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 estimate used a combination of a hazard ratio for hospitalization among test-positive cases and an odds ratio for testing positive from a test-negative case control study. The odds ratio was adjusted for age, sex, socioeconomic status (IMD quintiles), ethnicity, geographic location, specific populations (care home residents, healthcare workers), comorbidities (being in a vulnerable group) and calendar time, and additionally for recent travel. The hazard ratio was adjusted for age, time, being in a vulnerable group and ethnicity only. |
| Selection of participants into the study |
Moderate |
The estimate of used a combination of a hazard ratio for hospitalization among test-positive cases and an odds ratio for testing positive from a test-negative case control study. This domain is assessed as at moderate risk of bias because of the test negative design - 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 particular concerns in this domain - vaccination status is likely to be adequately measured. |
| Deviations from intervention |
Low |
No concerns in this domain - the study was observational. |
| Missing outcome data |
Moderate |
It is unclear how missing ethnicity data were addressed (they may have included missing as a category); also 7% of participants were not linked across data sources. |
| Measurement of the outcome |
Low |
No particular concerns in this domain - determination of the outcome is unlikely to be biased. |
| Selection of the reported results |
Moderate |
There is no evidence of an analysis plan, and we have concerns that results could have been selected for reporting because of the findings. |
| Overall risk of bias |
Moderate |
|
| Overall comment | Some concerns over the possibility of uncontrolled confounding given the observational nature of the data, and uncertainty in how missing data were addressed. |