| Methods |
Matched case‐control study |
| Participants |
Navajo adults with IPD aged 18 and over with medical risk factor or above 65 years |
| Interventions |
108 IPD case patients recruited in 1996 or 1997
330 control patients without prior IPD or pneumonia
23‐valent PPV |
| Outcomes |
B1. IPD
B2. Vaccine‐type IPD |
| Notes |
Matched 1: up to 7 according to age, sex, chronic medical condition (duration, number of conditions and severity)
Cases more likely to have underlying disease and multiple underlying disease conditions (P = 0.0002). Cases may have had prior IPD and controls excluded if prior IPD or pneumonia in previous 10 years
Likely bias against vaccine effectiveness
AIDS patients not excluded
Vaccinated defined as receiving any prior dose (23‐valent PPV) |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Random sequence generation (selection bias) |
High risk |
Non‐randomised study |
| Allocation concealment (selection bias) |
Low risk |
Study investigators determining participant inclusion unlikely to be aware of vaccination status |
| Confounding
All outcomes |
Low risk |
4/5 important confounding factors. Study did not control for smoking due to low prevalence |
| 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 clear whether there were withdrawals |
| Selective reporting (reporting bias) |
Low risk |
Limited extent to which analysis could have been manipulated to bias the findings |
