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 |
Serious |
The analysis adjusted for age group, sex, week of the analysis period and region of the province, but did not adjust for socioeconomic status, ethnicity, specific populations, comorbidities, COVID-19 symptoms at the time of potential vaccination hospitalisation and need for health care. |
| 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 conerns in this domain - the study made use of vaccine registers. |
| Deviations from intervention |
Low |
No concerns in this domain - the study was observational. |
| Missing outcome data |
Moderate |
There was a lack of information on missing data and its potential impact on the study results. |
| Measurement of the outcome |
Low |
No issues in this domain. |
| Selection of the reported results |
Moderate |
There is no evidence of a protocol/analysis plan, and we have concerns that results could have been selected for reporting because of the findings. |
| Overall risk of bias |
Serious |
|
| Overall comment | The pre-print article and supplementary material were used in data extraction and risk of bias assessment. The study assessed SARS-CoV-2 infection and hospitalization vaccine effectiveness in British Columbia (analysed here) and Quebec (analysed separately) using a test-negative case control design adjusting for age, sex, week, and region.
Concerns over uncontrolled confounding and the lack of a statistical analysis plan. |