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: "The randomization list was generated by an independent statistician using SAS software (version 9.4, SAS Institute Inc, CA, USA). A unique randomization number in sequence was allocated to each participant, who then received a vaccine or placebo dose labelled with the same randomization number. The individuals involved in the randomization and masking had no involvement in the rest of the trial."
Comment: Allocation sequence random. Allocation sequence concealed. Imbalances in baseline characteristics appear to be compatible with chance. |
| Deviations from intervention |
Low |
Quote: "The participants, investigators, and staff performing lab testing were all masked to the patients’ treatment allocations."
Comment: Blinded study (participants, personnel, investigators). All randomized participants who received at least one dose were analysed for safety outcomes. As we are assessing the effect of assignment to intervention, the analysis method performed on these safety outcomes, was considered appropriate. Risk assessed to be low for outcomes: Specific antibody GMT. Neutralizing antibody GMT Local adverse events. Systemic adverse events. Adverse events. Total adverse events. Serious adverse events. |
| Missing outcome data |
Low |
Comment: 500 participants randomized; 500 participants analyzed for safety outcomes; 494 participants analyzed for immunogenicity outcomes.
Data available for all participants randomized. Risk assessed to be low for outcomes: Specific antibody GMT. Neutralizing antibody GMT. Local adverse events. Systemic adverse events. Adverse events. Total adverse events. Serious 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: Specific antibody GMT. Neutralizing antibody GMT. Local adverse events. Systemic adverse events. Adverse events. Total adverse events. Serious adverse events. |
| Selection of the reported results |
Low |
Comment: The prospective trial registry was available.
Outcome 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. Local adverse events. Systemic adverse events. Adverse events. Total adverse events. Serious adverse events. |
| Overall risk of bias |
Low |