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https://www.nature.com/articles/s41598-020-72798-7
Although mask wearing is intended, in part, to protect others from
exhaled, virus-containing particles, few studies have examined particle
emission by mask-wearers into the surrounding air. Here, we measured
outward emissions of micron-scale aerosol particles by healthy humans
performing various expiratory activities while wearing different types
of medical-grade or homemade masks. Both surgical masks and unvented
KN95 respirators, even without fit-testing, reduce the outward particle
emission rates by 90% and 74% on average during speaking and coughing,
respectively, compared to wearing no mask, corroborating their
effectiveness at reducing outward emission. These masks similarly
decreased the outward particle emission of a coughing superemitter, who
for unclear reasons emitted up to two orders of magnitude more
expiratory particles via coughing than average.
https://www.thelancet.com/journals/lancet/article/PIIS0140...
Our search identified 172 observational studies across 16 countries and
six continents, with no randomised controlled trials and 44 relevant
comparative studies in health-care and non-health-care settings
(n=25 697 patients). Transmission of viruses was lower with physical
distancing of 1 m or more, compared with a distance of less than 1 m;
protection was increased as distance was lengthened. Face mask use could result in a large reduction in risk of
infection, with stronger associations with N95 or similar
respirators compared with disposable surgical masks or similar. Eye protection also was
associated with less infection. Unadjusted studies and
subgroup and sensitivity analyses showed similar findings.
https://www.nature.com/articles/s41591-020-0843-2
We identified seasonal human coronaviruses, influenza viruses and
rhinoviruses in exhaled breath and coughs of children and adults with
acute respiratory illness. Surgical face masks significantly reduced
detection of influenza virus RNA in respiratory droplets and coronavirus
RNA in aerosols, with a trend toward reduced detection of coronavirus
RNA in respiratory droplets. Our results indicate that surgical face
masks could prevent transmission of human coronaviruses and influenza
viruses from symptomatic individuals.