| Methods |
Randomisation: stratified by 4 morbidity categories
Blinding: double‐blind
Exclusions: those in high‐risk groups (however, 25 asthmatic patients were included in the study)
Withdrawals: 0 but 1 patient in the placebo group had incomplete data
Baseline characteristics: no data |
| Participants |
Location: Netherlands
Patients were all aged 60 years or over. Of the 1838 patients participating in the study 25 had asthma (no details of definition or severity but severe cases likely to have been excluded). Of these, 14 received vaccine and 11 received placebo
Exclusion criteria: age under 60 years, living in old peoples' care homes or nursing homes, belonging to a high‐risk group (interpreted differently by general practitioners) |
| Interventions |
Vaccination type: purified split vaccine H1N1, H3N2, B45/90, B1/87 given intramuscularly
Placebo: physiological saline intramuscularly |
| Outcomes |
Early: adverse reactions (recalled by the patients after 4 weeks)
Late: serologically confirmed influenza |
| Notes |
No serologically confirmed influenza was seen in either the immunised or the placebo group |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Random sequence generation (selection bias) |
Low risk |
Stratified randomisation scheme |
| Allocation concealment (selection bias) |
Low risk |
Next consecutive numbered syringe used |
| Blinding of participants and personnel (performance bias)
All outcomes |
Unclear risk |
Saline placebo but no further details |
| Blinding of outcome assessment (detection bias)
All outcomes |
Low risk |
Questionnaires analysed by researchers blind to vaccination status |
| Incomplete outcome data (attrition bias)
All outcomes |
Low risk |
1791/1838 completed |
