1940 (94.3) | .358 | 0.08 |
| Current tobacco smoking | 50 (20.2) | 557 (27.1) | .026 | 0.16 |
| Current vaping/e-cigarette use | 7 (2.8) | 105 (5.1) | .158 | 0.12 |
| Comorbid health conditionsd | ||||
| Obstructive lung disease | 92 (37.2) | 1038 (50.5) | <.001 | 0.27 |
| Nonobstructive lung disease | 68 (27.5) | 895 (43.5) | <.001 | 0.34 |
| Heart disease | 134 (54.3) | 1280 (62.2) | .018 | 0.16 |
| Congestive heart failure | 53 (21.5) | 666 (32.4) | .001 | 0.25 |
| Neurologic disorder | 71 (28.7) | 710 (34.5) | .082 | 0.12 |
| Renal disorders | 90 (36.4) | 852 (41.4) | .151 | 0.10 |
| Malignancy | 57 (23.1) | 482 (23.4) | .964 | 0.01 |
| Hematologic disorders | 24 (9.7) | 230 (11.2) | .557 | 0.05 |
| Metabolic disorders | 133 (53.8) | 1187 (57.7) | .275 | 0.08 |
| Diabetes/obesity/endocrine disorders | 169 (68.4) | 1530 (74.4) | .05 | 0.13 |
| Health status indicators | ||||
| No. of ACIP high-risk conditions, mean (SD) | 4.59 (3.22) | 5.42 (3.27) | <.001 | 0.26 |
| Charlson Comorbidity Index, mean (SD) | 2.61 (3.00) | 3.09 (3.00) | .018 | 0.16 |
| Frailty score (0–5), mean (SD) | 1.72 (1.50) | 2.01 (1.46) | .003 | 0.20 |
| Home oxygen use | 56 (23.0) | 565 (27.6) | .139 | 0.11 |
| ≥1 hospitalization in prior year (self-report) | 119 (48.2) | 1309 (63.6) | <.001 | 0.32 |
| Self-reported chemotherapy/radiation, immunosuppressive medications | 80 (32.4) | 823 (40.0) | .024 | 0.16 |
| Immunosuppression by ICD-10 code and/or self-report | 103 (41.7) | 1045 (50.8) | .008 | 0.18 |
| Influenza vaccination habite | ||||
| Never/rarely | 38 (15.4) | 452 (22.0) | .004 | 0.24 |
| Sometimes | 9 (3.6) | 140 (6.8) | ||
| Always/almost always | 200 (81.0) | 1465 (71.2) | ||
| Vaccination habit score (0–2), mean (SD) | 1.66 (0.73) | 1.49 (0.83) | .003 | 0.21 |
| Influenza vaccination status | ||||
| Vaccinated by documentation or plausible self-reportf | 194 (78.5) | 1455 (70.7) | .010 | 0.18 |
| Vaccinated by self-reportg | 190 (76.9) | 1426 (69.3) | .014 | 0.17 |
| Admission characteristics | ||||
| Days from illness onset to admission, mean (SD) | 2.78 (2.15) | 2.86 (2.37) | .582 | 0.04 |
| Admitted to tertiary care hospital | 118 (47.8) | 1141 (55.5) | .026 | 0.15 |
| Presented with influenza-like illnessh | 152 (61.5) | 823 (40.0) | <.001 | 0.44 |
| Admitted to intensive care unit | 20 (8.1) | 248 (12.1) | .082 | 0.13 |
| Length of hospital stay, d, mean (SD) | 3.97 (3.46) | 4.91 (4.60) | .002 | 0.23 |
| Died in hospital | 2 (0.8) | 25 (1.2) | .805 | 0.04 |
Data are presented as No. (%) unless otherwise indicated.
Abbreviations: ACIP, Advisory Committee on Immunization Practices; ICD-10, International Classification of Diseases, 10th Edition; SD, standard deviation.
a P value for test of difference across case and control groups based on χ 2 statistic for categorical variables,
t test for difference of means of normally distributed continuous variables, and nonparametric log-rank test for nonnormally distributed continuous variables.
bStandardized absolute mean differences >0.10 shown in bold; standardized differences ≤0.10 are generally considered negligible differences between groups.
cAge groups defined by tertile of age distribution of all subjects.
dDerived from ICD-10 codes associated with inpatient and outpatient medical encounters in the year prior to enrollment admission.
eDefined by patient self-report during enrollment interview.
fPlausible self-report defined as affirmative self-report of current season vaccination including known or approximate date and location of vaccination.
gSelf-report defined as affirmative self-report of current season vaccination including known or approximate date.
hInfluenza-like illness defined as self-reported subjective fever/feverishness plus cough or sore throat.