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Updated: December 3, 2020

Is there evidence regarding a correlation between COVID-19 infection rates and mask use?

Summary

The following is a short summary of the best available evidence from trusted sources that have been rated as providing high quality information on the correlation between COVID-19 infection rates and mask use. One rapid review, two rapid review and meta-analyses, one rapid response report, one rapid evidence check, one scientific brief, one single study, and three guidance documents were used in the creation of this REAL Summary. For additional information about each of the sources, see the Table below. For additional information about each of the sources, see the Table below.

The authors of Face masks and coverings for the general public, Facemask use in community settings to prevent respiratory infection transmission: a rapid review and meta-analysis, and Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis stated that medical masks are effective in reducing the transmission of COVID-19 when they are manufactured using optimal materials, are hybrid and multi-layered, and are correctly fitted to the wearer [1,2,3,5]. The Centers for Disease Control and Prevention (CDC) reports in its Scientific Brief: Community Use of Cloth Masks to Control the Spread of SARS-CoV-2, that materials such as polypropylene are more effective at filtering out droplets and particles, while materials like silk repel moisture and maintain breathability [6]. In addition to medical mask use, two meta-analyses recommend that further preventative measures including physical distancing and intensive hand hygiene are required in conjunction with community mask use [2,3]. In healthcare settings, it is recommended that N95 masks and respirators are used [3]. Medical masks should also be reserved for healthcare workers, and individuals with symptoms in the community [4]. 

In terms of cloth masks, one meta-analysis indicated that their use has no direct evidence in preventing COVID-19 transmission [2]. However, the CDC indicated that cloth masks provide some protection and those with a higher thread count and multiple layers of fabric are more effective than those with lower thread counts and only a single layer [6]. In addition, the CDC recommends that to reduce the risk of transmission, individuals wearing cloth masks should opt for non-valved options [6]. The Public Health Agency of Canada’s Non-medical masks and face coverings: About and the World Health Organization’s (WHO) updated guidance on the use of masks  recommends that a mask or face covering should consist of three layers with the following: a) two layers of tightly women material fabric; and b) a filter-like middle layer made out of fabric including polypropylene [8,9]. 

The authors of the Association of country-wide coronavirus mortality with demographics, testing, lockdowns, and public wearing of masks, single study analyzed 196 countries, and found that as the duration of mask-wearing by the public increased, the per-capita mortality decreased [7]. In addition, countries with cultural norms or governmental policies that support mask wearing, per-capita COVID mortality increased an average of 15.8% each week, while increasing by 62.1% each week in countries not supporting mask wearing [7]. 

Overall, the evidence between mask use and the prevention of COVID-19 transmission is relatively weak [1,2,4,5]. While randomized trails are lacking, and difficult to conduct in these context, many observational and case-control studies suggest that masks are protective [4], and guidance strongly proposes a precautionary approach. The Royal Society (UK), Alberta Health Services, The New South Wales Government and Public Health Ontario have all indicated that masks may provide a source of protection in community settings [1,4,5,10].

Evidence

What‘s Trending on Social Media and Media

On November 20, 2020, two professors at Simon Fraser University found that physical distancing is effective at reducing the spread of COVID-19, while masks are more situation-dependent. They note that masks may be less effective in high transmission settings (parties, choirs, restaurant kitchens, bars and nightclubs) because even if masks minimize transmission rates by half, that may not have much impact on the transmission probability. Find the article here.

On November 13, 2020, CBC’s Marketplace tested over 20 different masks to see the protection they offer. They suggest that people should look for a 3-layer mask, specifically cotton with inner layer melt-blown non-woven polypropylene or blue surgical-type mask, which they say perform well to filter particles. People should avoid the issue of masks with exhalation valves as they can disperse virus particles to others. Find more information about various mask materials here.

Organizational Scan

Johns Hopkins Medicine released answers to commonly asked questions about non-medical face masks and infection prevention. They state that face masks help prevent the transmission of SARS-CoV-2 virus, as a mask will help contain respiratory droplets from people who do not know they have the virus. Neck gaiters and bandanas are not as efficient as a double-layer washable covering — the neck gaiter is too thin to provide adequate protection, and a bandana is open at the bottom. Find more FAQs here [21].

Public Health Ontario states that public mask-wearing is likely beneficial as source control when worn by persons shedding infectious SARS-CoV-2 virus. Masking to protect the wearer is unlikely to be effective in non-healthcare settings. Also, mandatory public mask policies have been associated with a decrease in new COVID-19 cases compared to regions without such policies. This source summarizes statistical data (relative risk, odds ratio, frequency) from single studies on COVID-19 and non-COVID-19 respiratory infections [22].

Review of Evidence

Resource Type/Source of Evidence Last Updated
Face masks and coverings for the general public
— The Royal Society (UK) 		Rapid Review

·      Masks are effective at reducing transmission when masks are created using optimal materials (e.g., high grade cotton), are hybrid and multi-layered (e.g., using silk and cotton), and are fitted correctly for the wearer.

·     Mask use can provide source protection and protection for the wearer, (evidence is weak, and the effect is likely to be small). 

Last Updated: June 25, 2020
Facemask use in community settings to prevent respiratory infection transmission: a rapid review and meta-analysis
— Chaabna et al. 		Rapid Review & Meta-Analysis

·     Mask use is effective in preventing COVID-19 transmission when facemasks are of medical grade, are worn prior to the development of symptoms, and are used in conjunction with other preventative measures such as intensive hand hygiene. 

·     There is no direct evidence of cloth masks preventing COVID-19 infection. 

Last Updated: September 25, 2020
Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis
— Chu et al. 		Rapid Review & Meta-Analysis

·     Mask use can reduce the risk of COVID-19 infection, with stronger evidence for N95 masks and similar respirators compared to surgical masks or 12-16-layer cotton masks.

·     The authors suggest that effectiveness of mask use depends on contextual factors but recommends N95 and respirator use for health-care settings, and surgical and cotton masks for community settings.

·     Risk of infection can also be reduced with physical distancing of at least 1 meter (2 meters more effective) and use of eye protection.

Last Updated: May 31, 2020
What is the effectiveness of wearing medical masks, including home-made masks, to reduce the spread of COVID-19 in the community?
— Alberta Health Services 		Rapid Response Report

·     Discusses research gaps regarding mask efficacy and outlines many scientific reports regarding the use of medical and non-medical masks in a community setting. 

·     While it was agreed that there was a lack of randomized trials indicating that medical masks reduced transmission of acute respiratory infections, many observational and case-control studies suggested masks are protective. 

·     There was an agreement that the use of masks in the community is likely to be useful in reducing transmission of respiratory illnesses. 

·     Medical masks should be reserved for healthcare workers, and individuals with symptoms in the community. 

Last Updated: June 18, 2020
Face masks and COVID-19 transmission in the community
— The New South Whales Government 		Rapid Evidence Check

·     There is conflicting evidence on the association between mask use and COVID-19 transmission. and that filtering efficacy of masks varies depending on the materials used in the mask. 

·     There is no direct evidence of mask use being an added benefit when other preventative measures such as hand hygiene and social distancing are in place. 

·     Mask use may play a role in reducing community transmission in settings where social distancing is not feasible. 

Last Updated: July 19, 2020
Scientific Brief: Community Use of Cloth Masks to Control the Spread of SARS-CoV-2
— CDC: Centers for Disease Control and Prevention 		Scientific Brief

·     Approximately 50% of transmissions of the COVID-19 virus are by individuals who are asymptomatic or pre-symptomatic. 

·     To reduce the risk of transmission, it is recommended to wear non-valved cloth masks.

·     Materials such as polypropylene are more effective at filtering out fine droplets and particles, while materials like silk repel moisture and maintain breathability. 

·     Cloth masks with a higher thread count and multiple layers of fabric are more effective than masks made of fabric with lower thread counts and a single layer of fabric.  

Last Updated: November 19, 2020
Association of country-wide coronavirus mortality with demographics, testing, lockdowns, and public wearing of masks
— Leffler et al. 		Single Study

·     Findings from an analysis across 196 countries found an association whereas the duration of mask-wearing by the public increased, the per-capita mortality decreased.

·     In countries with cultural norms or governmental policies that support mask wearing, per-capita COVID mortality increased an average of 15.8% each week, while increasing by 62.1% each week in other countries. 

Last Updated: August 3, 2020
Non-medical masks and face coverings: About
— Public Health Agency of Canada 		National Guidance

A mask or face covering should:

·     be at least three layers;

·     two layers should be tightly woven material fabric;

·     the third (middle) layer should be a filter-type; fabric, such as non-woven polypropylene fabric;

·     completely and comfortably cover the nose, mouth and chin without gaping;

·     allow for easy breathing;

·     fit securely to the head with ties or ear loops;

·     not require frequent adjustments;

·     be changed if damp or dirty; and

·     maintain its shape after washing and drying.

Last Updated: November 2, 2020
WHO updated guidance on the use of masks
— World Health Organization 		International Guidance

Masks should not be:

·     one layer

Masks should:

·     be easily breathable;

·     be made with fabrics which can be washed in high temperatures regularly;

·     have an inner layer of absorbent material, such as cotton;

·     have a middle layer of non-woven material, such as polypropylene; and

·     have an outer layer of non-absorbent material, such as polyester or polyester blend.

Last Updated: June 11, 2020
Wearing Masks in Public and COVID-19 – What We Know So Far
— Public Health Ontario 		Provincial Guidance

·     Mandatory public mask policies have been associated with a decrease in new COVID-19 cases compared to regions without such protocols. 

·     Public mask wearing is likely beneficial as source control when worn by people who are shedding the infectious SARS-CoV-2 virus.

Last Updated: September 13, 2020
Coronavirus Face Masks & Protection FAQs
— Johns Hopkins Medicine 		Organizational Scan Last Updated: October 15, 2020
Wearing Masks in Public and COVID-19
— Public Health Ontario 		Organizational Scan Last Updated: September 13, 2020
Disclaimer: The summaries provided are distillations of reviews that have synthesized many individual studies. As such, summarized information may not always be applicable to every context. Each piece of evidence is hyperlinked to the original source.