| Study characteristics |
| Methods |
Prospective cohort study conducted in the USA during the 1997 to 1998 influenza season, in the community. Data source was a managed care organisation database. Follow‐up period was 23 November 1997 to 4 April 1998. |
| Participants |
158,454 members of a medical care programme continuously enrolled for the 1‐year period (92,001 treated and 66,453 controls, all included in the analysis), 65 years or older |
| Interventions |
Parenteral influenza vaccine. Vaccine did not match the circulating strain. |
| Outcomes |
Combined outcome: hospitalisation from influenza and pneumonia (ICD 480‐487) or death from all causes |
| Notes |
The study controls for confounders in analysis: age, gender, health status. Data were presented by health status. No information about pneumococcal vaccination. The season was an epidemic one; circulating strain: A/Sydney‐like. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
D ‐ Not used |
