Table 1.
Demographic and Clinical Characteristics of Participants Enrolled in the US Influenza Vaccine Effectiveness Network—United States, 2017–2018 Influenza Season
| Test Result Status | Vaccination Status | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Influenza Positive | Influenza Negative | Vaccinated | |||||||
| Characteristic | No. | (%) | No. | (%) | P Valuea | Total | No. | (%) | P Valueb |
| Overall | 3050 | … | 5386 | … | 8436 | 4113 | … | ||
| Study site | … | … | … | … | <.001 | … | … | … | <.001 |
| Michigan | 532 | (39) | 836 | (61) | 1368 | 750 | (55) | ||
| Pennsylvania | 501 | (38) | 804 | (62) | 1305 | 599 | (46) | ||
| Texas | 725 | (37) | 1260 | (63) | 1985 | 753 | (38) | ||
| Washington | 501 | (29) | 1224 | (71) | 1725 | 1022 | (59) | ||
| Wisconsin | 791 | (39) | 1262 | (61) | 2053 | 989 | (48) | ||
| Male sex | 1322 | (38) | 2131 | (62) | .001 | 3453 | 1553 | (45) | <.001 |
| Age group (y) | … | … | … | … | <.001 | … | … | … | <.001 |
| <5 | 262 | (24) | 847 | (76) | 1109 | 551 | (50) | ||
| 5–17 | 837 | (46) | 965 | (54) | 1802 | 632 | (35) | ||
| 18–49 | 965 | (34) | 1894 | (66) | 2859 | 1128 | (39) | ||
| 50–64 | 571 | (38) | 937 | (62) | 1508 | 891 | (59) | ||
| ≥65 | 415 | (36) | 743 | (64) | 1158 | 911 | (79) | ||
| Race/ethnicity | … | … | … | … | .02 | … | … | … | <.001 |
| White, non-Hispanic | 2171 | (36) | 3888 | (64) | 6059 | 3117 | (51) | ||
| Black, non-Hispanic | 266 | (40) | 392 | (60) | 658 | 226 | (34) | ||
| Other, non-Hispanic | 269 | (33) | 543 | (67) | 812 | 418 | (51) | ||
| Hispanic | 331 | (38) | 550 | (62) | 881 | 339 | (38) | ||
| Unknown | 13 | (50) | 13 | (50) | 26 | 13 | (50) | ||
| Any high-risk conditionc | 1370 | (34) | 2633 | (66) | .001 | 4003 | 2445 | (61) | <.001 |
| Asthma/pulmonary high-risk condition | 537 | (32) | 1125 | (68) | <.001 | 1662 | 994 | (60) | <.001 |
| Cardiovascular high-risk condition | 274 | (34) | 540 | (66) | .12 | 814 | 587 | (72) | <.001 |
| Diabetes high-risk condition | 232 | (34) | 449 | (66) | .24 | 681 | 480 | (70) | <.001 |
| Body mass index ≥40d | 179 | (32) | 381 | (68) | .03 | 560 | 360 | (64) | <.001 |
| Other high-risk condition | 922 | (35) | 1704 | (65) | .18 | 2626 | 1702 | (65) | <.001 |
| Interval from onset to enrollment (days) | … | … | … | … | <.001 | … | … | … | <.001 |
| <3 | 1444 | (45) | 1759 | (55) | 3203 | 1472 | (46) | ||
| 3–4 | 1066 | (35) | 2008 | (65) | 3074 | 1501 | (49) | ||
| 5–7 | 540 | (25) | 1619 | (75) | 2159 | 1140 | (53) | ||
| Influenza test resulte | |||||||||
| Negative | … | … | 5386 | … | 5386 | 2842 | (53) | ||
| Influenza B positive | 958 | …. | … | … | 958 | 377 | (39) | ||
| B/Victoria | 39 | … | … | … | 39 | 8 | (21) | ||
| B/Yamagata | 908 | … | … | … | 908 | 369 | (41) | ||
| Influenza A positive | 2103 | … | … | … | 2103 | 899 | (43) | ||
| A (H1N1)pdm09 | 318 | … | … | … | 318 | 93 | (29) | ||
| A (H3N2) | 1761 | … | … | … | 1761 | 795 | (45) |
a P value calculated using χ2 comparing frequency of participants testing influenza positive vs negative by characteristic.
b P value calculated using χ2 test that compares the frequency of vaccination by participant characteristic.
cPresence of a high-risk health condition is defined as the presence of ≥1 medical record–documented International Classification of Disease, 10 Edition, high risk code from 1 October 2016 to enrollment, as defined by the Advisory Committee on Immunization Practices guidance for conditions that increase risk for complications from influenza [26].
dBody mass index was calculated as kg/m2 from height and weight recorded in the electronic medical record. Calculated for adults aged ≥18 years only.
eFourteen influenza B viruses were of unknown lineage; 34 influenza A viruses were of unknown subtype. There were 25 coinfections that are each counted twice in the table above: 11 A(H3N2) and A(H1N1)pdm09, 9 B/Yamagata and A(H3N2), 3 B/Victoria and B/Yamagata, 1 A(H1N1)pdm09 and B/Yamagata, and 1 B/Yamagata and A of unknown subtype.