The URL can be used to link to this page

Home My WebLink AboutMinutes - Read Before Packet - 5/26/2020 - Memorandum From Delynn Coldiron Re: Leadership Planning Team Meeting Minutes - May 26, 2020City Clerk 300 LaPorte Avenue PO Box 580 Fort Collins, CO 80522 970.221.6515 970.221-6295 - fax fcgov.com/cityclerk MEMORANDUM DATE: May 26, 2020 TO: Mayor and Councilmembers FROM: Delynn Coldiron, City Clerk RE: Leadership Planning Team (LPT) Meeting Mayor Wade Troxell (by video-conference call), Mayor Pro Tem Kristin Stephens (by video-conference call), City Manager Darin Atteberry (by video-conference call), Deputy City Manager Kelly DiMartino (by video-conference call), City Attorney Carrie Daggett (by video-conference call) and City Clerk Delynn Coldiron (by video-conference call) met on Tuesday, May 26, and the following summarizes the discussions that began at 7:09 a.m. May 26 Adjourned Meeting: The May 26 agenda items were reviewed. • COVID Update – Tom Gonzales, Larimer County Heath Director, will be joining City Manager Atteberry to provide tonight’s update. Expected topics include: o State variance request o Facial coverings o Northside Aztlan Center o Breweries/Tap Room openings o Restaurant openings o Next steps related to Council’s agenda o Next steps related to boards and commissions It was noted that sheltering activities at Northside have been extended for an additional three weeks and that facial coverings are not expected to go away anytime soon. Ensuring decisions are based on monitoring outcomes and performance is expected. Information from Tom Gonzales related to facial coverings is attached. • City Manager and City Attorney Mid-Year Reviews – It was noted that memos have been received by both the City Manager and City Attorney in preparation for tonight’s discussion. Councilmembers are asked to review the memos in advance of the meeting. June 2 Regular Meeting: The June 2 agenda items were reviewed. • Hybrid Meeting – There was a question about whether the June 2 meeting would be done similar to May 19, with some Councilmembers present in person and allowing all modes of participation. It was noted that the May 19 meeting went well and that getting back to something more normal regarding on-site participation was preferred. The Governor has announced new rules that will allow gatherings of up to 50 people, so this would allow people to be in Council Chambers. Continuing to allow remote Leadership Planning Team Meeting May 26, 2020 Page 2 of 3 participation was encouraged. The City Manager will follow up with individual Councilmembers to discuss this. On a separate note related to Hughes, there was a question about whether staff had heard anything from the Independent Ethics Commission on the complaints that were filed; staff has not. No information is expected to be available until after June 5, at the earliest, and there may be no contacts. • Proclamations – The Mayor will continue to provide summary information about each. • College Avenue/Trilby Intersection Improvements – Staff will begin with construction of a protected left turn as a first step for this project. This may cause some additional short-term congestion; however, is needed to address safety issues. • Fort Fund and Private Activity Bond Allocation Items – Noted as good news items; indicative that important staff work has continued. • COVID-19 Staff Report – Is expected to take 15 minutes and will be focused on small business. • Horsetooth Outlet Project Staff Report – Is expected to take 10 minutes. • Community Development Block Grant (CDBG) Funding – This is a discussion item that reflects the $650K in CDBG COVID funds received through CARES 1.0. A listing of all items suggested for funding will be included in the agenda materials. 6-Month Calendar Continued: • May 28 o Urban Renewal Authority Board – A remote meeting is scheduled for May 28. The only item being considered relates to conducting Board business remotely. • August 25 o Bird Electric Scooter Share Pilot Program Review was added to the calendar. Staff is re- negotiating with Bird and CSU. They are expected to continue to provide service in the community. City Clerk Coldiron: • Reported back on the check-in done with staff liaisons and most City boards and commission are hoping to move forward and start meeting. Staff will bring forward an Ordinance on June 2 to update Ordinance 061, authorizing Council to consider all items (no COVID-19 restriction on items that move forward) and similarly authorizing boards and commissions to meet and consider all items. If approved by Council, it will also authorize boards and commission to meet remotely in full or in part if desired. Leadership Planning Team Meeting May 26, 2020 Page 3 of 3 Deputy City Manager DiMartino: • Noted that Human Resources staff will be available to assist Council with their executive session tonight if needed. City Manager Atteberry: • Attended, along with Mayor Troxell, a Kick-off to Summer Drive In event held by Timberline Church. The broadcast was done from the rooftop of the church and included some worship songs, words from Pastor Dary, and some fun (Simon Says and Trivia). The event was well attended and people were very supportive of City leadership and their efforts. • Noted that the City continues to get many complaints regarding issues in the Library Park Neighborhood. Staff is working hard to address the issues. Mayor Troxell: • Asked about emails now showing “External” in the subject line and whether this could be removed. Staff is asked to follow up. Meeting adjourned at 8:34 a.m. From: Darin Atteberry To: Delynn Coldiron; Wade Troxell; Kristin Stephens; Carrie Daggett; Kelly DiMartino Subject: FW: [EXTERNAL] Face Coverings - An Evidence Review Date: Tuesday, May 26, 2020 7:52:23 AM Attachments: image001.png Face Masks Against COVID19 An Evidence Review (1).pdf 1 of 2 messages from Tom G. . . . . . . . . . . . . . . . . . . . . . . . Darin Atteberry, ICMA-CM / AICP City Manager City of Fort Collins, Colorado 970-221-6505 office datteberry@fcgov.com From: Tom Gonzales <gonzaltr@co.larimer.co.us> Date: Friday, May 22, 2020 at 9:49 AM To: Darin Atteberry <DATTEBERRY@fcgov.com> Subject: [EXTERNAL] Face Coverings - An Evidence Review Hi Darin, Thank you for our conversation today. As promised, here is information regarding the efficacy of face coverings: Face coverings are one part of slowing the spread of the virus. Social distancing is also a key part in keeping COVID-19 cases low in our community. Each business environment is unique. If businesses can prove that they can follow our checklist for social distancing, that provides protection for both customers and employees, face coverings may not be required. We seek to develop creative mechanisms to control the spread of the COVID-19 virus as part of the overall goal of keeping County businesses and citizens safe and as operational as possible. All of these activities together are suppressing the virus in Larimer County. I gave an update to the BoCC yesterday on the good news. We have flattened the curve, but the curve does not go away. https://www.coloradoan.com/story/news/2020/05/12/larimer-county-modify-mask-rules- apply-safer-home-variance/3117017001/ As for the best data and information on the efficacy of face covers, I refer to Face Masks Against COVID-19: An Evidence Review (attached). CDC does recommend the use of cloth face coverings in public settings. Thank you, -Tom -- Larimer County Tom Gonzales, MPH, REHS Public Health Director Health and Environment 1525 Blue Spruce Drive Fort Collins, CO 80524 W: (970) 498-6714 | M: (970) 278-6300 tgonzales@larimer.org | www.larimer.org From: Darin Atteberry To: Delynn Coldiron; Wade Troxell; Kristin Stephens; Carrie Daggett; Kelly DiMartino Subject: FW: [EXTERNAL] Re: Face Coverings - An Evidence Review Date: Tuesday, May 26, 2020 7:53:29 AM Attachments: image001.png 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . Darin Atteberry, ICMA-CM / AICP City Manager City of Fort Collins, Colorado 970-221-6505 office datteberry@fcgov.com From: Tom Gonzales <gonzaltr@co.larimer.co.us> Date: Friday, May 22, 2020 at 10:06 AM To: Darin Atteberry <DATTEBERRY@fcgov.com> Subject: [EXTERNAL] Re: Face Coverings - An Evidence Review Hi Darin, Also, my team has updated our face covering messaging on our website. https://www.larimer.org/health/communicable-disease/coronavirus-covid-19/face-coverings-and- masks On Fri, May 22, 2020 at 9:49 AM Tom Gonzales <gonzaltr@co.larimer.co.us> wrote: Hi Darin, Thank you for our conversation today. As promised, here is information regarding the efficacy of face coverings: Face coverings are one part of slowing the spread of the virus. Social distancing is also a key part in keeping COVID-19 cases low in our community. Each business environment is unique. If businesses can prove that they can follow our checklist for social distancing, that provides protection for both customers and employees, face coverings may not be required. We seek to develop creative mechanisms to control the spread of the COVID-19 virus as part of the overall goal of keeping County businesses and citizens safe and as operational as possible. All of these activities together are suppressing the virus in Larimer County. I gave an update to the BoCC yesterday on the good news. We have flattened the curve, but the curve does not go away. https://www.coloradoan.com/story/news/2020/05/12/larimer-county-modify-mask-rules- apply-safer-home-variance/3117017001/ As for the best data and information on the efficacy of face covers, I refer to Face Masks Against COVID-19: An Evidence Review (attached). CDC does recommend the use of cloth face coverings in public settings. Thank you, -Tom -- Larimer County Tom Gonzales, MPH, REHS Public Health Director Health and Environment 1525 Blue Spruce Drive Fort Collins, CO 80524 W: (970) 498-6714 | M: (970) 278-6300 tgonzales@larimer.org | www.larimer.org -- Larimer County Tom Gonzales, MPH, REHS Public Health Director Health and Environment 1525 Blue Spruce Drive Fort Collins, CO 80524 W: (970) 498-6714 | M: (970) 278-6300 tgonzales@larimer.org | www.larimer.org 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 synthesize the relevant literature to inform multiple areas: 1) transmission characteristics of COVID-19, 2) ﬁltering characteristics and efﬁcacy of masks, 3) esti- mated 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 small res- piratory droplets, and is known to be transmissible from presymp- tomatic and asymptomatic individuals. Reducing disease spread requires two things: ﬁrst, limit contacts of infected individuals via physical distancing and contact tracing with appropriate quarantine, and second, reduce the transmission probability per contact by wear- ing masks in public, among other measures. 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 effec- tive at stopping spread of the virus when compliance is high. The de- creased transmissibility could substantially reduce the death toll and economic impact while the cost of the intervention is low. Thus we recommend the adoption of public cloth mask wearing, as an effec- tive form of source control, in conjunction with existing hygiene, dis- tancing, 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. COVID-19 | SARS-CoV-2 | Masks | Pandemic Policymakers need urgent guidance on the use of masks by the general population as a tool in combating SARS-CoV- 2, the respiratory virus that causes COVID-19. Masks have been recommended as a potential tool to tackle the COVID- 19 pandemic since the initial outbreak in China (1), although usage during the outbreak varied by time and province (2). Globally, countries are grappling with translating the evi- dence of public mask wearing to their contexts. These poli- cies are being developed in a complex decision-making envi- ronment, with a novel pandemic, rapid generation of new re- search, and exponential growth in cases and deaths in many areas. There is currently a global shortage of N95 or FFP2 res- pirators and surgical masks for use in hospitals. Simple cloth masks present a pragmatic solution for use by the public. This has been supported by the United States and European Cen- tres for Disease Control. We present a literature review on the role of simple cloth masks and policies in reducing COVID-19 transmission. 1. Components to Evaluate for Public Mask Wearing In order to identify whether public mask wearing is an appro- priate policy, we need to consider these questions: 1. Do asymptomatic or presymptomatic patients pose a risk of infecting others? 2. Would a face mask likely decrease the number of people infected by an infectious mask wearer? 3. Are there alternative face covers that will not disrupt the medical supply chain, e.g. homemade cloth masks? 4. Will wearing a mask impact the probability of the wearer becoming infected themselves? 5. Does mask use reduce compliance with other recom- mended strategies, such as physical distancing and quar- antine? Signiﬁcance Statement 6. Are there any other potential beneﬁts to universal mask wearing such as reducing stigma, signaling solidarity, and increased compliance with other measures? We will evaluate each consideration in turn. 2. Transmission Characteristics of COVID-19 A primary route of transmission of SARS-CoV-2 is likely via small droplets that are ejected when speaking, coughing or sneezing. The most common droplet size threshold has a min- imum at 5 µm to 10 µm (3, 4). There is much debate about whether these droplets should sometimes be considered an aerosol (5). An added complexity is that aerosols are not consistently deﬁned in the literature. Although earlier studies assumed that droplets were spread mainly through coughing, a more recent analysis has found that transmission through talking may be a key vector, with louder speech creating increasing quantities and sizes of droplets, which are associated with a higher viral load (6). SARS-CoV-2 is highly transmissible, with a replication number estimated to be approximately 2.4 (7) although es- timates vary (8) and will likely change as improved mea- surements of asymptomatic spread become available. Many COVID-19 patients are asymptomatic, and nearly all have a pre-symptomatic incubation period ranging from 2 to 15 days, with a median length of 5.1 days (9). Patients are most infectious during the initial days of infection (10–15), when symptoms are mildest or not present. This characteris- tic diﬀerentiates SARS-CoV-2 (COVID-19) from SARS-CoV, as replication is activated early in the upper respiratory tract (14, 16). High viral titers of SARS-CoV-2 are reported in the saliva of COVID-19 patients. These titers have been highest at time of patient presentation and viral levels are just as high in asymptomatic or presymptomatic patients (11, 16). A consequence of these disease characteristics is that any successful intervention policy must properly address transmis- sion due to infectious patients that display few or no symp- toms and may not realize that they are infected. 3. Filtering Capability of Masks Masks can be made of diﬀerent materials and designs (17) which inﬂuence their ﬁltering capability. There are rigorous standards evaluating masks used in healthcare settings but these focus on personal protective equipment (PPE) eﬃcacy, that is, the ability of the mask to protect the wearer from infectious particles. N95 (the American standard; the equiv- alent in Europe is FFP2) respirators are recommended for health workers conducting aerosol-generating procedures dur- ing clinical care of COVID-19 patients. While it has been shown that N95 or FFP2 respirators perform well as PPE, they can become a scarce resource during a pandemic. Toner and Waldhorn (2006) (18) point out that shortages of N95 or FFP2 respirators should be anticipated, and say that if no other masks are available, surgical masks, which will provide droplet protection, should be used. One approach that has been studied for handling N95 or FFP2 respirator shortages is sterilization and re-use, which can be eﬀective (19). Masks can also be used for source control, which refers to blocking droplets ejected by the wearer, as well as PPE. Al- though we consider both of these as important, our focus in this paper is on source control, because if everyone is wear- ing masks to decrease the chance that they themselves are unknowingly infecting someone, everyone ends up being more 4. Mask Efﬁcacy Studies Although no randomized controlled trials (RCT) on the use of masks as source control for SARS-CoV-2 has been pub- lished, a number of studies have attempted to indirectly esti- mate the eﬃcacy of masks. Overall, an evidence review (29) ﬁnds "moderate certainty evidence shows that the use of hand- washing plus masks probably reduces the spread of respiratory viruses." The most relevant paper (30), with important implications for public mask wearing during the COVID-19 outbreak, is one that compares the eﬃcacy of surgical masks for source con- trol for seasonal coronavirus, inﬂuenza, and rhinovirus. With ten participants, the masks were eﬀective at blocking coron- avirus droplets of all sizes for every subject. However, masks were far less eﬀective at blocking rhinovirus droplets of any size, or of blocking small inﬂuenza droplets. The results sug- gest that masks may have a signiﬁcant role in source control for the current coronavirus outbreak. The study did not use COVID-19 patients, and it is not yet known whether seasonal coronavirus behaves the same as SARS-CoV-2; however, they are of the same genus, so similar behavior is likely. Another relevant (but under-powered, with n=4) study (31) found that a cotton mask blocked 96% (reported as 1.5 log units or about a 36-fold decrease) of viral load on average, at eight inches away from a cough from a patient infected with COVID-19. If this is replicated in larger studies it would be an important result, because it has been shown (32) that "ev- ery 10-fold increase in viral load results in 26% more patient deaths" from "acute infections caused by highly pathogenic viruses". A comparison of homemade and surgical masks for bac- terial and viral aerosols (21) observed that "the median-ﬁt factor of the homemade masks was one-half that of the sur- gical masks. Both masks signiﬁcantly reduced the number of microorganisms expelled by volunteers, although the surgical mask was 3 times more eﬀective in blocking transmission than the homemade mask." Research focused on aerosol exposure has found all types of masks are at least somewhat eﬀective at protecting the wearer. Van der Sande et al (33) found that "all types of masks reduced aerosol exposure, relatively stable over time, unaﬀected by duration of wear or type of activity", and concluded that "any type of general mask use is likely to decrease viral exposure and infection risk on a population level, despite imperfect ﬁt and imperfect adherence". Overall however, analysis of particle ﬁltration is likely to underesti- mate the eﬀectiveness of masks, since the fraction of particles that are emitted as aerosol (vs. droplet) is quite small (26). Analysis of seasonal coronavirus compared to rhinovirus (30) suggests that ﬁltration of COVID-19 may be much more ef- fective, especially for source control. The importance of using masks for health care workers has been observed (34) in three Chinese hospitals where, in each hospital, medical staﬀ wearing masks (mainly in quaran- tine areas) had no COVID-19 infections, despite being around COVID-19 patients far more often, whilst other medical staﬀ had 10 or more infections in each of the three hospitals. Masks seem to be eﬀective for source control in the con- trolled setting of an airplane. One case report (35) describes a man who ﬂew from China to Toronto and then tested posi- tive for COVID-19. He was wearing a mask during the ﬂight. piratory illness being evaluated and what reference standard was used (no mask or surgical mask). There are no RCTs that have been done to evaluate the impact of masks on com- munity transmission during a coronavirus pandemic. While there is some evidence from inﬂuenza outbreaks, the current global pandemic poses a unique challenge. A review (42) of 67 studies including randomized controlled trials and obser- vational studies found that simple and lowcost interventions would be useful for reducing transmission of epidemic respi- ratory viruses. The review recommended that "the following eﬀective interventions should be implemented, preferably in a combined fashion, to reduce transmission of viral respiratory disease: 1. frequent handwashing with or without adjunct antiseptics; 2. barrier measures such as gloves, gowns, and masks with ﬁltration apparatus; and 3. suspicion diagnosis with the isolation of likely cases". However, it cautioned that routine longterm implementation of some measures assessed might be diﬃcult without the threat of an epidemic. Seuess et al conducted an RCT (43)that suggests house- hold transmission of inﬂuenza can be reduced by the use of non-pharmaceutical interventions, namely the use of face masks and intensiﬁed hand hygiene, when implemented early and used diligently. Concerns about acceptability and tolera- bility of the interventions should not be a reason against their recommendation (43). Cowling et al (44) investigated hand hygiene and face masks in an RCT that seemed to prevent household transmission of inﬂuenza virus when implemented within 36 hours of index patient symptom onset. These ﬁnd- ings suggest that non-pharmaceutical interventions are impor- tant for mitigation of pandemic and inter-pandemic inﬂuenza. RCT ﬁndings by Aiello et al (45) "suggest that face masks and hand hygiene may reduce respiratory illnesses in shared living settings and mitigate the impact of the inﬂuenza A (H1N1) pandemic". A randomized intervention trial (46) found that "face masks and hand hygiene combined may re- duce the rate of ILI [inﬂuenza-like illness] and conﬁrmed in- ﬂuenza in community settings. These non-pharmaceutical measures should be recommended in crowded settings at the start of an inﬂuenza pandemic." The authors noted that their study "demonstrated a signiﬁcant association between the combined use of face masks and hand hygiene and a sub- stantially reduced incidence of ILI during a seasonal inﬂuenza outbreak. If masks and hand hygiene have similar impacts on primary incidence of infection with other seasonal and pan- demic strains, particularly in crowded, community settings, then transmission of viruses between persons may be signiﬁ- cantly decreased by these interventions." An observational study in Hong Kong on SARS (47) found "frequent mask use in public venues, frequent hand washing, and disinfecting the living quarters were signiﬁcant protective factors (OR 0.36 to 0.58)". An important observation was that "members of the case group [infected with SARS] were less likely than members of the control group [not infected] to have frequently worn a face mask in public venues (27.9% vs. 58.7%)". B. Implementation and Sociolological Considerations. For a novel disease where much is unknown, it is important to ex- amine the context of studies closely and also distinguish "ab- sence of evidence" from "evidence of absence" (2). We discuss estimates of cloth mask ﬁltering performance in Filtering Ca- infected or people who are taking care of someone infected. However, research shows that many sick people are reluctant to wear a mask if it identiﬁes them as sick, and thus end up not wearing them at all in an eﬀort to avoid the stigma of illness (60, 61). Stigma is a powerful force in human societies, and many illnesses come with stigma for the sick as well as fear of them, and managing the stigma is an important part of the process of controlling epidemics as stigma also leads to people avoiding treatment as well as preventive measures that would "out" their illness (62). Many health authorities have recommended wearing masks for COVID-19 only if people are sick; however, reports of people wearing masks being at- tacked, shunned and stigmatized have already been observed (63). Having masks worn only by the suspected/conﬁrmed infected also has led to employers in high-risk environments like grocery stores and prisons, and even hospitals, banning employees from wearing one sometimes with the idea that it would scare the customer or the patients (64, 65). Further, in many countries, minorities suﬀer additional stigma and as- sumptions of criminality (66). In that vein, black people in the United States have reported that they were reluctant to wear masks in public during this pandemic for fear of being mistaken as criminals (67, 68). Even if it were possible to en- courage only infected people to wear masks, given the lack of access to testing in many countries, it is not possible for many people to know for sure if they are infected or not (69). Thus, while this paper has shown the importance of masks for source- control – preventing asymptomatic and presymptomatic peo- ple from infecting others – it may not even be possible to have infected/sick people wear masks due to stigma, employer re- strictions, or simple lack of knowledge of ones status without mask-wearing becoming universal policy. Another important beneﬁt of recommending universal mask wearing would be to serve as a visible signal and re- minder of the pandemic, and given the importance of ritual and solidarity in human societies (70), it is plausible that visible, public signaling via mask wearing can potentially in- crease compliance with other health measures as well, such as keeping distance and hand-washing. Health, especially during an epidemic, is a form of public good in that everyone else’s health behaviors improve the health odds of everyone else, and that it is non-rivalrous in that one person’s health does not di- minish the health of anyone else (71, 72). Visible signals play an important role in human societies (73). As such, signaling participation in health behaviors by wearing a mask as well as visible enforcement (for example, shops asking customers to wear masks) can increase compliance (74). Further, histor- ically epidemics are a time of fear, confusion and helplessness (75, 76). Mask-wearing and even mask-making or distribution can provide feelings of empowerment and self-eﬃcacy (77), which would in turn also suggest masks could increase com- pliance in other health-behaviors as well by increasing self- eﬃcacy. In Hong Kong, for example, a community-driven focus on epidemic prevention started in the early days of COVID-19, and included community activists acquiring and distributing masks especially to those without resources and the elderly, even before it was oﬃcially declared a pandemic or before their own government had taken strong steps (78). Currently, Hong Kong has not only a relatively contained epi- demic compared with many other countries, but a signiﬁcant Fig. 1. Impact of public mask wearing under the full range of mask adherence and efﬁcacy scenarios. The color indicates the resulting reproduction number R0 from an initial R0 of 2.4 (7). the number of cases infected by one case,in a completely sus- ceptible population. R0 determines the rate of growth, with a superlinear eﬀect. The goal of any related healthcare policy is to have an aggregate eﬀect of reducing R0 to below 1.0. Eﬃcacy of face masks within local interventions would have an aggregate eﬀect on the reproduction number of the epidemic. What is the magnitude of such an eﬀect? The HKBU COVID-19 Modelling Group developed a transmission model that incorporated mask wearing and mask eﬃcacy as a factor in the model (89). They estimate reductions in the basic reproduction number R0 under common intervention measures. For wearing masks, they ﬁnd that wearing masks reduces R0 by a factor (1 − epm)2 , where e is the eﬃcacy of trapping viral particles inside the mask, and pm is the per- centage of the population that wears masks. When combined with contact tracing, the two eﬀects multiply. A conservative assessment applied to the COVID-19 esti- mated R0 of 2.4 (7) might posit 50% mask usage and a 50% mask eﬃcacy level, reducing R0 to 1.35, an order of magnitude impact rendering spread comparable to the reproduction num- ber of seasonal inﬂuenza. To put this in perspective, 100 cases at the start of a month becomes 31,280 cases by the month’s end (R0 = 2.4) vs. only 584 cases (R0 = 1.35). Such a slow- down in case-load protects healthcare capacity and renders a local epidemic amenable to contact tracing interventions that can eliminate the spread entirely. A full range of eﬃcacy e and adherence pm is shown with the resulting R0 in Figure 1, illustrating regimes in which growth is halted entirely (R0 < 1) as well as pessimistic regimes (e.g. due to poor implementation or population com- pliance) that nonetheless result in a beneﬁcial eﬀect in sup- pressing the exponential growth of the pandemic. Yan et al (90) provide an additional example of an incre- mental impact assessment of respiratory protective devices using an augmented variant of a traditional SIR model in the context of inﬂuenza with N95 respirators. They showed that a suﬃciently high adherence rate (~ 80% of the population) resulted in the elimination of the outbreak with most respira- tory protective devices. Qualitative comparisons of outcomes between countries (91, 92) are suggestive of policy diﬀerences leading to diﬀer- ences in disease spread of up to three orders of magnitude. Al- though between-country comparisons do not allow for causal attribution, they suggest mask wearing to be a low-risk mea- sure with a potentially large positive impact, with many coun- tries with widespread use of masks in public keeping deaths below one in a million. Abaluck et al (93) extend the between-country analyses from a cost perspective, estimating the marginal beneﬁt per cloth mask worn to range from $3,000-$6,000. They also found that "the average daily growth rate of conﬁrmed posi- tives is 18% in countries with no preexisting mask norms and 10% in countries with such norms." and "that the growth rate of deaths is 21% in countries with no mask norms and 11% in countries with such norms." 6. Discussion and Recommendations modest beneﬁts can be massively beneﬁcial in the aggregate due to the exponential character of the transmission process. Therefore, the action of ensuring widespread use of masks in the community should be taken, based on this principle (95). Models suggest that public mask wearing is most eﬀective at stopping spread of the virus when compliance is high. This is the same situation as we see with vaccines - the more peo- ple are vaccinated, the higher the beneﬁt to the whole popu- lation including those who cannot be vaccinated like infants or immuno-compromised people. A common policy response to this conundrum is to ensure compliance by using laws and regulations, such as widespread state laws in the US which re- quire vaccinations to attend school. Research shows that the strength of the mandate to vaccinate greatly inﬂuences compli- ance rates for vaccines and that policies that set a higher bar for vaccine exemptions result in higher vaccination rates. (96) The same approach is now being used in many jurisdictions to increase mask wearing compliance, by mandating mask use in a variety of settings (such as public transportation or gro- cery stores or even at all times outside the home). Early results suggest that these laws are eﬀective at increasing com- pliance and slowing or stopping the spread of COVID-19 (91). We recommend that mask use requirements are implemented by governments, or when governments do not, by organiza- tions that provide public-facing services, such as transit ser- vice providers or stores, as "no mask, no service" rules. Such mandates must be accompanied by measures to ensure access to masks, possibly including distribution and rationing mech- anisms so that they do not become discriminatory but remain focused on the public health beneﬁt. Given the value of the source control principle, especially for presymptomatic peo- ple, it is not good enough for only employees to wear masks, customers must wear masks as well. It is also important for health authorities to provide clear guidelines for the production, use and sanitization or re-use of face masks, and consider their distribution as shortages allow. A number of countries have distributed surgical masks (South Korea, Taiwan) from early on while Japan and Singapore are now distributing cloth masks to their whole population. Clear and implementable guidelines can help increase compliance, and bring communities closer to the goal of reducing and ul- timately stopping the spread of COVID-19. Materials and Methods A community-driven approach was used for building the paper list used in this literature review. A multidisciplinary community of researchers used online tools to review and actively discuss publi- cations related to the question of the eﬀectiveness and policy of public mask wearing. ACKNOWLEDGMENTS. Thank you to Sylvain Gugger for LATE X help, and to Cam Woodsum for assistance with preparing bibtex citations. References 1. Q Wang, C Yu, Letter to editor: Role of masks/respirator protection against 2019-novel coro- navirus (COVID-19). Infect. Control. & Hosp. Epidemiol., 1–7 (year?). 2. S Feng, et al., Rational use of face masks in the COVID-19 pandemic. The Lancet Respir. Medicine 0 (2020). 3. J Duguid, The size and the duration of air-carriage of respiratory droplets and droplet-nuclei. Epidemiol. & Infect. 44, 471–479 (1946). 4. L Morawska, et al., Size distribution and sites of origin of droplets expelled from the human adults: a randomized intervention trial. The J. Infect. Dis. 201, 491–498 (2010). 46. AE Aiello, et al., Facemasks, Hand Hygiene, and Inﬂuenza among Young Adults: A Random- ized Intervention Trial. PLoS ONE 7 (2012). 47. JT Lau, H Tsui, M Lau, X Yang, SARS Transmission, Risk Factors, and Prevention in Hong Kong. Emerg. Infect. Dis. 10, 587–592 (2004). 48. The Lancet, COVID-19: protecting health-care workers. The Lancet 395, 922 (2020). 49. LM Brosseau, ScD, M Sietsema, P| Apr 01, 2020, COMMENTARY: Masks-for-all for COVID- 19 not based on sound data (2020). 50. MM Cassell, DT Halperin, JD Shelton, D Stanton, Risk compensation: the achilles’ heel of innovations in hiv prevention? Bmj 332, 605–607 (2006). 51. D Rojas Castro, RM Delabre, JM Molina, Give prep a chance: moving on from the risk com- pensation concept. J. Int. AIDS Soc. 22, e25351 (2019). 52. JV Ouellet, Helmet use and risk compensation in motorcycle accidents. Trafﬁc injury preven- tion 12, 71–81 (2011). 53. DJ Houston, LE Richardson, Risk compensation or risk reduction? seatbelts, state laws, and trafﬁc fatalities. Soc. Sci. Q. 88, 913–936 (2007). 54. Y Peng, et al., Universal motorcycle helmet laws to reduce injuries: a community guide sys- tematic review. Am. journal preventive medicine 52, 820–832 (2017). 55. MD Scott, et al., Testing the risk compensation hypothesis for safety helmets in alpine skiing and snowboarding. Inj. Prev. 13, 173–177 (2007). 56. G Ruedl, M Kopp, M Burtscher, Does risk compensation undo the protection of ski helmet use? Epidemiology 23, 936–937 (2012). 57. B Pless, Risk compensation: Revisited and rebutted. Safety 2, 16 (2016). 58. A Burgess, M Horii, Risk, ritual and health responsibilisation: Japans safety blanketof surgical face mask-wearing. Sociol. health & illness 34, 1184–1198 (2012). 59. BJ Condon, T Sinha, Who is that masked person: the use of face masks on mexico city public transportation during the inﬂuenza a (h1n1) outbreak. Heal. Policy 95, 50–56 (2010). 60. K Abney, containing tuberculosis, perpetuating stigma: the materiality of n95 respirator masks. Anthropol. South. Afr. 41, 270–283 (2018). 61. E Buregyeya, et al., Acceptability of masking and patient separation to control nosocomial tuberculosis in uganda: a qualitative study. J. Public Heal. 20, 599–606 (2012). 62. G Joachim, S Acorn, Stigma of visible and invisible chronic conditions. J. advanced nursing 32, 243–248 (2000). 63. DK Li, R Abdelkader, Coronavirus hate attack: Woman in face mask allegedly assaulted by man who calls her ’diseased’. NBC News (2020). 64. Tampa Bay nurses were told not to wear masks in hallways. Now hospitals are changing the rules. (2020) [Online; accessed 9. Apr. 2020]. 65. S Malone, NY Correctional Ofﬁcers Ordered Not To Wear Masks, Even If They Have Them. Maven (2020). 66. D Pager, H Shepherd, The sociology of discrimination: Racial discrimination in employment, housing, credit, and consumer markets. Annu. Rev. Sociol 34, 181–209 (2008). 67. C Fernando Alfonso Iii, Why some people of color say they won’t wear homemade masks (2020) [Online; accessed 9. Apr. 2020]. 68. T Jan, Two black men say they were kicked out of Walmart for wearing protective masks. Others worry it will happen to them. Wash. Post (2020). 69. K Wells, Why cant I get tested? Atlantic (2020). 70. RE Watson-Jones, CH Legare, The social functions of group rituals. Curr. Dir. Psychol. Sci. 25, 42–46 (2016). 71. P Illingworth, WE Parmet, Solidarity and health: A public goods justiﬁcation. Diametros 43, 65–71 (2015). 72. LC Chen, TG Evans, RA Cash, , et al., Health as a global public good. Glob. public goods, 284–304 (1999). 73. R BliegeBird, et al., Signaling theory, strategic interaction, and symbolic capital. Curr. anthro- pology 46, 221–248 (2005). 74. R Van Houten, L Malenfant, B Huitema, R Blomberg, Effects of high-visibility enforcement on driver compliance with pedestrian yield right-of-way laws. Transp. research record 2393, 41–49 (2013). 75. W Van Damme, W Van Lerberghe, Editorial: Epidemics and fear. Trop. Med. Int. Heal. 5, 511–514 (2000). 76. MA Riva, M Benedetti, G Cesana, Pandemic fear and literature: observations from jack lon- dons the scarlet plague. Emerg. infectious diseases 20, 1753 (2014). 77. E Taal, JJ Rasker, ER Seydel, O Wiegman, Health status, adherence with health recom- mendations, self-efﬁcacy and social support in patients with rheumatoid arthritis. Patient education counseling 20, 63–76 (1993). 78. Coronavirus can travel twice as far as ofﬁcial ‘safe distance’, study says (2020) [Online; ac- cessed 10. Apr. 2020]. 79. CC Leung, TH Lam, KK Cheng, Mass masking in the COVID-19 epidemic: people need guidance. The Lancet 395, 945 (2020). 80. J Lyons, To curb the coronavirus, hong kong tells the world masks work; city embraces widespread use of face coverings alongside other measures to slow spread of disease (2020). 81. N Liu, Hong kongs coronavirus response leads to sharp drop in ﬂu cases. FT.com (2020) Name - University of Hong Kong; Chinese University of Hong Kong; Copyright - Copyright The Financial Times Limited Mar 5, 2020; Last updated - 2020-03-23; SubjectsTermNotLit- GenreText - China; Hong Kong. 82. BJ Cowling, et al., Impact assessment of non-pharmaceutical interventions against COVID- 19 and inﬂuenza in Hong Kong: an observational study. medRxiv (2020). 83. GM Leung, et al., A tale of two cities: community psychobehavioral surveillance and related impact on outbreak control in hong kong and singapore during the severe acute respiratory syndrome epidemic. Infect. Control. & Hosp. Epidemiol. 25, 1033–1041 (2004). 84. BJ Cowling, et al., Community psychological and behavioral responses through the ﬁrst wave of the 2009 inﬂuenza a (h1n1) pandemic in hong kong. The J. infectious diseases 202, 867– 876 (2010). 85. World Health Organization (WHO), Global Tuberculosis Report 2019, (World Health Organi- zation, Geneva), Technical report (2019). 86. AS Dharmadhikari, et al., Surgical face masks worn by patients with multidrug-resistant tu- berculosis: impact on infectivity of air on a hospital ward. Am. journal respiratory critical care medicine 185, 1104–1109 (2012). 87. EL Larson, et al., Impact of Non-Pharmaceutical Interventions on URIs and Inﬂuenza in Crowded, Urban Households. Public Heal. Reports 125, 178–191 (2010). 88. CR MacIntyre, et al., The First Randomized, Controlled Clinical Trial of Mask Use in House- holds to Prevent Respiratory Virus Transmission. Int. J. Infect. Dis. 12, e328 (2008). 89. L Tian, et al., Calibrated intervention and containment of the covid-19 pandemic (2020). 90. J Yan, S Guha, P Hariharan, M Myers, Modeling the Effectiveness of Respiratory Protective Devices in Reducing Inﬂuenza Outbreak. Risk Analysis 39, 647–661 (2019). 91. C Lefﬂer, E Ing, CA McKeown, D Pratt, A Grzybowski, Country-wide Mortality from the Novel Coronavirus (COVID-19) Pandemic and Notes Regarding Mask Usage by the Public, Techni- cal report (2020). 92. C Kenyon, Widespread use of face masks in public may slow the spread of SARS CoV-2: an ecological study. medRxiv, 2020.03.31.20048652 (2020). 93. J Abaluck, et al., The Case for Universal Cloth Mask Adoption and Policies to Increase Supply of Medical Masks for Health Workers, (Social Science Research Network, Rochester, NY), SSRN Scholarly Paper ID 3567438 (2020). 94. WC on the Ethics of Scientiﬁc Knowledge, Technology, The precautionary principle (2005). 95. T Greenhalgh, MB Schmid, T Czypionka, D Bassler, L Gruer, Face masks for the public during the covid-19 crisis. BMJ 369 (2020). 96. WD Bradford, A Mandich, Some state vaccination laws contribute to greater exemption rates and disease outbreaks in the united states. Heal. Aff. 34, 1383–1390 (2015). 8 Howard et al. Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 12 April 2020 doi:10.20944/preprints202004.0203.v1 respiratory tract during expiratory activities. J. Aerosol Sci. 40, 256–269 (2009). 5. L Bourouiba, Turbulent Gas Clouds and Respiratory Pathogen Emissions: Potential Implica- tions for Reducing Transmission of COVID-19. JAMA (2020). 6. P Anﬁnrud, CE Bax, V Stadnytskyi, A Bax, Could sars-cov-2 be transmitted via speech droplets? medRxiv (2020). 7. N Ferguson, et al., Report 9: Impact of non-pharmaceutical interventions (npis) to reduce covid19 mortality and healthcare demand (2020). 8. Y Liu, AA Gayle, A Wilder-Smith, J Rocklöv, The reproductive number of covid-19 is higher compared to sars coronavirus. J. travel medicine (2020). 9. SA Lauer, et al., The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Pub- licly Reported Conﬁrmed Cases: Estimation and Application. Annals Intern. Medicine (2020). 10. KKW To, et al., Temporal proﬁles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study. Lancet Infect. Dis. 0 (2020). 11. L Zou, et al., SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. New Engl. J. Medicine 382, 1177–1179 (2020). 12. Y Bai, et al., Presumed asymptomatic carrier transmission of covid-19. Jama (2020). 13. J Zhang, et al., Evolving epidemiology and transmission dynamics of coronavirus disease 2019 outside Hubei province, China: a descriptive and modelling study. The Lancet Infect. Dis. 0 (2020). 14. N van Doremalen, et al., Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. New Engl. J. Medicine 0, null (2020). 15. WE Wei, Presymptomatic Transmission of SARS-CoV-2 â Singapore, January 23âMarch 16, 2020. MMWR. Morb. Mortal. Wkly. Rep. 69 (2020). 16. R Wölfel, et al., Virological assessment of hospitalized patients with covid-2019. Nature, 1–10 (2020). 17. Brosseau, N95 Respirators and Surgical Masks | | Blogs | CDC (2009). 18. E Toner, R Waldhorn, What Hospitals Should Do to Prepare for the Inﬂuenza Pandemic. Mary Ann Liebert Inc. 4, 397–402 (2006). 19. P de Man, et al., Sterilization of disposable face masks by means of standardized dry and steam sterilization processes: an alternative in the ﬁght against mask shortages due to COVID-19 (2020). 20. S Asadi, et al., Aerosol emission and superemission during human speech increase with voice loudness. Sci. reports 9, 1–10 (2019). 21. A Davies, et al., Testing the Efﬁcacy of Homemade Masks: Would They Protect in an In- ﬂuenza Pandemic? Disaster Medicine Public Heal. Prep. 7, 413–418 (2013). 22. S Rengasamy, B Eimer, RE Shaffer, Simple Respiratory ProtectionEvaluation of the Filtration Performance of Cloth Masks and Common Fabric Materials Against 201000 nm Size Particles. The Annals Occup. Hyg. 54, 789–798 (2010). 23. Mvd Sande, P Teunis, R Sabel, Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population. PLOS ONE 3, e2618 (2008). 24. VM Dato, D Hostler, ME Hahn, Simple Respiratory Mask. Emerg. Infect. Dis. 12, 1033–1034 (2006). 25. DK Milton, MP Fabian, BJ Cowling, ML Grantham, JJ McDevitt, Inﬂuenza Virus Aerosols in Human Exhaled Breath: Particle Size, Culturability, and Effect of Surgical Masks. PLOS Pathog. 9, e1003205 (2013). 26. RS Papineni, FS Rosenthal, The size distribution of droplets in the exhaled breath of healthy human subjects. J. Aerosol Medicine 10, 105–116 (1997). 27. DIY Face Mask – 8 Steps in Making Protective Gear | Consumer Council (2020) [Online; accessed 8. Apr. 2020]. 28. Coronavirus Disease 2019 (COVID-19) (2020) [Online; accessed 8. Apr. 2020]. 29. J Burch, C Bunt, Can physical interventions help reduce the spread of respiratory viruses? Cochrane Clin. Answers (2020). 30. NH Leung, et al., Respiratory virus shedding in exhaled breath and efﬁcacy of face masks. Nat. Medicine, 1–5 (2020). 31. S Bae, et al., Effectiveness of Surgical and Cotton Masks in Blocking SARSCoV-2: A Con- trolled Comparison in 4 Patients. Annals Intern. Medicine (2020). 32. SC Jiang, et al., Every 10-fold increase in viral load results in 26% more patient deaths: a correlation analysis. Int J Clin Exp Med 12, 13712–13722 (2019). 33. M van der Sande, P Teunis, R Sabel, Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population. PLoS ONE 3 (2008). 34. X Wang, Z Pan, Z Cheng, Association between 2019-nCoV transmission and N95 respirator use. J. Hosp. Infect. 0 (2020). 35. KL Schwartz, et al., Lack of COVID-19 Transmission on an International Flight. CMAJ (2020). 36. L Zhang, et al., Protection by Face Masks against Inﬂuenza A(H1N1)pdm09 Virus on Trans- Paciﬁc Passenger Aircraft, 2009. Emerg. Infect. Dis. 19, 1403–1410 (2013). 37. AR Wilkes, JE Benbough, SE Speight, M Harmer, The bacterial and viral ﬁltration perfor- mance of breathing system ﬁlters*. Anaesthesia 55, 458–465 (2000). 38. Y Long, et al., Effectiveness of N95 respirators versus surgical masks against inﬂuenza: A systematic review and meta-analysis. J. Evidence-Based Medicine n/a (2020). 39. DF Johnson, JD Druce, C Birch, ML Grayson, A quantitative assessment of the efﬁcacy of surgical and N95 masks to ﬁlter inﬂuenza virus in patients with acute inﬂuenza infection. Clin. Infect. Dis. An Off. Publ. Infect. Dis. Soc. Am. 49, 275–277 (2009). 40. LJ Radonovich, et al., N95 Respirators vs Medical Masks for Preventing Inﬂuenza Among Health Care Personnel: A Randomized Clinical Trial. JAMA 322, 824–833 (2019). 41. CR MacIntyre, et al., A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ Open 5, e006577 (2015). 42. T Jefferson, et al., Physical interventions to interrupt or reduce the spread of respiratory viruses. The Cochrane Database Syst. Rev. 2011 (2011). 43. T Suess, et al., The role of facemasks and hand hygiene in the prevention of inﬂuenza trans- mission in households: results from a cluster randomised trial; Berlin, Germany, 2009-2011. BMC infectious diseases 12, 26 (2012). 44. BJ Cowling, et al., Facemasks and hand hygiene to prevent inﬂuenza transmission in house- holds: a cluster randomized trial. Annals Intern. Medicine 151, 437–446 (2009). 45. AE Aiello, et al., Mask use, hand hygiene, and seasonal inﬂuenza-like illness among young Howard et al. 7 Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 12 April 2020 doi:10.20944/preprints202004.0203.v1 Our review of the literature oﬀers evidence in favor of widespread mask use to reduce community transmission: non- medical masks use materials that obstruct droplets of the nec- essary size; people are most infectious in the initial period post-infection, where it is common to have few or no symp- toms (10–16); non-medical masks have been eﬀective in reduc- ing transmission of inﬂuenza; non-medical masks have been shown to be eﬀective in small trials at blocking transmission of coronavirus; and places and time periods where mask us- age is required or widespread have shown substantially lower community transmission. The available evidence suggests that near-universal adop- tion of non-medical masks when out in public, in combination with complementary public health measures could successfully reduce eﬀective-R to below 1.0, thereby stopping community spread. Economic analysis suggests that the impact of mask wearing could be thousands of US dollars saved per person per mask (93). Interventions to reduce COVID-19 spread should be priori- tized in order of their expected multiple on eﬀective R divided by their cost. By this criterion experimentation with and deployment of universal masks look particularly promising. When used in conjunction with widespread testing, contact tracing, quarantining of anyone that may be infected, hand washing, and physical distancing, face masks are a valuable tool to reduce community transmission. All of these mea- sures, through their eﬀect on R0, have the potential to reduce the period of lockdown required. As governments talk about relaxing lockdowns, keeping transmissions low enough to pre- serve health care capacity will be critical until a vaccine can be developed. Mask wearing may be critical to preventing a second wave of infections from overwhelming the health care system – further research is urgently needed here. UNESCO states that "when human activities may lead to morally unacceptable harm that is scientiﬁcally plausible but uncertain, actions shall be taken to avoid or diminish that harm" (94). This is known as the "precautionary principle". The World Charter for Nature, which was adopted by the UN General Assembly in 1982, was the ﬁrst international endorse- ment of the precautionary principle. It was implemented in an international treaty in the 1987 Montreal Protocol. The loss of life and economic destruction that has been seen already from COVID-19 is a "morally unacceptable harm". The pos- itive impact of public mask wearing on this is "scientiﬁcally plausible but uncertain". This notion is reﬂected in Figure 1 - while researchers may reasonably disagree on the magni- tude of transmissibility reduction and compliance, seemingly 6 Howard et al. Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 12 April 2020 doi:10.20944/preprints202004.0203.v1 reduction in inﬂuenza cases as well which their health authori- ties attribute, among other factors, to the near-universal mask wearing and strong norms around it (79–81). C. Universal or near-universal mask wearing. Estimating ad- herence to regulations for public mask wearing is a key input for modeling the impact of public mask wearing. Telephone surveys during the SARS-CoV-2 outbreak in Hong Kong re- ported enhanced adherence to public mask wearing as the pan- demic progressed over three weeks, with 74.5% self reported mask wearing when going out increasing to 97.5%, without mandatory requirements (82). Similar surveys reported face mask use in Hong Kong during the SARS outbreak in 2003 as 79% (83), and approximately 10% during the inﬂuenza A(H1N1) pandemic in 2009 (84). This suggests that the pub- lic have enhanced awareness of their risk, and display higher adherence levels to prevention strategies than during other epidemics. Cloth masks could be an additional tool to en- hance awareness of the importance of physical distancing in public places, serving as a visual reminder. Should masks be reserved solely for use in symptomatic patients, they become a symbol of illness and could lead to public stigmatization that discourages use, as has been described for patients with tu- berculosis (61). Countries like the Czech Republic and Hong Kong oﬀer interesting perspectives on the role of citizen ad- vocacy and on the acceptability of face-covering in public. D. Balancing potential harm of cloth masks with additional beneﬁts for concurrent epidemic. Based on our detailed dis- cussion above, cloth masks have not been shown to increase the risk of infection in people using them compared to not wearing any mask. While the focus of this article has been on preventing the spread of COVID-19 disease through public mask wearing, many low-middle income countries face concur- rent epidemics of diseases like tuberculosis. Tuberculosis kills 1.5 million people globally per year, and in 2018, 10 million people fell ill (85). Face covering has been shown to also re- duce the transmission of tuberculosis (86) and oﬀer additional beneﬁts to public mask wearing. Similarly, inﬂuenza transmis- sibility in the community was found to have declined by 44% in Hong Kong after the implementation of changes in pop- ulation behaviors, including social distancing and increased mask wearing, enforced in most stores, during the COVID-19 outbreak (82). It has been noted (87) that ensuring compliance with non- pharmaceutical interventions can be challenging: "Mask wear- ing is a promising non-pharmaceutical intervention to reduce risk of secondary transmission of viral URI [upper respiratory infections], but it is likely that adherence to mask wearing would occur only if there was a major pandemic that resulted in a heightened level of community concern and fear." Many regions have now passed laws to ensure compliance. The ﬁrst RCT (2008) on mask use (88) "found compliance to be low, but compliance is aﬀected by the perception of risk. In a pan- demic, we would expect compliance to improve." The authors noted that "in compliant users, masks were highly eﬃcacious." 5. Estimating Population Impacts At the national and global scale, eﬀective local interventions are aggregated into epidemiological parameters of disease spread. The standard epidemiological measure of spread is known as the reproduction number R0 which parameterizes Howard et al. 5 Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 12 April 2020 doi:10.20944/preprints202004.0203.v1 pability of Masks and summarize modelling on population impact in Estimating Population Impacts. Some of the concerns about public mask wearing have not been around primary evidence for the eﬃcacy of source con- trol, but concerns about how they will be used. We present some considerations for the translation of evidence about pub- lic mask wearing to diverse countries across the globe, outside of the parameters of a controlled research setting: B.1. Supply chain management of N95 respirators and surgical masks. There has been a global shortage of protective equip- ment for health workers, with health workers falling ill and dy- ing of occupationally acquired COVID-19 disease (48). Public messaging encouraging mask use and depleting critical sup- plies have been a major concern. Some regions, like South Korea and Taiwan, have decided to promote surgical mask use on a mass scale and opted to address potential stock issues through rapidly increasing production of surgical masks. In regions where surgical mask supplies are scarce, cloth masks may be a pragmatic temporary alternative to surgical masks for the public. B.2. Sociological considerations and anticipating population-level behavior changes. It is diﬃcult to predict the behavior change that would accompany regulations encouraging public mask use. One concern around public health messaging promot- ing the use of face-covering has been that members of the public may use risk compensation behavior and neglect phys- ical distancing based on overvaluing the protection a surgical mask may oﬀer due to an exaggerated or false sense of se- curity (49). Similar arguments have previously been made for HIV prevention strategies (50) (51) and other safety de- vices and mandates such as motorcycle helmet laws (52) and seat-belts (53). However, research on these topics ﬁnds no such increase in adverse outcomes at the population level but rather improvements in safety and well-being, suggesting that even if risk compensation occurs in some individuals, that ef- fect is dwarfed by the increased safety at the population level (53, 54). Further, even for deliberately high-risk recreational activities such as alpine skiing and snowboarding, wearing a helmet was generally associated with risk reduction oriented- behavior (55), suggesting safety devices are both compatible with and perhaps encourage safety-oriented behavior. Even for high-risk recreational activities like alpine skiing and snow- boarding, helmet use has greatly reduced injury rates (56). In general, various forms of risk compensation theories have been proposed for many diﬀerent safety innovations, but have been not found to have empirical support (57) at the pop- ulation level. These ﬁndings strongly suggest that, instead of withholding a preventative tool, accompanying it with accu- rate messaging that combines diﬀerent preventative measures would display trust in the general public’s ability to act re- sponsibly and empower citizens, and risk compensation is un- likely to undo the positive beneﬁts at the population level (58). At the height of the 2009 inﬂuenza epidemic in Mexico City it was found (59) that mandatory mask requirements in- creased compliance compared to voluntary recommendations. Voluntary compliance was strongly inﬂuenced by public per- ception regarding the eﬀectiveness of the recommended mea- sures. For many infectious diseases, including, for example, tuber- culosis, health authorities recommend masks only for those 4 Howard et al. Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 12 April 2020 doi:10.20944/preprints202004.0203.v1 The 25 people closest to him on plane/ﬂight attendants were tested and all were negative. Nobody has been reported from that ﬂight as getting COVID-19. Another case study involv- ing a masked inﬂuenza patient on an airplane (36) found that "wearing a face mask was associated with a decreased risk for inﬂuenza acquisition during this long-duration ﬂight". Guideline development for health worker personal protec- tive equipment have focused on whether surgical masks or N95 respirators should be recommended. Most of the re- search in this area focuses on inﬂuenza. At this point, it is not known to what extent ﬁndings from inﬂuenza studies apply to COVID-19 ﬁltration. Wilkes et al (37) found that "ﬁltration performance of pleated hydrophobic membrane ﬁl- ters was demonstrated to be markedly greater than that of electrostatic ﬁlters." However, even substantial diﬀerences in materials and construction do not seem to impact the trans- mission of droplet-borne viruses in practice, such as a meta- analysis of N95 respirators compared to surgical masks (38) that found "the use of N95 respirators compared with sur- gical masks is not associated with a lower risk of laboratory- conﬁrmed inﬂuenza." Johnson et al (39) showed that "surgical and N95 masks were equally eﬀective in preventing the spread of PCR-detectable inﬂuenza". Radonovich et al (40) found in an outpatient setting that "use of N95 respirators, compared with medical masks... resulted in no signiﬁcant diﬀerence in the rates of laboratory-conﬁrmed inﬂuenza." One of the most frequently mentioned papers evaluating the beneﬁts and harms of cloth masks have been by MacIntyre et al (41). Findings have been misinterpreted, and therefore justify detailed discussion here. The authors "caution against the use of cloth masks" for healthcare professionals compared to the use of surgical masks and regular procedures, based on an analysis of transmission in hospitals in Hanoi. We empha- size the setting of the study - health workers using masks to protect themselves against infection. The study compared a "surgical mask" group which received 2 new masks per day, to a "cloth mask" group that received 5 masks for the entire 4 week period and were required to wear the masks all day, to a "control group" which used masks in compliance with exist- ing hospital protocols, which the authors describe as a "very high level of mask use". It is important to note that the au- thors did not have a "no mask" control group because it was deemed "unethical to ask participants to not wear a mask." The study does not inform policy pertaining to public mask wearing as compared to the absence of masks in a community setting, since there is not a "no mask" group. The results of the study show that the group with a regular supply of new surgical masks each day had signiﬁcantly lower infection of rhinovirus than the group that wore a limited supply of cloth masks. This paper lends support to the use of clean, surgical masks by medical staﬀ in hospital settings to avoid rhinovirus infection by the wearer, and is consistent with other studies that show cloth masks provide poor ﬁltration for rhinovirus (30). Its implementation does not inform the eﬀect of using cloth masks versus not using masks in a community setting for source control of SARS-CoV-2, which is of the same genus as seasonal coronavirus, which has been found to be eﬀectively ﬁltered by cloth masks in a source control setting (30). A. Studies of Impact on Community Transmission. When evaluating the available evidence for the impact of masks on community transmission, it is critical to clarify the setting of the research study (health care facility or community), the res- Howard et al. 3 Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 12 April 2020 doi:10.20944/preprints202004.0203.v1 protected. Multiple studies show the ﬁltration eﬀects of cloth masks relative to surgical masks. Particle sizes for speech are on the order of 1 µm (20) while typical deﬁnitions of droplet size are 5 µm-10 µm (5). Generally available household materials had between a 49% and 86% ﬁltration rate for 0.02 µm exhaled par- ticles whereas surgical masks ﬁltered 89% of those particles (21). In a laboratory setting, household materials had 3% to 60% ﬁltration rate for particles in the relevant size range, ﬁnd- ing them comparable to some surgical masks (22). In another laboratory setup, a tea cloth mask was found to ﬁlter 60% of particles between 0.02 µm to 1 µm, where surgical masks ﬁl- tered 75% (23). Dato et al (2006) (24), note that "quality com- mercial masks are not always accessible." They designed and tested a mask made from heavyweight T-shirts, ﬁnding that it "oﬀered substantial protection from the challenge aerosol and showed good ﬁt with minimal leakage".Although cloth and surgical masks are primarily targeted towards droplet parti- cles, some evidence suggests they may have a partial eﬀect in reducing viral aerosol shedding (25). When considering the relevance of these studies of ingress, it’s important to note that they are likely to substantially un- derestimate eﬀectiveness of masks for source control. When someone is breathing, speaking, or coughing, only a tiny amount of what is coming out of their mouths is already in aerosol form. Nearly all of what is being emitted is droplets. Many of these droplets will then evaporate and turn into aerosolized particles that are 3 to 5-fold smaller. The point of wearing a mask as source control is largely to stop this pro- cess from occurring, since big droplets dehydrate to smaller aerosol particles that can ﬂoat for longer in air (26). Anﬁnrud et al (6) used laser light-scattering to sensitively detect droplet emission while speaking. Their analysis showed that virtually no droplets were "expelled" with a homemade mask consisting of a washcloth attached with two rubber bands around the head, while signiﬁcant levels were expelled without a mask. The authors stated that "wearing any kind of cloth mouth cover in public by every person, as well as strict adherence to distancing and handwashing, could signiﬁ- cantly decrease the transmission rate and thereby contain the pandemic until a vaccine becomes available." An important focus of analysis for public mask wearing is droplet source control. This refers to the eﬀectiveness of blocking droplets from an infectious person, particularly dur- ing speech, when droplets are expelled at a lower pressure and are not small enough to squeeze through the weave of a cotton mask. Many recommended cloth mask designs also include a layer of paper towel or coﬀee ﬁlter, which could increase ﬁlter eﬀectiveness for PPE, but does not appear to be necessary for blocking droplet emission (6, 27, 28). In summary, there is laboratory-based evidence that house- hold masks have some ﬁltration capacity in the relevant droplet size range, as well some eﬃcacy in blocking droplets and particles from the wearer (26). That is, these masks help people keep their droplets to themselves. 2 Howard et al. Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 12 April 2020 doi:10.20944/preprints202004.0203.v1 Governments are evaluating the use of non-medical masks in the community amidst conﬂicting guidelines from health orga- nizations. This review synthesizes available evidence to pro- vide clarity, and advances the use of the ’precautionary princi- ple’ as a key consideration in developing policy around use of non-medical masks in public. Jeremy Howard prepared the initial literature list; Reshama Shaikh prepared the initial literature summaries; Frederik Questier did additional literature searches and summaries; Zhiyuan Li, Vi- olet Tang, Lei-Han Tang, and Danny Hernandez did impact modeling; Zeynep Tufekci provided sociological research and analysis; Helene-Mari van der Westhuizen and Arne von Delft provided analysis of additional impacts; Christina Bax provided review and feedback; All authors contributed to the writing. Anne W. Rimoin is an editor of the British Medical Journal. Larry F. Chu is a member of the editorial advisory board of the British Medical Journal. 1To whom correspondence should be addressed. E-mail: jphoward@usfca.edu 1–8 Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 12 April 2020 doi:10.20944/preprints202004.0203.v1 © 2020 by the author(s). Distributed under a Creative Commons CC BY license. This manuscript was compiled on April 12, 2020 Epidemiology, UCLA Fielding School of Public Health, 650 Charles E Young Drive, Los Angeles, CA 90095 NY 10031; r Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium; s University of Pennsylvania, 3400 Civic Center Blvd, Philadelphia, PA 19104; t Department of University of Cape Town, Anzio Road, Observatory, 7925, South Africa; p OpenAI, 3180 18th St, San Francisco, CA 94110; q Data Umbrella, 345 West 145th St, New York, Anesthesia Informatics and Media (AIM) Lab, Stanford University, 300 Pasteur Drive, Grant S268C, Stanford, CA 94305; o School of Public Health and Family Medicine, Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, China; m University of North Carolina at Chapel Hill; n School of Medicine for Quantitative Biology, Peking University, Haidian, Beijing 100871, China; l Department of Information Systems, Business Statistics and Operations Management, Hong University, Kowloon Tong, Hong Kong SAR, China; j Complex Systems Division, Beijing Computational Science Research Center, Haidian, Beijing 100193, China; k Center hDepartment of Biostatistics, UCLA Fielding School of Public Health, 650 Charles E Young Drive, Los Angeles, CA 90095; iDepartment of Physics, Hong Kong Baptist Czech Republic; f Department of Primary Health Care Sciences, Woodstock Road, University of Oxford, OX2 6GG, United Kingdom; g TB Proof, Cape Town, South Africa; Technology, 77 Massachusetts Ave, Cambridge, MA 02139; e Institute of Chemical Process Fundamentals, Czech Academy of Sciences, Rozvojová 135, CZ-165 02 Praha 6, University of San Francisco, 101 Howard St, San Francisco, CA 94105, US; d Department of Electrical Engineering & Computer Science, Massachusetts Institute of afast.ai, 101 Howard St, San Francisco, CA 94105, US; bWarren Alpert School of Medicine, Brown University, 222 Richmond St, Providence, RI 02903; cData Institute, Shaikhq , Frederik Questierr , Danny Hernandezp , Larry F. Chun , Christina M. Ramirezh , and Anne W. Rimoint von Delfto,g , Amy Pricen , Lex Fridmand , Lei-Han Tangi,j , Viola Tangl , Gregory L. Watsonh , Christina E. Baxs , Reshama Jeremy Howarda,c,1 , Austin Huangb , Zhiyuan Lik , Zeynep Tufekcim , Vladimir Zdimale , Helene-Mari van der Westhuizenf,g ,Arne Review Face Masks Against COVID-19: An Evidence