TABLE 1.
Characteristics of influenza A(H1N1)pdm09 (n = 253), A(H3N2) (n = 1595), and controls (n = 9626) included in the I‐MOVE primary care multicentre case control study, influenza season 2021–2022
| Variables | Number of influenza A(H1N1)pdm09 cases/total n(%) N = 253 | Number of influenza A(H3N2) cases/total n(%) N = 1595 | Number of test‐negative controls/total n(%) N = 9626 |
|---|---|---|---|
| Median age | 27 | 24 | 33 |
| Age groups | |||
| 0–4 | 55/253 (22) | 130/1595 (8) | 1784/9626 (19) |
| 5–14 | 53/253 (21) | 301/1595 (19) | 1212/9626 (13) |
| 15–64 | 136/253 (54) | 1002/1595 (63) | 5612/9626 (58) |
| ≥65 | 9/253 (4) | 162/1595 (10) | 1018/9626 (11) |
| Sex | |||
| Female | 125/253 (49) | 830/1595 (52) | 4713/9626 (49) |
| Days between onset of symptoms and swabbing | |||
| 0 | 13/253 (5) | 38/1595 (2) | 300/9626 (3) |
| 1 | 91/253 (36) | 259/1595 (16) | 1568/9626 (16) |
| 2 | 65/253 (26) | 830/1595 (52) | 5062/9626 (53) |
| 3 | 47/253 (19) | 231/1595 (14) | 1155/9626 (12) |
| 4–7 | 37/253 (15) | 237/1595 (15) | 1541/9626 (16) |
| Seasonal influenza vaccination, 2021–2022 | 7/253 (3) | 227/1595 (14) | 1731/9626 (18) |
| Current and previous season influenza vaccination status | |||
| Not vaccinated | 205/213 (96) | 980/1186 (83) | 5910/7619 (78) |
| Current season vaccination only | 0/213 (0) | 23/1186 (2) | 201/7619 (3) |
| Previous season vaccination only | 4/213 (2) | 55/1186 (5) | 496/7619 (7) |
| Current and previous season vaccination | 4/213 (2) | 128/1186 (11) | 1012/7619 (13) |
| Missing | 40 | 409 | 2007 |
| Seasonal vaccination types a | |||
| Quadrivalent vaccine b | 5 (100) | 80 (51) | 850 (64) |
| Adjuvanted vaccine | 0 (0) | 74 (47) | 395 (30) |
| High dose quadrivalent | 0 (0) | 0 (0) | 49 (4) |
| LAIV | 0 (0) | 2 (1) | 28 (2) |
| Quadrivalent cell‐based | 0 (0) | 1 (1) | 6 (<1) |
| Unknown | 2 | 70 | 403 |
| ≥1 chronic condition | 36/253 (14) | 358/1595 (22) | 2281/9626 (24) |
| Belongs to target group for vaccination | 41/253 (16) | 445/1595 (28) | 3090/9624 (32) |
| Missing | 0 | 0 | 2 |
| SARS‐CoV‐2 positive | 5/253 (2) | 41/1595 (3) | 2466/9625 (26) |
| Missing | 0 | 0 | 1 |
Abbreviation: LAIV, live attenuated influenza vaccine.
a
Among vaccinated.
b
Quadrivalent, normal dose, inactivated, non‐adjuvanted egg‐propagated.