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Background

The Association of American Physicians and Surgeons asserts that cloth masks are not a way to meaningfully protect someone against COVID-19 nor against source-control. According to their website:

Introduction

COVID-19 is as politically-charged as it is infectious. Early in the COVID-19 pandemic, the WHO, the CDC and NIH’s Dr. Anthony Fauci discouraged wearing masks as not useful for non-health care workers. Now they recommend wearing cloth face coverings in public settings where other social distancing measures are hard to do (e.g., grocery stores and pharmacies). The recommendation was published without a single scientific paper or other information provided to support that cloth masks actually provide any respiratory protection. Let’s look at the data.

The theory behind mask wearing:

Source control: Cloth mask can trap droplets that come out of a person’s mouth when they cough or sneeze. Protection: Personal Protective Equipment (PPE) – only N95 masks

This seems striking to me, as nearly every country has required that its' citizens wear face masks including cloth masks, all over or in portions of the country with few exceptions. And there are no businesses in countries like the United States that I know of that prevent people from entering if they wear cloth masks. This near agreement on overarching mask restrictions seems to be in partial contradiction to the Association of American Physicians and Surgeons prompted me to ask:

Question

When the WHO, CDC, and/or NIH made the recommendation to wear cloth masks in public settings, was there a single scientific paper they cited that supported that cloth masks provide any respiratory protection?

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As far as the WHO is concerned, they seem to only have changed their recommendation in June (much later than the CDC). Also note that it's a red herring what AAPS says about "respiratory protection" (which they define as excluding "source control") because e.g. the WHO never seems to have claimed that cloth masks act as PPE for the wearer in a significant fashion (so why should the WHO be expected to provide evidence for something they didn't claim?)

The new [WHO] guidance recommends that the general public wear cloth masks made from at least three layers of fabric “on public transport, in shops, or in other confined or crowded environments.” It also says people over 60 or with preexisting conditions should wear medical masks in areas where there’s community transmission of the coronavirus and physical distancing is impossible, and that all workers in clinical settings should wear medical masks in areas with widespread transmission.

It’s a major update to the agency’s April 6 recommendations, which said members of the general public “only need to wear a mask if you are taking care of a person with Covid-19” or “if you are coughing or sneezing.” And it’s important advice for countries around the world battling the virus, especially those in South America, the Middle East, and Africa, where the rate of Covid-19 transmission appears to be accelerating.

At a WHO press conference on June 3, Michael Ryan, an infectious disease epidemiologist and the executive director of the WHO’s Health Emergencies Programme, said WHO still believes that masks should primarily be used “for purposes of source control — in other words, for people who may be infectious, reducing the chances that they will infect someone else.”

Also

To develop the guidance, the agency consulted with a range of international experts from different countries and disciplines such as infectious diseases and epidemiology. Their review of a variety of evidence demonstrated some new findings, including that face protections, including respirators or medical masks, can result in a large reduction of transmission of coronaviruses, including COVID-19.

Recommendations, such as those regarding fabric masks, are the result of new research that the WHO commissioned that was not available a month ago. This new evidence, said Dr Maria Van Kerkhove, WHO Technical Lead, has shown that the recommended fabric combination "can actually provide a mechanistic barrier that if someone were infected with COVID-19, you can prevent those droplets from going through and infecting someone."

So, yeah, the WHO waited until they could point out to more research before changing/making their recommendation, but even that was for "source control". (Whether that was the right or wrong approach is a different matter, and I'm not gonna get into that here.)

So, again why should the WHO be expected to provide evidence for something they didn't claim (in re "respiratory protection" as AAPS defines it)?

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True

The CDC changed course on April 3:

"The Coronavirus Crisis: CDC Now Recommends Americans Consider Wearing Cloth Face Coverings In Public", npr,org April 3, 20205:49 PM ET

On that day April 3 a webpage from the CDC went live called "Recommendation Regarding the Use of Cloth Face Coverings, Especially in Areas of Significant Community-Based Transmission" under the heading tab "Prevent Getting Sick". And it did not have a single reference to support its findings:

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This is the entire text the public got to see on the web when the CDC made the recommendation on April 3:

CDC continues to study the spread and effects of the novel coronavirus across the United States. We now know from recent studies that a significant portion of individuals with coronavirus lack symptoms (“asymptomatic”) and that even those who eventually develop symptoms (“pre-symptomatic”) can transmit the virus to others before showing symptoms. This means that the virus can spread between people interacting in close proximity—for example, speaking, coughing, or sneezing—even if those people are not exhibiting symptoms. In light of this new evidence, CDC recommends wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain (e.g., grocery stores and pharmacies) especially in areas of significant community-based transmission.

It is critical to emphasize that maintaining 6-feet social distancing remains important to slowing the spread of the virus. CDC is additionally advising the use of simple cloth face coverings to slow the spread of the virus and help people who may have the virus and do not know it from transmitting it to others. Cloth face coverings fashioned from household items or made at home from common materials at low cost can be used as an additional, voluntary public health measure.

The cloth face coverings recommended are not surgical masks or N-95 respirators. Those are critical supplies that must continue to be reserved for healthcare workers and other medical first responders, as recommended by current CDC guidance.

This recommendation complements and does not replace the President’s Coronavirus Guidelines for America, 30 Days to Slow the Spread, which remains the cornerstone of our national effort to slow the spread of the coronavirus. CDC will make additional recommendations as the evidence regarding appropriate public health measures continues to develop.

To be fair, while the claim is true that the CDC published a recommendation that did not have a single supporting study cited: Later they added some links to that page. Unfortunately, none of relevance to anyhow 'prove' cloth masks would offer any benefit — in fact, never ever even later than that on this constantly updated page to support their recommendations with reliable evidence. Only some scaremongering people into the belief that asymptomatic spread would be the main driver of spread. And only some that as per mechanistic plausibility would suggest that (mandated) masks in community settings would or could somehow 'help'.

On April 5 the CDC added the following references:

Recent Studies:
Rothe C, Schunk M, Sothmann P, et al. Transmission of 2019-nCoV Infection from an Asymptomatic Contact in Germany. The New England journal of medicine. 2020;382(10):970-971.
Zou L, Ruan F, Huang M, et al. SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. The New England journal of medicine. 2020;382(12):1177-1179.
Pan X, Chen D, Xia Y, et al. Asymptomatic cases in a family cluster with SARS-CoV-2 infection. The Lancet Infectious diseases. 2020.
Bai Y, Yao L, Wei T, et al. Presumed Asymptomatic Carrier Transmission of COVID-19. Jama. 2020.
Kimball A HK, Arons M, et al. Asymptomatic and Presymptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility — King County, Washington, March 2020. MMWR Morbidity and mortality weekly report. 2020; ePub: 27 March 2020.
Wei WE LZ, Chiew CJ, Yong SE, Toh MP, Lee VJ. Presymptomatic Transmission of SARS-CoV-2 — Singapore, January 23–March 16, 2020. MMWR Morbidity and mortality weekly report. 2020;ePub: 1 April 2020.
Li R, Pei S, Chen B, et al. Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2). Science (New York, NY). 2020.

As evidenced by those studies: None 'covering' any type of mask.

Of note is that the very first study cited by the CDC is of the same quality as the others of those quoted: 'dubious':

So, that paper we all reported on showing transmission of #2019nCoV from an “asymptomatic case”? Well, it turns out the woman did have symptoms. Here’s what we know so far:

Study claiming new coronavirus can be transmitted by people without symptoms was flawed A traveler to Germany from China who infected another person did feel ill, contradicting New England Journal of Medicine report

kakape (on Twitter 12:00 AM · Feb 4, 2020)

Highlighting his scoop published in Science:

— Kai Kupferschmidt: "Study claiming new coronavirus can be transmitted by people without symptoms was flawed", Science, Feb. 3, 2020 , 5:30 PM

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