Paper: "Effectiveness of surgical masks against influenza bioaerosols"

This was from a paper published in 2013 (abstract here). From the abstract:

Methods

      A dummy test head attached to a breathing simulator was used to test the performance of surgical masks against a viral challenge. Several designs of surgical masks commonly used in the UK healthcare sector were evaluated by measuring levels of inert particles and live aerosolised influenza virus in the air, from in front of and behind each mask.

Findings

      Live influenza virus was measurable from the air behind all surgical masks tested. The data indicate that a surgical mask will reduce exposure to aerosolised infectious influenza virus; reductions ranged from 1.1- to 55-fold (average 6-fold), depending on the design of the mask.

(H/t "Media And Government Officials Told Americans Not To Wear Masks. They Were Wrong"--The Federalist).

      On the same topic, see "Simple DIY masks could help flatten the curve. We should all wear them in public."--Washington Post. Excerpt:

       There are good reasons to believe DIY masks would help a lot. Look at Hong Kong, Mongolia, South Korea and Taiwan, all of which have covid-19 largely under control. They are all near the original epicenter of the pandemic in mainland China, and they have economic ties to China. Yet none has resorted to a lockdown, such as in China’s Wuhan province. In all of these countries, all of which were hit hard by the SARS respiratory virus outbreak in 2002 and 2003, everyone is wearing masks in public. George Gao, director general of the Chinese Center for Disease Control and Prevention, stated, “Many people have asymptomatic or presymptomatic infections. If they are wearing face masks, it can prevent droplets that carry the virus from escaping and infecting others.”

       My data-focused research institute, fast.ai, has found 34 scientific papers indicating basic masks can be effective in reducing virus transmission in public — and not a single paper that shows clear evidence that they cannot.

       Studies have documented definitively that in controlled environments like airplanes, people with masks rarely infect others and rarely become infected themselves, while those without masks more easily infect others or become infected themselves.

       Masks don’t have to be complex to be effective. A 2013 paper tested a variety of household materials and found that something as simple as two layers of a cotton T-shirt is highly effective at blocking virus particles of a wide range of sizes. Oxford University found evidence this month for the effectiveness of simple fabric mouth and nose covers to be so compelling they now are officially acceptable for use in a hospital in many situations. Hospitals running short of N95-rated masks are turning to homemade cloth masks themselves; if it’s good enough to use in a hospital, it’s good enough for a walk to the store.

       The reasons the WHO cites for its anti-mask advice are based not on science but on three spurious policy arguments. First, there are not enough masks for hospital workers. Second, masks may themselves become contaminated and pass on an infection to the people wearing them. Third, masks could encourage people to engage in more risky behavior.