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 |
Quotes: "Randomisation lists, using block randomisation stratified by study cohort, was generated by an independent statistician using SAS software (version 9.4). Block sizes were chosen to align with the study cohort sizes. Individuals involved in randomisation and masking had no involvement in the rest of the trial" "The experimental vaccines and placebos had identical packaging with a randomisation number on each vial as the only identifiers"
Comment: Allocation sequence random. Allocation sequence concealed. |
| Deviations from intervention |
Low |
Quote: "Investigators, participants, and laboratory staff were masked to treatment assignment"
Comment: Blinded study (participants and personnel/carers). Intention-to-treat (ITT) analysis or modified ITT analysis. 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: Specific antibody GMT, Neutralizing antibody GMT, Cellular response, Local adverse events, Systemic adverse events, and Adverse events. |
| Missing outcome data |
Low |
Comment: 250 participants randomized (older adults cohort); 248 to 250 participants analyzed (depending on the outcome).
Data available for all or nearly all participants randomized. Risk assessed to be low for the outcomes: Confirmed symptomatic COVID, Confirmed severe COVID, Specific antibody GMT, Neutralizing antibody GMT, Cellular response, Local adverse events, Systemic adverse events, and 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 symptomatic COVID, Confirmed severe COVID, Specific antibody GMT, Neutralizing antibody GMT, Cellular response, Local adverse events, Systemic adverse events, and Adverse events. |
| Selection of the reported results |
Low |
Comment: The registry was available (dated September 28, 2020).
Outcomes below were pre-specified. Results were not selected from multiple outcome measurements or analyses of the data. Trial analyzed as pre-specified. Risk assessed to be low for the outcomes: Specific antibody GMT, Neutralizing antibody GMT, Cellular response, Local adverse events, Systemic adverse events, and Adverse events. Confirmed symptomatic COVID and Confirmed severe COVID outcomes were not pre-specified in the registry, however, we do not consider the reporting of this outcome to be selective since it should be reported that there were no cases even if not planned. Results were probably not selected from multiple outcome measurements or analyses of the data. Trial analyzed as pre-specified. Risk assessed to be low for the outcomes: Confirmed symptomatic COVID and Confirmed severe COVID. |
| Overall risk of bias |
Low |