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https://www.cdc.gov/coronavirus/2019-ncov/more/masking-science-sars-cov2.html https://www.cdc.gov/coronavirus/2019-ncov/more/masking-scien... https://www.nature.com/articles/d41586-020-02801-8 https://www.nature.com/articles/d41586-020-02801-8