| Methods |
Matched case‐control |
| Participants |
Immunocompetent older adults aged 55 years and above |
| Interventions |
Cases (n = 122) IPD cases from Jan 1980 to July 1986
Controls (n = 244) consecutive hospital admissions
Vaccine valency not specified |
| Outcomes |
B1. IPD (immunocompetent and immunocompetent elderly) |
| Notes |
Matched 2:1 according to hospital, admission date, comorbid conditions (number and severity)
Sample size based on vaccine efficacy at 50%, power 0.80, error 0.05 (one tailed) and 20% vaccination coverage in controls requires 164 cases and 328 controls
Controls excluded if they had radiographically proven pneumonia during the study period
Vaccinated definition (time since dose) not specified |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Random sequence generation (selection bias) |
High risk |
Non‐random study |
| Allocation concealment (selection bias) |
Low risk |
Study investigators determining participant inclusion unlikely to be aware of vaccination status |
| Confounding
All outcomes |
Low risk |
3/6 important confounding factors covered, however, critical factors covered |
| Blinding of participants and personnel (performance bias)
All outcomes |
Unclear risk |
NA |
| Blinding of outcome assessment (detection bias)
All outcomes |
Low risk |
Due to the specificity of outcome |
| Incomplete outcome data (attrition bias)
All outcomes |
Unclear risk |
Not described |
| Selective reporting (reporting bias) |
Low risk |
Limited extent to which analysis could have been manipulated to bias the findings |
