| Study characteristics |
| Methods |
Case‐control study conducted in the USA during the 1981 to 1989 period, in the community. Data source was a managed care organisation database. Follow‐up period was the epidemic period according to surveillance data. Cases were admitted to services with pneumonia or influenza or died in hospital from pneumonia or influenza; community controls were matched for high‐risk status. |
| Participants |
251,034 members of a medical care programme, 65 years or older |
| Interventions |
Parenteral influenza vaccine; participants also received pneumococcal vaccination. Vaccine strains matched the circulating strain. |
| Outcomes |
Pneumonia and influenza without hospitalisation, hospitalisation from pneumonia and influenza (ICD 480‐487), hospitalised death |
| Notes |
Most of the seasons were epidemic, and vaccine strains did not match the circulating strains. The study controls for confounders in analysis (age, sex, pneumococcal vaccination). Data are stratified by health status, but allow only quantitative analysis. The odds ratio adjusted by risk status was obtained by pooling the data reported in the paper using Wolf method. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Low risk |
A ‐ Adequate |
