Preprint Review Version 2 This version is not peer-reviewed

Face Masks Against COVID-19: An Evidence Review

Version 1 : Received: 10 April 2020 / Approved: 12 April 2020 / Online: 12 April 2020 (17:41:10 CEST)
Version 2 : Received: 12 May 2020 / Approved: 13 May 2020 / Online: 13 May 2020 (13:16:04 CEST)

How to cite: Howard, J.; Huang, A.; Li, Z.; Tufekci, Z.; Zdimal, V.; van der Westhuizen, H.; von Delft, A.; Price, A.; Fridman, L.; Tang, L.; Tang, V.; Watson, G.L.; Bax, C.E.; Shaikh, R.; Questier, F.; Hernandez, D.; Chu, L.F.; Ramirez, C.M.; Rimoin, A.W. Face Masks Against COVID-19: An Evidence Review. Preprints 2020, 2020040203 (doi: 10.20944/preprints202004.0203.v2). Howard, J.; Huang, A.; Li, Z.; Tufekci, Z.; Zdimal, V.; van der Westhuizen, H.; von Delft, A.; Price, A.; Fridman, L.; Tang, L.; Tang, V.; Watson, G.L.; Bax, C.E.; Shaikh, R.; Questier, F.; Hernandez, D.; Chu, L.F.; Ramirez, C.M.; Rimoin, A.W. Face Masks Against COVID-19: An Evidence Review. Preprints 2020, 2020040203 (doi: 10.20944/preprints202004.0203.v2).

Abstract

The science around the use of masks by the general public to impede COVID-19 transmission is advancing rapidly. Policymakers need guidance on how masks should be used by the general population to combat the COVID-19 pandemic. Here,we develop an analytical framework to examine an overlooked aspect of mask usage: masks as source-control targeting egress from the wearer with benefits at the population-level, rather than as PPE used for ingress control for health-care workers with focus on individual outcomes. We consider and synthesize the relevant literature to inform multiple areas: 1) transmission characteristics of COVID-19, 2) filtering characteristics and efficacy of masks, 3) estimated population impacts of widespread community mask use, and 4) sociological considerations for policies concerning mask-wearing. A primary route of transmission of COVID-19 is likely via respiratory droplets, and is known to be transmissible from presymptomatic and asymptomatic individuals. Reducing disease spread requires two things: first, limit contacts of infected individuals via physical distancing and other measures, and second, reduce the transmission probability per contact. The preponderance of evidence indicates that mask wearing reduces the transmissibility per contact by reducing transmission of infected droplets in both laboratory and clinical contexts. Public mask wearing is most effective at reducing spread of the virus when compliance is high. The decreased transmissibility could substantially reduce the death toll and economic impact while the cost of the intervention is low. Given the current shortages of medical masks we recommend the adoption of public cloth mask wearing, as an effective form of source control for now, in conjunction with existing hygiene, distancing, and contact tracing strategies. We recommend that public officials and governments strongly encourage the use of widespread face masks in public, including the use of appropriate regulation.

Subject Areas

COVID-19; SARS-CoV-2; masks; pandemic

Comments (6)

Comment 1
Received: 13 May 2020
Commenter: Jeremy Howard
Commenter's Conflict of Interests: Author
Comment: Added new references that have been added in last month. Added more detail on Bae et al. Renamed some sections. Moved some paragraphs between sections. Fixed some notation issues. Added paragraph about face shields and other coverings. Fixed some grammar and style issues.
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Comment 2
Received: 18 May 2020
Commenter: JN
The commenter has declared there is no conflict of interests.
Comment: I don't think anyone really questions whether a new CLEAN mask applied correctly COULD offer some protection.

But what happens after an hour or 2 hours of using a cloth mask by an infected person? Haven't we now introduced a new vector for transmission, that is probably spraying more virus into the air, possibly even smaller virus particles that have evaporated and are now traveling further? In addition, you only need to spend 5 minutes watching how people are using masks to realize that they are actually touching this surface more than they might normally even touch their face.

This paper also fails to mention the outcome of the Seongman Bae study, that ALL of the masks showed more contamination on the OUTSIDE of the masks. And further, concluded that "both surgical and cotton masks seem to be ineffective in preventing the dissemination of SARS–CoV-2 from the coughs of patients with COVID-19 to the environment and external mask surface".
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Response 1 to Comment 2
Received: 20 May 2020
Commenter: Stephen Lowell
The commenter has declared there is no conflict of interests.
Comment: If you read the actual study (and the revealing comments between researchers) you will find this is not at all comparable to the current situation and this study is far from saying anything definitive about the lack of effectiveness of masks. First, this is a study looking at people coughing from 20 cm away. Nobody is saying it is safe to let a sick person cough in your face at a close distance just because they are wearing a mask. Masks are in addition to social distancing, not in place of it. In short, the Seongman Bae study did not aim to verify whether surgical or cloth masks are able to shorten the trajectory of droplets emitted through coughing, speaking or breathing. Second, and more to your point, in the study itself, compared with the control condition, the petri dish viral load was less with a cloth mask for all patients, and in half, was not detectable at all. Such reductions do help at the population level. So, the data from the study actually support mask-wearing, coupled with other measures, as a precautionary strategy.
Comment 3
Received: 19 May 2020
Commenter: Rami Mhanna
The commenter has declared there is no conflict of interests.
Comment: I could not download the article, but when it comes to single-layered cloth masks I find no logic in wearing them before validating in real-life scenarios.
The only real-life scenario studied so far by C Raina MacIntyre et al. in a Vietnamese hospital showed that cloth masks were significantly less effective than controls (normal practice which involves surgical masks) in preventing infection. The models all systematic reviews published so far indicate a lack of significance for wearing masks in public. When you have over 11 studies (B. J. COWLING et al. 2010) show lack of significance and suddenly one says there is significance for wearing a cloth mask I would get suspicious. The only significant difference found in the above mentioned systematic review was for a controlled experimental setup where volunteers where asked to cough towards a petri dish and showed that nothing was on the petri dish compared to volunteers not wearing masks. The study did not investigate the leaked particles from the sides of the mask which in a real-life scenario might be even more scary than those coming directly out of the subject.
There are many conditions that need to be taken into account when considering cloth masks, like humidity, the concentration of viral droplets in the environment, whether the purpose is to protect others or protect from others, whether the subject is touching the mask, whether there are viruses on the surface around the subject. If the protection is less than 5% better than a control, then it should not be adopted in my opinion.
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Response 1 to Comment 3
Received: 25 May 2020
Commenter: Paul V Sullivan
The commenter has declared there is no conflict of interests.
Comment: Face Mask Use and Control of Respiratory Virus Transmission in Households - MacIntyre, CR et al - Emerging Infectiuos Diseases - Feb-2009

The authors state that masks are effective, but in households the compliance was less than 50%. Doesn't help if you don't wear it.

The above article is freely downloadable.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2662657/
Comment 4
Received: 21 May 2020
The commenter has declared there is no conflict of interests.
Comment: With supply of surgical masks slowly being restored (soon there should be no more shortage) recommendation of surgical masks over cloth masks should be made, given that they use of surgical masks by public should in no way affect supply to healthcare workers.
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