Trial NCT05158855
Publication Sung J, Vaccines, 2022
Primary outcome on the report: During the blood sampling period, primary safety end points were assessed, including not only local reactions and systemic events, but also unsolicited adverse events and serious adverse events; All participants were observed for 1 h after the administration of booster or placebo to identify any immediate adverse events. Furthermore, 5 mL blood samples were drawn on days 0, 14, 35 and 49 for safety and immunogenicity assessments.

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
Some concerns 		Quote: "participants from 21–62 years old were randomly assigned into the active booster or placebo groups."
Comment: Allocation sequence probably random.
No information on allocation concealment.
Deviations from intervention
Low 		Quote: "observer-blinded" trial.
Comment: Unblinded study (participants unblinded; observer-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.
ITT analysis (with N randomized denominators).
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 the outcomes: Mortality, Systemic adverse events, Adverse events and Serious adverse events.
Missing outcome data
Low 		Comment: 16 participants randomized; 16 participants analyzed; no missing data.
Data available for all participants randomized.
Risk assessed to be low for the outcomes: Mortality, Systemic adverse events, adverse events and 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 (for self-assessment).

MORTALITY
Observer-reported outcome not involving judgement.
Risk assessed to be low for the outcome: Mortality

SYSTEMIC, ADVERSE EVENTS 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: Systemic adverse events, adverse events and Serious adverse events.
Selection of the reported results
Low 		Comment: The prospective registry was available (dated December 15, 2021).
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: Mortality, Systemic adverse events, adverse events and Serious adverse events.
Overall risk of bias
Some concerns