Baseline characteristics of the study population
| Vaccine | Placebo | |
| At inclusion visits n | 347 | 349 |
| Age yrs | 10.5±3.2 | 10.6±3.3 |
| Females % | 48.1 | 43.6 |
| Age of onset of asthma yrs | 3.5±3.8 | 3.3±3.4 |
| Ever vaccinated for influenza % | 53.6 | 56.7 |
| History of allergy % | 73.5 | 66.1 |
| Child born in the Netherlands % | 97.7 | 98.9 |
| FEV1 % predicted | 89.5±16.1 | 88.9±16.0 |
| At baseline visits | ||
| Quality of life¶ n | 331 | 331 |
| Total score | 6.16 | 6.16 |
| Activities | 5.60 | 5.60 |
| Emotions | 6.63 | 6.63 |
| Symptoms | 6.05 | 6.05 |
| Spirometry n | 332 | 337 |
| FEV1 | ||
| Mean | 2.13±0.76 | 2.13±0.80 |
| % predicted | 93±14 | 92±13 |
| FVC | ||
| Mean | 2.43±0.88 | 2.43±0.96 |
| % predicted | 92±14 | 90±14 |
| MEF50 | ||
| Mean | 2.68±1.10 | 2.66±1.0 |
| % predicted | 90±25 | 90±24 |
| MEF25 | ||
| Mean | 1.42±0.71 | 1.42±0.67 |
| % predicted | 94±36 | 96±36 |
Data are presented as mean±sd unless otherwise stated. FEV1: forced expiratory volume in one second; FVC: forced vital capacity; MEF50: Maximum expiratory flow at 50% FVC; MEF25: maximum expiratory flow at 25% of FVC. ¶: mean of scores ranging from 1–7, with higher scores indicating better quality of life.