Bueving 2003.

Methods	Randomisation took place by the manufacturer when packing vaccine and placebo, from a computer‐generated list Blinding: double‐blind with active or placebo vaccines used Number excluded: 696 children enrolled out of 3220 invited by general practitioners (GPs) Withdrawals: 3 lost diaries from vaccine group and 5 from placebo group Baseline characteristics: comparable
Participants	Location: Rotterdam, Netherlands, community‐based study Number and age of participants: 696 children aged 6 to 18 years; mean age 10.5 years (standard deviation 3.2) Asthma definition and severity: children selected from GP files based on prescribed asthma medication. Mean forced expiratory volume in 1 second (FEV1) 89% predicted and 16% had ever been hospitalised for asthma Inclusion criteria: maintenance therapy for asthma (inhaled corticosteroids or cromoglycate), or more than 52 doses of relief medication during the previous 12 months Exclusion criteria: other chronic diseases, allergy to chicken protein and insufficient understanding of the Dutch language
Interventions	Vaccination type: inactivated influenza vaccine intramuscular injection. The vaccine composition for 1999 to 2000 was a combination of A/Sydney/5/97 H3N2‐like, A/Beijing/262/95‐like and B/Beijing/184/93‐like strains and for 2000 to 2001 A/Moscow/10/99 H3N2‐like, A/New Caledonia/20/99 H1N1‐like and B/Beijing/184/93‐like strains as advised by the World Health Organization Placebo group: buffered phosphate solution with the same pH value and similar appearance as the inactivated influenza vaccine
Outcomes	Primary outcome: influenza‐related asthma exacerbations (number, duration and severity) Secondary outcomes: adverse effects of the vaccination including airway symptoms; the number, duration and severity of all asthma exacerbations; proportion of days with symptoms of upper respiratory tract (URTI), lower respiratory tract (LRT) or both; use of asthma medication and other medication; consultations of a specialist or GP; admittance to hospital for airway problems; rising of antibody‐titre against influenza and the number of serologically proven influenza infections
Notes	Power calculations suggested 600 patients needed to be enrolled
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated list
Allocation concealment (selection bias)	Low risk	Randomisation, packing and labelling took place by the manufacturer
Blinding of participants and personnel (performance bias) All outcomes	Low risk	All those involved, i.e. patients and parents, GPs and investigators, were blinded
Blinding of outcome assessment (detection bias) All outcomes	Low risk	All those involved, i.e. patients and parents, GPs and investigators, were blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	344/347 and 344/349 participants provided diary data