TABLE 1.
Certainty of evidence evaluated with Grading of Recommendations Assessment, Development, and Evaluation (GRADE) framework for primary outcomes
| Comparisons (vs. control) | Comparison no. | OR (95% CI), p‐value | Study design a | Risk of bias | Inconsistency | Indirectness | Imprecision | Publication bias | GRADE |
|---|---|---|---|---|---|---|---|---|---|
| Overall mask effect | |||||||||
| Preventive effect of wearing mask (any type) on respiratory viral infection | |||||||||
| Overall respiratory viral infection | 22 | 0.50 (0.37, 0.68), p < 0.001 | Observational study | Not serious | Not serious | Not serious | Not serious | Not serious | Low |
| Influenza | 8 | 0.71 (0.42, 1.21), p = 0.208 | RCT | Not serious | Not serious | Not serious | Serious | Not serious | Moderate |
| SARS/MERS | 6 | 0.30 (0.14, 0.63), p = 0.001 | Observational study | Serious | Not serious | Not serious | Not serious | Not serious | Low b |
| COVID‐19 | 8 | 0.49 (0.31, 0.78), p = 0.003 | Observational study | Not serious | Not serious | Not serious | Not serious | Not serious | Low |
| Compliance (vs. low compliance) | |||||||||
| High adherence to mask behaviour | 6 | 0.43 (0.23, 0.82), p = 0.010 | Observational study | Not serious | Serious | Not serious | Not serious | Not serious | Very low |
| Per specific mask type | |||||||||
| Influenza virus infection | |||||||||
| Medical and surgical mask | 17 | 0.75 (0.51, 1.09), p = 0.132 | RCT | Not serious | Not serious | Not serious | Serious | Not serious | Moderate |
| N95 or equivalent | 11 | 0.84 (0.56, 1.28), p = 0.417 | RCT | Not serious | Not serious | Not serious | Serious | Not serious | Moderate |
| Non‐medical mask | 1 | 1.29 (0.24, 6.94), p = 0.767 | Observational study | Not serious | Not serious | Not serious | Very serious | Not serious | Very low |
| Coronavirus infection, overall (SARS, MERS, and COVID‐19) | |||||||||
| N95 or equivalent | 14 | 0.30 (0.20, 0.44), p < 0.001 | Observational study | Not serious | Not serious | Not serious | Not serious | Serious | Low b |
| Medical or surgical mask | 14 | 0.72 (0.51, 1.01), p = 0.057 | Observational study | Not serious | Not serious | Not serious | Serious | Serious | Very low |
| Non‐medical mask | 2 | 0.77 (0.29, 2.07), p = 0.605 | Observational study | Not serious | Not serious | Not serious | Serious | Serious | Very low |
| SARS/MERS infection | |||||||||
| N95 or equivalent | 8 | 0.24 (0.13, 0.46), p < 0.001 | Observational study | Not serious | Not serious | Not serious | Not serious | Serious | Low b |
| Medical and surgical mask | 7 | 0.70 (0.38, 1.30), p = 0.259 | Observational study | Not serious | Not serious | Not serious | Serious | Serious | Very low |
| COVID‐19 infection | |||||||||
| N95 or equivalent | 6 | 0.30 (0.17, 0.55), p < 0.001 | Observational study | Not serious | Not serious | Not serious | Not serious | Serious | Low b |
| Medical or surgical mask | 7 | 0.71 (0.44, 1.14), p = 0.156 | Observational study | Serious | Not serious | Not serious | Serious | Serious | Very low |
| Non‐medical mask | 2 | 0.73 (0.25, 2.14), p = 0.566 | Observational study | Not serious | Not serious | Not serious | Serious | Serious | Very low |
| Health care settings | |||||||||
| Influenza virus infection | |||||||||
| Medical or surgical mask | 10 | 0.65 (0.28, 1.49), p = 0.309 | RCT | Not serious | Not serious | Not serious | Serious | Not serious | Moderate |
| N95 or equivalent | 9 | 0.72 (0.31, 1.69), p = 0.451 | RCT | Not serious | Not serious | Not serious | Serious | Not serious | Moderate |
| Non‐medical mask | 1 | 1.29 (0.24, 6.94), p = 0.767 | Observational study | Not serious | Not serious | Not serious | Very serious | Not serious | Very low |
| Coronavirus infection, overall (SARS, MERS, and COVID‐19) | |||||||||
| N95 or equivalent | 14 | 0.29 (0.19, 0.44), p < 0.001 | Observational study | Not serious | Not serious | Not serious | Not serious | Serious | Low b |
| Medical or surgical mask | 12 | 0.69 (0.44, 1.07), p = 0.097 | Observational study | Serious | Not serious | Not serious | Serious | Serious | Very low |
| Community settings | |||||||||
| Influenza virus infection | |||||||||
| Medical or surgical mask | 7 | 0.76 (0.47, 1.20), p = 0.239 | RCT | Serious | Not serious | Not serious | Serious | Not serious | Low |
| N95 or equivalent | 2 | 3.50 (0.44, 27.97), p = 0.237 | RCT | Not serious | Not serious | Not serious | Very serious | Not serious | Low |
| Coronavirus infection, overall (SARS, MERS, and COVID‐19) | |||||||||
| Medical or surgical mask | 2 | 0.78 (0.53, 1.12), p = 0.150 | Observational study | Serious | Not serious | Not serious | Serious | Not serious | Very low |
| Non‐medical mask | 1 | 1.29 (0.48, 3.45), p = 0.612 | Observational study | Not serious | Not serious | Not serious | Serious | Not serious | Very low |
Note: Statistically significant results are marked in bold.
Abbreviations: CI, confidence interval; GRADE, Grading of Recommendations Assessment, Development, and Evaluation; MERS, Middle East respiratory syndrome; OR, odds ratio; RCT, randomized controlled trial; SARS, severe acute respiratory syndrome.
Dominant study design.
Upgraded by one for a large magnitude of effect.
Rationale:
Study design: If randomized trials form the majority of evidence base, the quality rating starts at ‘high’. If observational studies form the majority of evidence, base the quality rating starts at ‘low’.
Risk of bias: Downgraded for failure to conceal random allocation or blind participants in randomized controlled trials or failure to adequately control for confounding in observational studies.
Inconsistency: Downgraded if direct and indirect evidence are not coherence as demonstrated by the difference in point estimates and the lack of overlap in the 95% confidential intervals (CIs) between direct and indirect evidence (Global incoherence tests such as Q statistic to assess consistency under the assumption of a full design‐by‐treatment interaction random effects model were used as supplementary information for judgement).
Indirectness. Downgraded if there present substantial differences in study characteristics (PICO) that may modify treatment effect in the direct comparisons (such as A v C and B v C) that form the basis for the indirect estimate of effect of the comparison of interest (A v B), or the result is solely derived from indirect comparisons.
Imprecision: Downgraded when cases are small; or 95% CIs are wide and include or are close to null effect.
Publication bias: Downgraded when substantial asymmetry is observed in funnel plot or p < 0.10 in egger's test.
GRADE Definition (suggested by Puhan et al. in ‘A GRADE Working Group approach for rating the quality of treatment effect estimates from network meta‐analysis’):
High quality: We are very confident that the true effect lies close to that of the estimate of the effect.
Moderate quality: We are moderately confident in the effect estimate that is the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.
Low quality: Our confidence in the effect estimate is limited that is the true effect may be substantially different from the estimate of the effect.
Very low quality: We have very little confidence in the effect estimate that is the true effect is likely to be substantially different from the estimate of effect.