Although global vaccination efforts against SARS-CoV-2 are underway, the public is urged to continue using face masks as a primary intervention to control transmission. Recently, US public health officials have also encouraged doubling masks as a strategy to counter elevated transmission associated with infectious SARS-CoV-2 variants. US Centers for Disease Control and Prevention investigators reported that doubling masks increased effectiveness, but their assessment was limited in type and

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... inations of masks tested, as well as by the use of head forms rather than humans. To address these limitations, this study compared the fitted filtration efficiency (FFE) of commonly available masks worn singly, doubled, or in combinations.