TABLE 1. Selected characteristics of enrolled patients with medically attended acute respiratory illness and participants of a community cohort, by influenza test result and seasonal influenza vaccination status — Wisconsin, October 2022–February 2023.
| Characteristic | Test-negative case-control study* |
Community cohort study† |
|||||
|---|---|---|---|---|---|---|---|
| No. of participants | No. (%) |
No. of participants | No. (%) |
||||
| Vaccinated§ | Positive influenza test result | Negative influenza and SARS-CoV-2 test results | Vaccinated¶ | Positive influenza test result | |||
|
Total
|
545
|
186 (34)
|
116 (21)
|
429 (79)
|
241
|
94 (39)
|
34 (14)
|
|
Age group**
| |||||||
| 6 mos–17 yrs |
223 |
69 (31) |
42 (19) |
181 (81) |
241 |
94 (39) |
34 (14) |
| 18–64 yrs |
322 |
117 (36) |
74 (23) |
248 (77) |
NA |
NA |
NA |
|
Sex
| |||||||
| Female |
318 |
127 (40) |
65 (20) |
253 (80) |
116 |
49 (42) |
17 (15) |
| Male |
227 |
59 (26) |
51 (22) |
176 (78) |
125 |
45 (36) |
17 (14) |
|
Race and ethnicity
| |||||||
| Hispanic or Latino |
35 |
12 (34) |
6 (17) |
29 (83) |
2 |
2 (100) |
1 (50) |
| White, non-Hispanic |
482 |
161 (33) |
105 (22) |
377 (78) |
233 |
92 (39) |
33 (14) |
| Other races, non-Hispanic†† |
28 |
13 (46) |
5 (18) |
23 (82) |
6 |
0 (—) |
0 (—) |
|
Higher-risk conditions
§§
| |||||||
| Yes |
154 |
69 (45) |
30 (19) |
124 (81) |
31 |
13 (42) |
6 (19) |
| No |
391 |
117 (30) |
86 (22) |
305 (78) |
210 |
84 (39) |
28 (13) |
|
≥2 COVID-19 vaccine doses¶¶
| |||||||
| Yes |
258 |
133 (52) |
51 (20) |
207 (80) |
115 |
61 (53) |
20 (17) |
| No |
287 |
53 (18) |
65 (23) |
222 (77) |
126 |
33 (26) |
14 (11) |
|
Month of illness onset
| |||||||
| Nov–Dec 2022 |
227 |
75 (33) |
86 (38) |
141 (62) |
NA |
NA |
32 (94) |
| Jan–Feb 2023 |
318 |
111 (35) |
30 (9) |
288 (91) |
NA |
NA |
2 (6) |
|
Influenza test result
| |||||||
| Negative |
429 |
160 (37) |
NA |
429 (100) |
207*** |
88 (43) |
NA |
| Influenza A–positive |
116 |
26 (22) |
116 (100)††† |
NA |
34 |
6 (18) |
34 (100)††† |
| A(H3N2) |
86 |
16 (19) |
86 (74)††† |
NA |
29 |
5 (17) |
29 (85)††† |
| A(H1N1)pdm09 |
29 |
10 (34) |
29 (25)††† |
NA |
1 |
0 (—) |
1 (3)††† |
| A: unknown subtype | 1 | 0 (—) | 1 (1)††† | NA | 4 | 1 (25) | 4 (12)††† |
Abbreviations: ACIP = Advisory Committee on Immunization Practices; ccIIV4 = cell culture–based vaccine; MCHS = Marshfield Clinic Health System; NA = not applicable.
* A total of 109 participants received a positive test result for SARS-CoV-2 virus infection and were excluded. Participants with uncertain influenza vaccination status (12), with receipt of vaccine ≤13 days before illness (four), or who were aged <9 years and partially vaccinated (seven) were excluded from analysis.
† One child was partially vaccinated according to ACIP recommendations before the analysis period and was excluded.
§ Defined as receipt of any seasonal influenza vaccine according to ACIP recommendations ≥14 days before illness onset based on MCHS vaccination records. Most vaccinated participants (84%) received ccIIV4.
¶ Defined as receipt of seasonal influenza vaccine according to ACIP recommendations ≥14 days before influenza infection or before the end of follow-up based on MCHS vaccination records. Most vaccinated participants (84%) received ccIIV4.
** Age on the date of the clinical encounter for acute respiratory illness for the test-negative case-control study and as of September 1, 2022, for the community cohort study.
†† Includes persons who are American Indian or Alaska Native, Asian, Black or African American, Native Hawaiian or other Pacific Islander, and multiracial.
§§ Based on self-report of asthma or another chronic lung disease, cancer, diabetes, heart disease including high blood pressure, immunocompromising condition, kidney disease, liver disease, obesity, or pregnancy during the 12 months preceding the test-negative case-control study enrollment and self-report of asthma, immunocompromised state, serious heart condition, or other chronic lung disease for the community cohort study.
¶¶ Based on self-report for the test-negative case-control study and health records for the community cohort study.
*** Includes cohort participants with acute respiratory illness who received negative influenza test results, those with no reported acute respiratory illness, and three persons with influenza infections occurring within 14 days after vaccination who were excluded from the study at the time of vaccination.
††† Column percentages.