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: "The study statisticians adjusted a software for randomization using the minimization method weighing the following factors: age (categories: 18-45, 45-64, 65-74, 75-79 years), the type of anticipated contacts with SARS-CoV-2 (confirmed SARS-CoV-2 infection cases within the "red" zone, working closely with colleagues who had proven contacts with SARS-CoV-2 patients). A study coordinator sequentially assigned participants. The assignments were open to investigators and participants"
Comment: Allocation sequence random. Unclear allocation sequence concealment. |
| Deviations from intervention |
Low |
Quote: "The assignments were open to investigators and participants."
Comment: Unblinded study (participants and personnel/carers). Deviations from intended intervention arising because of the study context: No participant cross-over. Occasional non-adherence reported in 4/25 intervention participants. Other prophylaxis reported (Vitamin D/C) with no significant difference between groups. All participants in both groups wore PPE. No co-interventions of interest (vaccines) were available at the time of the study. 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: Symptomatic or asymptomatic confirmed COVID-19. Confirmed COVID-19. Confirmed symptomatic COVID-19. Hospital admissions or death. ICU admissions or death. Mortality. Adverse events. |
| Missing outcome data |
Low |
Comment: 50 participants randomized; 50 participants analyzed.
Data available for all participants randomized. Risk assessed to be low for the outcomes: Symptomatic or asymptomatic confirmed COVID-19. Confirmed COVID-19. Confirmed symptomatic COVID-19. Hospital admissions or death. ICU admissions or death. Mortality. 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) CONFIRMED COVID-19, CONFIRMED SYMPTOMATIC COVID-19, MORTALITY Mortality and PCR status do not involve judgement. Risk assessed to be low for outcome: Confirmed COVID-19. Confirmed symptomatic COVID-19. Mortality. ICU ADMISSION OR DEATH For this outcome, we do not consider that the assessment cannot possibly be influenced by knowledge of intervention assignment. Risk assessed to be low for the outcome: ICU admission or death. SYMPTOMATIC OR ASYMPTOMATIC CONFIRMED COVID-19, HOSPITAL ADMISSION OR DEATH, ADVERSE EVENTS Although mortality does not involve judgement, hospital admission could be influenced by knowledge of intervention assignment but was not considered likely to in the context of a pandemic. Incidence of symptomatic COVID-19 and adverse events may contain clinically-detected and patient-reported outcomes which can be influenced by knowledge of intervention assignment but is not considered likely to in the context of a pandemic. Risk assessed to be some concerns for the outcomes: Symptomatic or asymptomatic confirmed COVID-19. Hospital admission or death. Adverse events. |
| Selection of the reported results |
Some concerns |
Comment: The trial registry was available.
SYMPTOMATIC OR ASYMPTOMATIC CONFIRMED COVID, ADVERSE EVENTS Different timepoint pre-specified for the outcome. No information on whether results were selected from multiple outcome measurements or analyses of the data. Trial probably not analyzed as pre-specified. Risk assessed to be some concerns for the outcomes: Symptomatic or asymptomatic confirmed COVID-19. Adverse events. CONFIRMED COVID, CONFIRMED SYMPTOMATIC COVID, HOSPITAL ADMISSIONS OR DEATH, ICU ADMISSIONS OR DEATH, MORTALITY Outcome not pre-specified. No information on whether results were selected from multiple outcome measurements or analyses of the data. No information on whther trial was analyzed as pre-specified. Risk assessed to be some concerns for the outcomes: Confirmed COVID-19. Confirmed symptomatic COVID-19. Hospital admissions or death. ICU admissions or death. Mortality. |
| Overall risk of bias |
Some concerns |