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: "Eligible participants were sequentially assigned a study number at enrolment and were vaccinated according to the randomisation list prepared by an independent statistician. Study medications were allocated to codes by block randomisation using a computerised randomisation scheme generator"
Comment: Allocation sequence random. Allocation sequence concealed. |
| Deviations from intervention |
Low |
Quote: “the unblinded study personnel prepared the vaccine or placebo out of sight of the participants, using opaque syringes to ensure masking since the vaccine and placebo are visually different” (report) "Masking: Single (Participant)" (registry)
Comment: Single blinded study (participants were blinded, personnel/carers were not blinded). Deviations from intended intervention arising because of the study context: No participant cross-over. Hence, deviations did not arise because of the trial context. Data for the outcome were analyzed using intention-to-treat analysis. This method was considered appropriate to estimate the effect of assignment to intervention. Risk assessed to be low for the outcomes: Specific antibody GMTs. Neutralizing antibody GMTs. Cellular response. Local adverse events. Systemic adverse events. Adverse events. Serious adverse events. |
| Missing outcome data |
Low |
Comment: 44 participants randomized; 44 participants analyzed.
Data available for all participants randomized. Risk assessed to be low for the outcomes: Specific antibody GMTs. Neutralizing antibody GMTs. Cellular response. Local adverse events. Systemic adverse events. Adverse events. Serious adverse events. |
| Measurement of the outcome |
Some concerns |
Comment: Method of measuring the outcome probably appropriate.
Measurement or ascertainment of outcome probably does not differ between groups. Unblinded study (outcome assessor). SPECIFIC ANTIBODY GMT. NEUTRALIZING ANTIBODY GMT. CELLULAR RESPONSE. Immunogenicity assays are observer-reported outcomes not involving judgement. Risk assessed to be low for the outcomes: Specific antibody GMT. Neutralizing antibody GMT. Cellular response. LOCAL, SYSTEMIC, ADVERSE and SERIOUS ADVERSE EVENTS The authors reported on adverse events that may contain both clinically- and laboratory-detected events, which can be influenced by knowledge of the intervention assignment, but is not likely in the context of the pandemic. Risk assessed to be some concerns for the outcomes: Local adverse events. Systemic adverse events. Adverse events. Serious adverse events. |
| Selection of the reported results |
Low |
Comment: The prospective trial registry was available (dated 28 August 2020).
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 GMTs. Neutralizing antibody GMTs. Cellular response. Local adverse events. Systemic adverse events. Adverse events. Serious adverse events. |
| Overall risk of bias |
Some concerns |