| Study characteristics |
| Methods |
Prospective cohort study conducted in Spain during the 1988 to 1989 influenza season, in the community. Data sources were the health centre register, death certificate archives, hospital records. Follow‐up period was 1 November 1988 to 30 May 1989. In the first of the 4 health centres, all elderly people were enrolled; in the others only people approaching the centre for health reasons were enrolled. |
| Participants |
4558 people enrolled at 4 health centres (1998 treated and 2560 controls, all included in the analysis), 65 years or older, mean age 74 years |
| Interventions |
Parenteral influenza vaccine. Vaccine strains matched the circulating strain. |
| Outcomes |
All hospitalisations and hospitalisation from cardio‐respiratory causes (ICD 401‐414 and 460‐519); deaths from all causes. Only deaths from all causes are included in analysis. |
| Notes |
The season was an epidemic one. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
B ‐ Unclear |
