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 adjusted for age, gender age, sex, nationality group, and the competing risks of vaccination and death. Geographic location, comorbidities, health-seeking behaviour and specific subpopulation (e.g. healthcare worker/elderly in institution/pregnancy) were similar due to restriction of the study design. It is unclear whether our prespecified important confounding domains socioeconomic status and ethnicity were addressed when adjusting for nationality group, although we do not think these will be major confounders in this population. It is also unclear which factors are considered when adjusting for competing risks of vaccination and death and whether these are equivalent to the confounding domains symptoms at time of planned vaccination and hospitalization and need for health. There remains a likelihood of uncontrolled confounding given the observational nature of the data. |
| Selection of participants into the study |
Low |
No particular concerns in this domain. |
| 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 |
Low |
Almost all of those identified were included in the analysis. |
| Measurement of the outcome |
Low |
No particular concerns in this domain - determination of the outcomes is unlikely to be biased. |
| Selection of the reported results |
Moderate |
There is no evidence of a protocol, analysis plan or study registry and we have concerns that results could have been selected for reporting because of the findings. |
| Overall risk of bias |
Moderate |
|
| Overall comment | Concerns mainly about the possibility of uncontrolled confounding. |