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 and comorbidities. Geographic location and health-seeking behaviour were similar due to restriction of the study design. Our prespecified important confounding domains of sex, socioeconomic status, ethnicity were not controlled for, leading to a likelihood of uncontrolled confounding. |
| Selection of participants into the study |
Serious |
9% of participants (55/638) were selected from hospitalized patients in COVID wards and ICUs. Additionally, purposive sampling was used in the study, but the characteristics used in selection were not reported. |
| Clasification of interventions |
Serious |
Vaccination status was based on self-report collected retrospectively. It is likely that most participants were given vaccination cards during the pandemic’s vaccination campaign in India, though this is not reported. |
| Deviations from intervention |
Low |
No concerns in this domain - the study was observational. |
| Missing outcome data |
Low |
Data appear to be complete for vaccination status, confounders and outcomes. |
| Measurement of the outcome |
Low |
No particular concerns in this domain - determination of infection 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 about uncontrolled confounding, self-reported vaccination status and possibility of some selection bias in how the sample was assembled. |