| Study characteristics |
| Methods |
Case‐control study conducted in England, during the 1989 to 1990 influenza season, in the community. Data sources were: hospital and general practitioner records. Follow‐up period was 1 December 1989 to 31 January 1990. Cases were hospitalised and their discharge diagnosis or cause of death was pneumonia, influenza, emphysema, or bronchitis; community controls were matched for age and sex. Specific controls were matched for cases who died; controls died 6 to 12 months later. |
| Participants |
445 patients admitted to hospital (303 cases were identified; 156 cases and 289 controls were included in the analysis, respectively), 16 years of age or older |
| Interventions |
Parenteral influenza vaccine. Vaccine strains matched the circulating strain. |
| Outcomes |
Hospitalisation from pneumonia, influenza, emphysema, or bronchitis (ICD 466, 480.9 to 482.9, 485 to 492.8) |
| Notes |
2 exposure definitions were used: current vaccinees and previous vaccinees (vaccinated between 1985 and 1989): the first was used; pneumococcal vaccination was very unlikely; circulating strain was A/England/308/89. The season was an epidemic one. The study controls for confounders in analysis: health status, previous vaccination. Quantitative analysis was also performed. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
B ‐ Unclear |
