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 |
The analysis adjusted (using propensity score matching) for age, sex, race, ethnicity, number of prior PCR tests, and geographic location (zip code). Uncontrolled confounding remains likely, e.g. by comorbidities. |
| Selection of participants into the study |
Low |
No particular concerns. Eligible vaccinated participants were matched (1:10) with unvaccinated participants using propensity score matching based on identified predictors. |
| Clasification of interventions |
Low |
No particular concerns. Groups were defined by vaccination status (single dose of Johnson & Johnson) as recorded in electronic health records. |
| Deviations from intervention |
Low |
No concerns in this domain - the study was observational. |
| Missing outcome data |
Low |
There were no missing data for intervention status, since no vaccine information was assumed to be not vaccinated. There were some ‘unknowns’ for covariates such as race and ethnicity (Table 1), but percentages were smaller than 2%. |
| Measurement of the outcome |
Low |
No particular concerns in this domain - determination of the outcome 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 | Some concerns about uncontrolled confounding. |