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 only for age and calendar time. Uncontrolled confounding is likely. |
| 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 |
Moderate |
No information about missing data is reported, although there are likely to be some (e.g. people who moved out of state). |
| 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 an 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 | Concerns mainly over uncontrolled confounding. |