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, sex, race, body mass index, comorbidities, other vaccinations within 14 days, being in a long-term care facility, adequate dialysis dose, factors relating to immune deficiency, serum albumin and hospitalization within 14 days. It did not adjust for calendar time and symptoms at the time of potential vaccination, which are likely to be important confounders. |
| Selection of participants into the study |
Low |
No particular concerns in this domain. |
| Clasification of interventions |
Low |
No concerns in this domain - vaccination status was extracted from medical records. |
| Deviations from intervention |
Low |
No concerns in this domain - the study was observational. |
| Missing outcome data |
Low |
No concerns in this domain. |
| Measurement of the outcome |
Moderate |
For infection outcomes: Moderate risk of bias - It is stated that cases among fully vaccinated patients were investigated for confirmation of COVID-19 infection. It is unclear what is meant by this and therefore unclear whether the outcome was differentially ascertained among fully vaccinated patients compared to partially vaccinated or unvaccinated patients.
For severe disease: Low risk of bias - No concerns about measurement of this outcome. |
| Selection of the reported results |
Moderate |
There is no evidence of a protocol, and we have concerns that results could have been selected for reporting because of the findings. |
| Overall risk of bias |
Serious |
|
| Overall comment | The main concern is the potential for uncontrolled confounding, particularly by calendar time and symptoms at the time of potential vaccination. |