Mask facts: A cluster randomized trial of cloth masks compared with medical masks in health care workers (1600) was conducted on 2015 involving flu and flu like transmissions. The rates of all infections were highest in the cloth cloth mask use. Penetration of cloth masks by particles was almost 97% and medical masks 44%.
“The results caution against the use of cloth masks. This is an important finding to inform occupational health and safety....moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection.” April 2015.
WHO website: “There is limited evidence that wearing a medical mask by healthy individuals in households, in particular those who share a house with a sick person, or amping attendees...of mass gatherings may be beneficial as a measure preventing transmission...At present, there is no direct evidence...on the effectiveness...of universal masking of healthy people in the community to prevent infection with respiratory virus, including COVID-19.” June 5, 2020.
NATURE publication of April 2020: RESPIRATORY VIRUS SHEDDING IN EXHALED BREATH AND EFFICACY OF FACE MASKS. “Among the samples of collected without a face mask, we found that the majority of participants with influenza virus and coronavirus infection did not shed detectable virus in respiratory droplets or aerosols. For those who did shed virus in respiratory droplets and aerosols, viral load in both (masked or unmasked) tended to be low.” The major limitation of our study was the large proportion of participants with undetectable viral shedding in exhaled breath for each of the viruses studied. We could have increased the sampling duration beyond 30 minutes to increase the viral shedding being captured.” May 27, 2020.