| Study characteristics |
| Methods |
Case‐control study conducted in Michigan, USA during the 1989 to 1990 influenza season, in the community. Data sources were: discharge diagnoses, mailed questionnaire. Follow‐up period was 1 November 1989 to 30 April 1990. Cases were admitted to the hospital with pneumonia or influenza; community controls were randomly selected. |
| Participants |
1907 non‐institutionalised people (1354 cases and 2389 controls were identified; 721 and 1786 were included in analysis, respectively), 65 years or older |
| Interventions |
Parenteral influenza vaccine; 35% of cases and 28% of controls received pneumococcal vaccination. Vaccine strains matched the circulating strain. |
| Outcomes |
Hospitalisation from pneumonia and influenza (ICD 480.8‐483, 484.7‐487.1) |
| Notes |
Circulating strain: A/Shanghai/11/87. The season was an epidemic one. The study controls for confounders in analysis: health status, flu activity, pneumococcal vaccination, smoke. Peak data were used. Quantitative analysis was also performed. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
B ‐ Unclear |
