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 |
Information was collected on most key confounders (aside from socio-economic status, health-seeking behaviour, and covid symptoms at time of potential vaccination). The analysis was adjusted for site, age, sex, and race/ethnicity, and was stratified by time (admission date). Authors reported that there was no evidence to support including any other confounders in the model. |
| Selection of participants into the study |
Moderate |
Test-negative design. Additionally, partially vaccinated people (those who had received only 1 dose or received their second dose <14 days before their PCR test) were excluded from the analysis. |
| Clasification of interventions |
Low |
No particular concerns in this domain - vaccination status is likely to be adequately measured (obtained from electronic health records). |
| Deviations from intervention |
Low |
No concerns in this domain - the study was observational. |
| Missing outcome data |
Low |
No particular concerns in this domain - complete data on vaccination status and confounders for >95% of participants. |
| Measurement of the outcome |
Low |
No particular concerns regarding determination of SARS-CoV-2 status among hospitalised patients. |
| Selection of the reported results |
Moderate |
No protocol or analysis plan seen. |
| Overall risk of bias |
Moderate |
|
| Overall comment | Some concerns regarding residual confounding and bias in the selection of participants into the study. |