| Study characteristics |
| Methods |
Experimental study conducted in the Netherlands during the 1991 to 1992 influenza season, in the community. Follow‐up period was 1 November 1991 to 30 April 1992. Randomised, double‐blind, placebo controlled; randomisation scheme was stratified according to health status. |
| Participants |
1838 people not known as belonging to a high‐risk group (927 treated and 911 controls; 25 and 22 dropped out, respectively), 60 years or older |
| Interventions |
Parenteral influenza recommended vaccine: A/Singapore/6/86; A/Beijing/357/89; B/Beijing/1/97; B/Panama/45/90. Vaccine strains matched the circulating strains. |
| Outcomes |
Clinically defined ILI; laboratory‐confirmed ILI. Several definitions for clinical and laboratory ILI were tested; the Dutch Sentinel Stations definition is used (fever 37.8 °C or greater + cough or coryza or sore throat or headache or myalgia). |
| Notes |
The study year was an epidemic one; data were stratified by health status. Intention‐to‐treat analysis was performed. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Random sequence generation (selection bias) |
Low risk |
Adequate description |
| Allocation concealment (selection bias) |
Low risk |
Adequate description |
| Blinding (performance bias and detection bias)
All outcomes |
Low risk |
Adequate description |
| Incomplete outcome data (attrition bias)
All outcomes |
Low risk |
Adequate description |
