Physical interventions to interrupt or reduce the spread of respiratory viruses
Version published: 30 January 2023 Version history
https://doi.org/10.1002/14651858.CD006207.pub6
Selection criteria
We included randomised controlled trials (RCTs) and cluster‐RCTs investigating physical interventions (screening at entry ports, isolation, quarantine, physical distancing, personal protection, hand hygiene, face masks, glasses, and gargling) to prevent respiratory virus transmission.
Primary outcomes
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Numbers of cases of viral respiratory illness
Influenza/COVID‐like illness
Pooling of nine trials conducted in the community found an estimate of effect for the outcomes of influenza/COVID‐like illness cases (risk ratio (RR) 0.95, 95% confidence interval (CI) 0.84 to 1.09; 9 trials; 276,917 participants; moderate‐certainty evidence; Analysis 1.1) suggesting that wearing a medical/surgical mask will probably make little or no difference for this outcome. Two studies in healthcare workers provided inconclusive results with very wide confidence intervals: RR 0.88, 95% CI 0.02 to 32; and RR 0.26, 95% CI 0.03 to 2.51, respectively (Jacobs 2009; MacIntyre 2015).
Laboratory‐confirmed influenza/SARS‐CoV‐2 cases
Similarly, the estimate of effect for laboratory‐confirmed influenza/SARS‐CoV‐2 cases (RR 1.01, 95% CI 0.72 to 1.42; 6 trials, 13,919 participants; moderate‐certainty evidence; Analysis 1.1) suggests that wearing a medical/surgical mask probably makes little or no difference compared to not wearing a mask for this outcome.
https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD006207.pub6/full?s=08
tl;dr Masks don't prevent the spread of respiratory illnesses.
The Paper is a Long Read with tons of data.