| Study characteristics |
| Methods |
Case‐control study conducted in Michigan, USA during the 1991 to 1992 influenza season, in the community. Data sources were: database discharge diagnoses, mailed questionnaire. Follow‐up period was 1 November 1991 to 30 April 1992. Cases were people discharged from hospital with pneumonia or influenza; community controls were matched for age, sex, and residence. |
| Participants |
2761 non‐institutionalised elderly (1186 cases and 2345 controls were identified; 890 and 1871 were included in analysis, respectively), 65 years or older |
| Interventions |
Parenteral influenza vaccine, participants were also offered pneumococcal vaccine. Vaccine strains matched the circulating strain. |
| Outcomes |
Hospitalisation from pneumonia and influenza (ICD 480‐487) |
| Notes |
44% of cases and 32% of controls received pneumococcal vaccination. The season was probably an epidemic one. The study controls for confounders in analysis: influenza activity, health status, age, sex, region. Quantitative analysis was also performed. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
B ‐ Unclear |
