Note: The risk of bias by domain corresponds to the highest risk of bias among outcomes by domain.
The overall risk of bias corresponds to the overall highest risk of bias assessed among outcomes.
| Bias | Author's judgement | Support for judgement |
| Confounding |
Moderate |
The analysis was adjusted for age, geographic region, calendar time and local virus circulation, and weighted for inverse propensity to be vaccinated or unvaccinated using facility characteristics, sociodemographics, and underlying medical conditions. There is potential for uncontrolled confounding, given the observational nature of the data. |
| Selection of participants into the study |
Moderate |
The study used a test-negative design. This has the potential to suffer from selection bias by being restricted to individuals getting a test, although the issues are not yet well understood. |
| Clasification of interventions |
Low |
No concerns in this domain - vaccination status adequately measured. |
| Deviations from intervention |
Low |
No concerns in this domain - the study was observational. |
| Missing outcome data |
Low |
No concerns in this domain - data are available for all participants. |
| Measurement of the outcome |
Moderate |
There is potential risk of bias arising from the testing being influenced by knowledge of vaccination status in patients admitted to hospital and not being tested prior to hospitalization. |
| Selection of the reported results |
Moderate |
There is no evidence of a protocol specific to this study, and it is not clear whether the protocol for other VISION Network study (Thompson 2011) is applicable. |
| Overall risk of bias |
Moderate |
|
| Overall comment | The published report was used in data extraction and risk of bias assessment.
Some concerns over the possibility of uncontrolled confounding given the observational nature of the data, on outcome ascertainement being influenced by knowledge of vaccination status and on pre-specified plan not being available. |