Table 1.
Characteristics of the study participants.
| Variables | Cases (n = 799) |
Controls (n = 1196) | p-Value a |
|---|---|---|---|
| Male | 430 (54) | 652 (54) | 0.76 |
| Age (years) | |||
| Median (range) | 3 (1–5) | 2 (1–5) | <0.01 |
| Age (years) | |||
| 1 | 136 (17) | 371 (31) | |
| 2 | 143 (18) | 290 (24) | |
| 3 | 159 (20) | 213 (18) | |
| 4 | 191 (24) | 196 (16) | |
| 5 | 170 (21) | 126 (11) | <0.01 |
| Enrolment season | |||
| 2016/17 | 367 (46) | 627 (52) | |
| 2017/18 | 432 (54) | 569 (48) | <0.01 |
| Siblings (present) | 641 (80) | 835 (70) | <0.01 |
| Nursery school (yes) | 662 (83) | 896 (75) | <0.01 |
| Medical comorbidities b | 70 (9) | 130 (11) | 0.12 |
| Number of outpatient visits in last year | |||
| 0–4 | 471 (59) | 549 (46) | |
| 5–9 | 209 (26) | 367 (31) | |
| ≥10 | 119 (15) | 280 (23) | <0.01 |
| Influenza vaccination in prior season | 255 (32) | 434 (36) | 0.04 |
| Vaccinated until the season before the prior season (+) c | 281 (35) | 313 (26) | <0.01 |
| Influenza diagnosis in prior season (+) | 157 (20) | 175 (15) | <0.01 |
Data are expressed as n (%) unless otherwise indicated. a Chi-square test or Wilcoxon rank sum test was used as appropriate. b Respiratory/heart/renal/neurology/hematology/allergic/congenital diseases and immunosuppression state. c All children aged 1 year old were treated as never vaccinated until the season before the prior season in the analysis.