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 |
| Randomization |
Low |
Quote: "random number generator software" "After assigning a three-digit randomization number to a participant, a sealed envelope with the randomization number was given to a healthcare worker who administered the vaccine"
Comment: Allocation sequence random. Allocation sequence probably concealed. Imbalances in baseline characteristics appear to be compatible with chance. |
| Deviations from intervention |
Low |
Quote: “The participants did not know which preparation they were receiving. After the vaccination, a separate physician observed the participant for possible adverse events (AE). The laboratory specialists were provided with the samples marked with coded numbers, and thus were also blinded.”
Comment: Blinded study (participants and personnel/carers). All available cases were analysed; no participants were excluded from analyses due to protocol violations. As we are assessing the effect of assignment to intervention, the analysis method performed on these outcomes was considered appropriate. Risk assessed to be low for the outcomes: Confirmed COVID. Mortality. Local adverse events. Systemic adverse events. Adverse events. |
| Missing outcome data |
Low |
Comment: 400 participants randomized; 398 participants analyzed.
Data available for nearly all participants randomized. Risk assessed to be some concerns for the outcomes: Confirmed COVID. Mortality. Local adverse events. Systemic adverse events. Adverse events. |
| Measurement of the outcome |
Low |
Comment: Method of measuring the outcome probably appropriate.
Measurement or ascertainment of outcome probably does not differ between groups. Blinded study (outcome assessor). Risk assessed to be low for the outcomes: Confirmed COVID. Mortality. Local adverse events. Systemic adverse events. Adverse events. |
| Selection of the reported results |
Some concerns |
Comment: The protocol and statistical analysis plan were not available and the registry was retrospective.
No information on whether the result was selected from multiple outcome measurements or analyses of the data. No information on whether the trial was analyzed as pre-specified. Risk assessed to be some concerns for the outcomes: Confirmed COVID. Mortality. Local adverse events. Systemic adverse events. Adverse events. |
| Overall risk of bias |
Some concerns |