| Study characteristics |
| Methods |
Prospective cohort study conducted in the USA during the 1997 to 1998 influenza season, in the community. Data source was the 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 |
Hospitalisation from influenza and pneumonia (ICD 480‐487), death from all causes |
| Notes |
Identical to Hak 2. Odds ratios adjusted for age, sex, site, health status were presented. Frequencies data were not available. To perform quantitative analysis adjusted data were used |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Low risk |
A ‐ Adequate |
