| Study characteristics |
| Methods |
Prospective cohort study conducted in the USA, during the 1998 to 1999 influenza season, in the community. Data source was the managed care organisation database. Follow‐up period was 15 November to 31 February. The rate was adjusted for age, sex, health status. |
| Participants |
140,055 members of a medical care programme continuously enrolled for the 1‐year period (77,738 treated and 62,317 controls, all included in the analysis), 65 years or older |
| Interventions |
Parenteral influenza vaccine. Vaccine strains matched the circulating strain. |
| Outcomes |
Hospitalisation from pneumonia and influenza (ICD 480‐487), hospitalisation from cerebrovascular disease (ICD 431‐437), hospitalisation from heart disease (ICD 410‐414, 428), death from all causes |
| Notes |
The season probably was an epidemic one. Quantitative analysis was also performed. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
B ‐ Unclear |
