memo
COVID-19-EPIDEMIC :Should individuals in thecommunity without
respiratory symptoms wear
facemasks to reduce thespread of COVID-19?
– a rapid review

TitleShould individuals in the community without respiratory symptoms wear
facemasks to reduce the spread of COVID-19?

Institution

Folkehelseinstituttet / Norwegian Institute of Public HealthResponsible

Camilla Stoltenberg, Director-General

Authors
ISBN

Iversen BG, Vestrheim DF, Flottorp S, Denison E, Oxman AD, NorwegianInstitute of Public Health978-82-8406-106-1

Memo

June – 2020

Publication type

Rapid review

Number of pages

43

Commissioned by

Folkehelseinstituttet / Norwegian Institute of Public Health

CitationIversen BG, Vestrheim DF, Flottorp S, Denison E, Oxman AD. COVID-19:
Should individuals in the community without respiratory symptoms wear
facemasks to reduce the spread of COVID-19? [Covid-19: Bør personer isamfunnet bruke ansiktsmasker for å redusere spredningen av covid-19?
Hurtigoversikt 2020] Oslo: Norwegian Institute of Public Health, 2020.

Key messages

Health authorities have given conflicting recommendations regarding the use of facemasks
by asymptomatic individuals in the community to reduce the spread of COVID-19. For example, the World Health Organization (WHO) states that “at present, there is no direct evidence (from studies on COVID-19 and in healthy people in the community) on the effectiveness of universal masking of healthy people in the community to prevent infection with respiratory viruses, including COVID-19”. Yet, “WHO has updated its guidance to advise that toprevent COVID-19 transmission effectively in areas of community transmission, governments should encourage the general public to wear masks in specific situations and settings
as part of a comprehensive approach to suppress SARS-CoV-2 transmission”. This includes
settings where individuals are unable to keep a physical distance of at least 1 meter. WHO
is also strongly encouraging countries to conduct research on this critical topic.
An Evidence to Decision (EtD) framework was used to guide the process from reviewing theevidence to a recommendation. An evidence base was made by a structured literature review using the L·OVE COVID-19 database and a living COVID-19 evidence map. Relevant ongoing reviews and studies were searched for in PROSPERO, the list of COVID-19 trials in theInternational Clinical Trials Registry Platform (ICTRP) (updated 12 May 2020) and ClinicalTrials.gov COVID-19 list. Additional articles were identified by checking the references in retrieved articles and personal contacts.
There is evidence of a protective effect of medical facemasks against respiratory infections
in community settings. However, study results vary greatly. Randomised trials from community settings indicate a small protective effect. Laboratory studies indicate a larger effectwhen facemasks are used by asymptomatic but contagious individuals to prevent the
spread of virus to others, compared to use by uninfected individuals to prevent themselvesfrom becoming infected. Because incorrect use of medical facemasks limits their effectiveness, countrywide training programmes adapted to a variety of audiences would be needed
to ensure the effectiveness of medical facemasks for reducing the spread of COVID-19. It is
not known whether the use of medical facemasks would be widely accepted by the healthy
population in Norway, or the extent to which correct use could be achieved.
Non-medical facemasks include a variety of products. There is no reliable evidence of theeffectiveness of non-medical facemasks in community settings. There is likely to be substantial variation in effectiveness between products. However, there is only limited evidence from laboratory studies of potential differences in effectiveness when different products are used in the community.
Given the low prevalence of COVID-19 currently, even if facemasks are assumed to be effective, the difference in infection rates between using facemasks and not using facemasks
would be small. Assuming that 20% of people infectious with SARS-CoV-2 do not havesymptoms, and assuming a risk reduction of 40% for wearing facemask, 200 000 people
would need to wear facemasks to prevent one new infection per week in the current epidemiological situation.
2

The undesirable effects of facemasks include the risks of incorrect use, a false sense of security (leading to relaxation of other interventions), and contamination of masks. In addition, some people experience problems breathing, discomfort, and problems with communication. The proportion of people who experience these undesirable effects is uncertain.
However, with a low prevalence of COVID-19, the number of people who experience undesirable effects is likely to be much larger than the number of infections prevented.
An expert panel discussed and assessed the evidence using an explicit set of criteria. The
panel did not take into consideration the shortage of medical facemasks. The assessments
for each criterion were judged both individually and in a consensus process, and the overall
recommendation and report were reviewed by the panel.

Conclusion
In the current epidemiological situation in Norway, wearing facemasks to reduce the spreadof COVID-19 is not recommended for individuals in the community without respiratory
symptoms who are not in near contact with people who are known to be infected. If theepidemiological situation worsens substantially in a geographical area, the use of facemasks
as a precautionary measure should be reconsidered. Measures to reduce risks during necessary public transport and during mass events, including wearing facemasks, should be explored further.
If use of facemasks by individuals without respiratory symptoms in the community is recommended in specific circumstances, such as public transport or mass events, medical
masks or quality controlled non-medical masks with a documented filtration effect should
be used. National priorities for the use of personal protective equipment may apply, given
existing shortages. If any such recommendation is made, the community should be given
training to ensure correct use and the risks should be explained, especially the risks of a
false sense of security and contamination of masks. The training should be tailored to theneeds of different groups, including people with different levels of fluency in Norwegianand different socio-economic circumstances.

3

Hovedbudskap

Helsemyndigheter har gitt ulike anbefalinger om hvordan bruk av munnbind og ansiktsmasker blant asymptomatiske personer kan bidra til å redusere spredningen av covid-19-infeksjon i samfunnet. For eksempel uttaler Verdens helseorganisasjon (WHO) at “foreløpig finnes det ikke direkte dokumentasjon (fra studier på covid-19 og hos friske personer i samfunnet) om effekten av generell bruk av ansiktsmasker blant friske personer i samfunnet forå forhindre infeksjon med luftveisvirus, inkludert covid-19”. Likevel, “WHO har oppdatert
sin veileder og anbefaler at, for å effektivt forebygge smitte av covid-19 i områder med
smittespredning i samfunnet, bør regjeringer oppfordre allmennheten til å bruke masker
under gitte forutsetninger og situasjoner som ledd i en helhetlig tilnærming for å redusere
smittespredning”. Dette inkluderer situasjoner der personer ikke kan holde en fysisk avstand på minst 1 meter. WHO oppfordrer sterkt til å forske mer på dette viktige temaet.
Vi benyttet et Evidence to Decision (EtD) rammeverk til å gjennomgå kunnskapen og utarbeide en anbefaling. Kunnskapsbasen var basert på en strukturert gjennomgang av L·OVE
COVID-19-databasen og et levende kart over covid-19 forskning. Vi søkte etter pågående
oversikter og studier i PROSPERO, listen over covid-19-studier i International Clinical Trials
Registry Platform (ICTRP) (oppdatert 12. mai 2020) og ClinicalTrials.gov covid-19-listen. Vi
fant ytterligere noen artikler ved å sjekke referanselistene i identifiserte artikler og gjennom personlige kontakter.
Det finnes dokumentasjon for at medisinske munnbind kan ha beskyttende effekt mot
spredning av luftveisinfeksjoner i samfunnet, men resultatene varierer. Randomiserte studier gjennomført utenfor helseinstitusjoner tyder på at munnbind har en liten beskyttendeeffekt. Laboratoriestudier indikerer at effekten er større når munnbind brukes for å forhindre spredning fra asymptomatiske, smittsomme individer, sammenlignet med når ikkesmittede personer bruker munnbind for å forhindre at de selv blir smittet. Uriktig bruk av
medisinske munnbind reduserer effekten, og det vil derfor være behov for opplæring tilpasset ulike målgrupper for å sikre effektiv bruk av medisinske munnbind. Vi vet ikke om den
friske befolkningen i Norge vil akseptere å bruke medisinske munnbind, og vi vet ikke i hvilken grad vi kan oppnå riktig bruk av munnbind.
Ikke-medisinske ansiktsmasker omfatter mange ulike produkter. Det er ingen pålitelig dokumentasjon for effekten av ikke-medisinske ansiktsmasker brukt i samfunnet. Det vil sannsynligvis være betydelig variasjon i effekt mellom de ulike produktene. Vi har begrenset dokumentasjon fra laboratorieundersøkelser om mulige forskjeller i effekt når ulike produkter
brukes av personer i samfunnet, utenfor helsetjenesten.
Gitt den lave utbredelsen av covid-19 for øyeblikket, og selv om ansiktsmasker antas å væreeffektive, vil forskjellen i infeksjonsraten mellom å bruke eller ikke å bruke ansiktsmaskervære liten. Hvis vi antar at 20% av smittsomme personer med SARS-CoV-2 ikke har symptomer, og videre antar en risiko reduksjon på 40% ved å bruke ansiktsmaske, så må 200 000
personer bruke ansiktsmaske per uke for å forebygge ett nytt tilfelle i den nåværende epidemiologiske situasjonen.
4

Ulemper ved bruk av ansiktsmasker omfatter risiko for feil bruk, falsk trygghetsfølelse (somkan føre til lemping av andre tiltak) og tilskitning av maskene. Noen opplever også pustebesvær, andre ubehag og kommunikasjonsvansker. Hvor mange mennesker som oppleverdisse ulempene er usikkert. Med en lav forekomst av covid-19, vil antagelig personer som
opplever ulemper sannsynligvis være mye større enn antall infeksjoner som forebygges.
Et ekspertpanel diskuterte og vurderte dokumentasjonen ved bruk av et forhåndsdefinert
sett med kriterier. Panelet tok ikke hensyn til en mulig mangel på medisinske munnbind.
Evalueringene for hvert kriterium ble bedømt både individuelt og i en konsensusprosess, og
den samlede anbefalingen og rapporten ble gjennomgått av panelet.

Konklusjon
I den nåværende epidemiologiske situasjonen i Norge anbefaler vi ikke å bruke ansiktsmasker for å redusere spredningen av covid-19 for personer i samfunnet uten luftveissymptomer og som ikke er i nærkontakt med personer med kjent smitte. Hvis den epidemiologiske
situasjonen forverres vesentlig i et geografisk område, bør bruken av ansiktsmasker som etforebyggende tiltak vurderes på nytt. Tiltak for å redusere risikoen ved bruk av offentlig
transport og under arrangementer med mange til stede, inkludert bruken av ansiktsmasker,
bør utredes nærmere.
Hvis man anbefaler bruk av ansiktsmasker hos personer uten luftveissymptomer i samfunnet i gitte situasjoner, for eksempel ved offentlig transport eller større arrangementer, bør
medisinske munnbind eller kvalitetskontrollerte ikke-medisinske ansiktsmasker med dokumentert filtreringseffekt brukes. Ved mangel på personlig beskyttelsesutstyr kan man iverksette prioriteringer av grupper for bruk. En slik anbefaling bør følges opp med opplæringstiltak for å sikre korrekt bruk, og risiko knyttet til falsk trygghetsfølelse og tilskitning av masker bør formidles. Opplæringen bør være tilpasset behovene til forskjellige grupper, inkludert mennesker med ulik norskforståelse og sosioøkonomisk bakgrunn.

5

Contents

KEY MESSAGES

2

HOVEDBUDSKAP

4

CONTENTS

6

PROBLEM STATEMENT

7METHOD

8

Process overview

8

Search strategy

8

Selection criteria

9

Data collection

10

Panel discussion and judgement

11

RESULTS

12

Direct evidence of the effects of facemasks on preventing COVID-19 infections

13

Evidence of the effects of facemasks on preventing other respiratory infections

13

Evidence from laboratory studies

14

Additional considerations

14

Panel discussion and judgment

15

DISCUSSION AND CONCLUSION

20

Discussion

20

Conclusion

21

Limitations

21

LIST OF REFERENCES

23

SUPPLEMENTARY TABLES AND FIGURES26

APPENDIX. UPDATED SEARCH 9 JUNE 2020

40

6

Problem statement

Health authorities have given conflicting recommendations regarding the use of facemasks
by asymptomatic individuals in the community to reduce the spread of COVID-19. For example, The World Health Organization (WHO) recommends that "In settings where medical
masks are in short supply, medical masks should be reserved for health workers and at-risk
individuals when indicated.” 1. With respect to non-medical facemasks, WHO advises: "Theuse of facemasks made of other materials (e.g., cotton fabric), also known as non-medical
facemasks, in the community setting has not been well evaluated." "WHO is also strongly
encouraging countries that issue recommendations for the use of facemasks in healthy people in the community to conduct research on this critical topic." 2Using an Evidence to Decision (EtD) framework, a panel at the Norwegian Institute of Public
Health (NIPH) developed a recommendation addressing the question “Should individuals in
the community without respiratory symptoms wear facemasks to reduce the spread of
COVID-19?”
Screening of research evidence and monitoring of the situation in Norway is ongoing. The
EtD framework will be updated and the recommendations reviewed (and revised, if indicated) when new research becomes available, or if the situation in Norway changes.

7

Method

Process overview
We used an Evidence to Decision (EtD) framework to guide the process from reviewing theevidence to a recommendation. EtD frameworks are used to help make recommendations
or decisions by moving from evidence to decisions in a structured way (https://ietd.epistemonikos.org/#/about/introduction)3,4. The process ensures that the pros and cons and important criteria for decisions are considered, and makes the decision process transparent.
EtD frameworks also make it possible for people to understand the basis for recommendations.
The process included gathering and reviewing evidence, discussion, and assessment by anexpert panel using an explicit set of criteria. The assessments provided the basis for a conclusion and recommendation.

Search strategy
This EtD framework and a second framework (regarding the use of facemasks by asymptomatic healthcare personnel in nursing homes) were developed rapidly, due to the urgencyof the questions. Final decisions about the content of the EtD framework were made by thepanel responsible for the recommendations. Screening of research evidence and monitoring of the situation in Norway is ongoing.
All articles coded as “Treatment or prevention, Coronavirus infection, and Masks” in the
L·OVE COVID-19 database5 were screened. This database includes systematic reviews andstudies, published or ongoing, of any design identified using multiple search strategies(https://app.iloveevidence.com/covid-19).6 At the time of the most recent search (13 May
2020), over 100,000 records have been processed for inclusion in this database.
All articles coded as “Infection prevention and control, Infection prevention and control
policies, Physical barriers, Use of masks” in the NIPH COVID-19 evidence map werescreened.7 The evidence map includes systematic reviews and studies identified by screening literature searches that are conducted daily or every other day in PubMed and supplemented by regular updates with material retrieved by searches performed by organizations
such as WHO, CDC and others.8 At the time of the most recent search (13 May 2020),
15,404 references had been screened and the map contained 1,779 publications.
PROSPERO9 was searched (13 May 2020) for systematic reviews in progress using the
COVID-19 filter and “masks”. The list of COVID-19 trials in the International Clinical Trials
Registry Platform (ICTRP) (updated 12 May 2020)10 and ClinicalTrials.gov COVID-19 list ofregistered studies (13 May 2020)11 were searched for studies in progress using “masks”.
8Additional articles were identified by checking the references in retrieved articles andthrough personal contacts.

Selection criteria
Below we describe how we included relevant research evidence for each criterion in the
EtD framework. References that described important considerations that may not havebeen addressed by available research evidence were included under “Additional considerations”.

Priority of the problem
Any research, including modelling studies, of COVID-19 infection rates in Norway, outbreaks in nursing homes in Norway, or the availability of cloth, medical or N95 facemasks.
Information about infection rates from NIPH weekly reports is included under “Additional
considerations”.

Effects of using facemasks or advice to use facemasksa) Direct evidence
Any randomised or non-randomised study that estimated the effect on COVID-19 infections
or any other important outcome for any kind of facemask used by asymptomatic individuals
in the community or by asymptomatic people working in long-term care facilities. The inclusion criteria were:






P: People potentially exposed to COVID-19
I: Use of or advice to use any kind of facemask
C: non-use of facemasks, no advice to use facemasks, or use of a different kind of
facemask
O: any important outcome
Study design: any quantitative, comparative study designb) Systematic reviews of randomised and non-randomised studies of the effects of
facemasks to reduce the spread of respiratory infections
Any systematic review that directly addressed the effects of using facemasks or advice touse facemasks for primary prevention (when no cases have yet been identified) of respiratory infections. The following criteria were used to select the primary systematic review
summarised in the EtD: comprehensiveness, inclusion of both randomised and non-randomised studies, sensible grouping of studies in meta-analyses and forest plots, assessments of the risk of bias, and a Summary of Findings with assessments of the certainty ofthe evidence using GRADE12 or a similar explicit approach. Other systematic reviews that
did not meet the inclusion criteria were used to supplement the findings of the primary systematic review.

c) Systematic reviews comparing different types of facemasks
Any systematic review of randomised or non-randomised studies comparing the effectiveness of different types of facemasks for preventing respiratory infections, randomised trials
9not included in a systematic review, and any randomised or non-randomised study comparing the use of different types of facemasks for COVID-19.

d) Laboratory studies
Systematic reviews of laboratory studies of the filtering effects of different types of facemasks for respiratory infections, any laboratory study of the filtering effects of different
types of masks for COVID-19 not included in a systematic review, and laboratory studies ofdifferent types of masks for other respiratory infections that were considered relevant for
COVID-19.

ValuesAny research that measured how people value the potential benefits and harms of facemasks or advice about facemasks.

Resources required
Any research that estimated the potential costs and savings of the use of any type of facemask by asymptomatic individuals in the community or by asymptomatic people working in
long-term care facilities.

Cost-effectivenessAny cost-effectiveness analysis that used a transparent model, a plausible range of values,
and sensitivity analyses that address the uncertainties in the estimates and assumptions
that were used in the model.

EquityAny research that addressed impacts or potential impacts of facemask use on equity.

Acceptability
Any research that investigated the acceptability of facemask usage or recommendations forusing facemasks.

Feasibility
Any research that investigated the feasibility of implementing recommendations to use
facemasks.

Data collection
Judgements about which articles to include and what information to include in the draft
EtD frameworks were made by AO, who applied criteria described above, summarised key
findings from included research, and identified additional considerations noted in the literature that was reviewed.
Assessments of the risk of bias and the certainty of the evidence were based on the judgements of authors of included systematic reviews, whenever possible. The risk of bias of the
primary systematic review used to inform judgements about the effects of facemasks wasassessed by ED using ROBIS (Table S1).13

10

Panel discussion and judgement
The final content of the EtD framework was determined by the expert panel. The panel consisted of six co-workers with the Division of infectious disease control at NIPH (Senior Advisor Torunn Alberg, Senior Medical Officer Tone Bruun, Senior Advisor Mette Fagernes, Senior Medical Officer Siri Feruglio, Specialty Director Frode Forland, and Senior Medical Officer Bjørn Iversen). The evidence and additional considerations were presented to thepanel, followed by a discussion and judgments for each assessment criteria. A summary ofthe discussion was entered in the iEtD framework. The panel agreed on a consensus for assessment of all the criteria for each of the questions. The group also made individual judgements. This informed the consensus.
The assessment criteria that were judged by the panel were those included in the framework for health system and public health recommendations: Problem Effects;
o Desirable effects
o Undesirable effects
o Certainty of the evidenceo Valueso Balance of effects
 Resources, includingo Resources requiredo Certainty of evidence of required resourceso Cost-effectiveness Equity Acceptability
 Feasibility

A summary of the panel discussions is included under Results. The panel reviewed the report before publication.

11

Results

As of 13 May 2020, 24,748 articles about COVID-19 were screened for the L·OVE COVID-19
database and 4043 were selected as relevant for decision-making, including 391 systematic
reviews, 3652 primary studies (including 551 randomised trials). 3163 articles did not report
data yet (e.g. ongoing trials). 138 articles were identified as relevant for masks for coronavirus infection, including 19 systematic reviews and 118 primary studies (including nine randomised trials).
The NIPH COVID-19 evidence map included 24 references, including nine systematic reviews, four non-systematic reviews, ten studies (including models), and one article that reported a study and a non-systematic review.
PROSPERO included 885 records using the COVID-19 filter of which 88 included the word
“masks”. Thirty-nine of those were registered in 2020 and were screened. Only two records in the list of COVID-19 trials in the International Clinical Trials Registry Platform (ICTRP)
included the word “masks”. Sixty-two records in the ClinicalTrials.gov COVID-19 list of registered studies included the word “masks”.
Judgements about the eligibility of the articles that were screened for the draft EtD frameworks are summarised in a flow diagram (Supplement Figure 1). A total of 264 records werescreened after duplicates were removed. Forty-nine articles were included, of which 16
were records for systematic reviews in progress and two were records for randomised trials
in progress. Two models were found that could inform judgements about the priority of the
problem.14, 15
One systematic review was used as the primary systematic review for effects for the EtD
framework.16 This was the only review that included a GRADE Summary of Findings table
and it appeared to be the most comprehensive and balanced of the systematic reviews thatwere found. The review is a preprint, not yet peer reviewed preprint, posted April 6, 2020.
Based on the ROBIS assessment, the systematic review was judged to have a low risk of bias
(Supplement Table 1).
Seven other systematic reviews provided some supplementary information (Supplement
Table 2). One randomised trial, 17 three non-randomised studies (Supplement Table 3), 11
laboratory studies (Supplement Table 4), and two models of the effects of masks18, 19 werealso included. Sixteen protocols for systematic reviews related to the effects of facemasks
and two protocols for randomised trials were found (Supplement Table 5).
One protocol for a systematic review of the direct costs and socioeconomic costs relating to
non-pharmaceutical interventions against infectious disease outbreaks was found.20 One
systematic review of economic evaluations was included.21 Two qualitative evidence syntheses22, 23 and one study24 of barriers and facilitators were found. No research addressing
12how people value the potential benefits and harms of using facemasks or impacts on equity
were found.
Twenty-two full-text articles that were not included (some of which are referenced as background information or under additional considerations) are listed in Supplement Table 6.

Direct evidence of the effects of facemasks on preventing COVID-19 infections
There is limited direct evidence of the effect of using facemasks in community settings on
COVID-19 infection rates. This evidence comes from ecological studies, summarised in Supplement Table S3. These studies have a high risk of bias.
One randomised trial of the use of medical facemasks by people working outside of theirhome to prevent COVID-19 infections is ongoing in Denmark25. That trial is evaluating theeffect on COVID-19 infections in people wearing facemasks, not on COVID-19 infections inpeople exposed to asymptomatic but infected individuals. No other trials of the use of medical or non-medical facemasks outside of healthcare settings are currently registered in
the International Clinical Trials Registry Platform (ICTRP) or ClinicalTrials.gov.

Evidence of the effects of facemasks on preventing other respiratory infections
A systematic review of the effects of facemasks to prevent other respiratory infections
found three randomised trials that provide evidence of low certainty that wearing medical
facemasks in community settings may reduce the odds of primary infection with influenzalike illness by around 6% 16. (Supplement Figures 2, 3 and 4) This estimate is based on two
studies in university residencies and one in Hajj pilgrims. It is very uncertain whether theeffect estimate is applicable to the use of either medical or non-medical facemasks byasymptomatic individuals in the community to prevent COVID-19 transmission.
Other randomised trials of facemasks are less applicable to the use of facemasks in thecommunity for primary prevention of COVID-19, and effect estimates from non-randomised
studies vary widely 16. Brainard and colleagues found one cohort study (using data from arandomised trial of supplements to reduce or prevent common colds) and one case control
study that estimated the association between wearing facemasks and primary preventionof respiratory infections in the general community. The cohort study, which included
healthy adult volunteers in Japan, included "habit of wearing facemasks" (undefined) as anindependent variable. It did not find an association between wearing facemasks and common colds (OR 0.85; 95% CI 0.37 to 1.94) in the intervention group and OR 0.94 (95% CI
0.43 to 2.03) in the control group. The case-control study included probable and suspected
SARS cases and controls in Beijing in 2003 and controls matched by sex and age group. In a
multivariate analysis, “always wearing a facemask when going out” was associated with areduction in the risk of clinically diagnosed SARS (OR 0.3; 95% CI 0.1 to 0.6). “Sometimes
wearing a facemask when going out” was also associated with a reduction in risk (OR 0.4;
95% CI 0.2 to 0.9). Both studies have a high risk of bias.
There is limited evidence from randomised or non-randomised studies of the effects ofnon-medical facemasks on preventing respiratory infections 26. One cluster-randomised
trial of cloth facemasks compared with medical facemasks in hospital healthcare workers
found higher rates of influenza-like illness and laboratory-confirmed virus when cloth facemasks were used compared to medical facemasks or normal practice (which may or may
not have included wearing a facemask) 27.
13

Evidence from laboratory studies
Evidence from laboratory filtration studies suggests that non-medical facemasks may reduce the transmission of larger respiratory droplets. There is little evidence regarding transmission of small aerosolized particulates of the size potentially exhaled by asymptomatic orpresymptomatic individuals with COVID-19 28. Key findings of relevant laboratory studies
are summarised in Supplement Table S4. These studies provide some information about thepotential effectiveness of facemasks for preventing COVID-19 infections. They do not provide evidence of the actual effects of facemask use or policies to promote facemask use.

Additional considerations
Impact of the construction of non-medical facemasks
A study of how well different fabrics (woven, woven brushed, knitted, knitted brushed,knitted pile) and materials (cotton, polyester, polypropylene, silk) found wide variation in
filtration efficiency (ability to stop particles) 28. Fabrics with greater breathing resistance
had higher filtration efficiency. However, facemasks with greater breathing resistance are
more difficult for users to wear consistently, which could reduce their effectiveness. Fit offacemasks may also be important since particles can escape through creases and gaps between the mask and face.

Impact of reusing non-medical facemasks
Cloth facemasks may need to be washed or decontaminated between uses. Various decontaminated methods have been documented, for example, autoclave, isopropyl alcohol,
bleach, hydrogen per oxide, microwave, soap and water, ultraviolet radiation, and dry heat.
While, the material of cloth facemasks is unlikely to degrade with standard means of disinfection (e.g., chemicals, heat, and radiation), unlike other types of disposable facemasks or
respirators, there is little evidence about the effectiveness of these decontamination methods25.

Impact of correct use of facemasks
The effectiveness of facemasks depends on correct use. Even if a facemask has a high filtration efficiency and fits well, its effectiveness depends on how well individuals put it on andkeep it in place. Moisture saturation is inevitable with fabrics available in most homes.
Moreover, moisture can trap virus and become a potential contamination source for others, after a mask is removed28.

Potential adverse effects of using facemasks
Potential adverse effects of using facemasks include28:





14

self-contamination by touching and reusing contaminated facemasks
breathing difficulties
a false sense of security, leading to less adherence to physical distancing and handwashinga shortage of facemasks for healthcare workers

Panel discussion and judgment
When assessing the criteria in the EtD framework, the panel considered both the evidence
and additional data. The panel also discussed each of the criteria before reaching a consensus.
The consensus judgements following the panel discussions are summarised in tables 1 to 3.
Table 1. Panel consensus on Medical facemasks or advice to wear medical facemasks
Favours
medicalfacemasks

ProblemDesirable effects
Undesirable effects
Certainty of the evidence
ValuesBalance of effects
Resources required
Certainty of evidence of required
resources
Cost-effectiveness
EquityAcceptability
Feasibility

15

Probably
favours
medicalfacemasks

Neither favours
medicalfacemasksor other
options

Probably
does notfavourmedicalfacemasks

Does notfavourmedicalfacemasks















Table 2. Panel consensus on Non-medical facemasks or advice to wear non-medical facemasks
Favours
non-medical facemasks

Probably
favours
non-medical facemasks

ProblemDesirable effects
Undesirable effects
Certainty of the evidence
ValuesBalance of effects
Resources required
Certainty of evidence of required
resources
Cost-effectiveness
EquityAcceptability
Feasibility

Neither favours nonmedical
facemasksor other
options

Probably
does notfavournon-medical facemasks
Does notfavournon-medical facemasks














Table 3. Panel consensus on No facemasks or no advice to wear or not to wear facemasks
Favours
no facemasks

ProblemDesirable effects
Undesirable effects
Certainty of the evidence
ValuesBalance of effects
Resources required
Certainty of evidence of required
resources
Cost-effectiveness
EquityAcceptability
Feasibility
16

Probably
favours
no facemasks

Neither favours nofacemasksor other
options















Probably
does notfavour no
facemasks

Does notfavour no
facemasks

Problem - Is the problem a priority?
Preventing spread of COVID-19 from symptomatic or pre-symptomatic cases in the community is a high priority. It is likely that asymptomatic infections contribute to the spread of
the infection. In the present situation, the prevalence of COVID-19 in the general population is very low. Given that symptomatic cases comply with the recommendation to stay inisolation at home, or in health care, the probability of a random meeting between a pre- or
asymptomatic case and a susceptible person in the general population in Norway today isextremely low (1 in 50 000). 29
The panel discussed how a change in incidence could influence these judgements. An increase in the prevalence of contagious people without symptoms, either locally or nationally, should prompt a re-evaluation of the problem. The panel did not decide on a threshold.

Desirable effects - How substantial are the desirable anticipated effects?
There is evidence for a protective effect of medical facemasks in community settings. However, study results vary greatly. Randomised trials from community settings indicate a small
protective effect. Laboratory studies indicate a larger effect when facemasks are worn byasymptomatic but contagious individuals to prevent the spread of virus, than when they areworn by susceptible individuals to protect themselves from becoming infected. To ensure
correct use of facemasks, country-wide training programmes adapted to a variety of audiences would need to be implemented. It is not known whether the use of medical facemasks by the healthy population would be widely acceptable or the extent to which correct
use could be achieved.
Non-medical facemasks include a variety of products. There is no reliable evidence of theeffectiveness of non-medical facemasks in community settings. There is likely to be substantial variation in effectiveness between products. However, there is only limited evidence from laboratory studies of potential differences in effectiveness when different products are used in the community.
Given the low prevalence of COVID-19 currently, even if facemasks are assumed to be effective, the difference in infection rates between using facemasks and not using face-masks
would be small.

Undesirable effects - How substantial are the undesirable anticipated effects?
The undesirable effects of facemasks include the risks of incorrect use, a false sense of security (leading to relaxation of other interventions), and contamination of masks. In addition, some people experience problems breathing, discomfort, and problems with communication. The proportion of people who experience these undesirable effects is uncertain.
However, with a low prevalence of COVID-19, the number of people who experience undesirable effects is likely to be much larger than the number of infections prevented.

Certainty of the evidence - What is the overall certainty of the evidence of effects?
There is low-certainty evidence for a protective effect of medical facemasks used in a community setting from randomised trials and inconsistent evidence from non-randomised
studies. Evidence of the magnitude of undesirable effects is lacking.
Evidence of the desirable effects of non-medical facemasks is very uncertain. The range ofdifferent products, without standards for production, contributes to the uncertainty. The
undesirable effects of non-medical facemasks are also not well documented.
17

The effectiveness of facemasks for primary prevention compared to not using facemasks is
uncertain. At the same time, it is certain that facemasks have some undesirable effects
compared to not using facemasks, although the magnitude of the undesirable effects is uncertain.

Values – Is there important uncertainty about, or variability in, how much people
value the main outcomes?
The value (importance) of limiting the spread of COVID-19 in the population is likely to be
dependent on the prevalence and knowledge about the risk of severe disease. The panel
believes that the potential desirable and undesirable effects of using facemasks are likely to
be valued differently by the elderly and persons belonging to high-risk groups than byyounger people without risk factors.

Balance of effects – Does the balance between desirable and undesirable effects
favour the option or the comparison?
The available research evidence suggests a small desirable effect of individuals in the community without symptoms using medical facemasks to prevent the spread of virus. However, there are important undesirable effects. The number needed to mask to prevent one
infection is highly dependent on the incidence of COVID-19.

Given the current estimated infection rate of five cases per 100,000 people per week in
Norway 29, large numbers of people would need to wear facemask in order to prevent infections. Brainard et al. estimated a relative risk reduction of 6%, whereas Chu et al. gave
an unadjusted estimate for non-healthcare settings of 44%, and the adjusted estimate forusing surgical facemasks of 67%. Assuming that 20% of people infectious with SARS-CoV-2
do not have symptoms, the following number of people would need to wear a mask for aweek to prevent one person from becoming infected:
Risk reduction
6%
40 %
70 %

Weekly incidence per 100 000
51015
1 333 000
667 000
444 000
200 000
100 000
67 000114 000
57 00038 00020
333 000
50 00029 000The panel judged that with the current low incidence of COVID-19 in Norway, the balanceof effects does not favour using medical facemasks.
The desirable effects of non-medical facemasks are uncertain, while the potential undesirable effects are the same as for medical facemasks and may occur more frequently. With thecurrent low incidence of COVID-19 in Norway, the panel judged the balance of effects does
not favour using non-medical facemasks.
The panel judged that the balance of effects favours not using facemasks by individuals in
the community without symptoms to prevent the spread of virus.

Resources required – How large are the resource requirements (costs)?
The resources required are uncertain. However, the masks have a cost. A mask should not
be used over a long time. The 'number needed to mask' to prevent one case of COVID-19 ishighly dependent on the incidence and should be considered before making any recommendation.
18

Certainty of evidence of required resources – What is the certainty of the evidence of resource requirements (costs)?
The costs for medical facemasks are most probably higher than for non-medical facemasks,
and may vary greatly depending on quality, documented filtration properties, and demand.

Cost-effectiveness – Does the cost-effectiveness of the option favour the option or
the comparison?
Both the effects and the costs of facemasks are uncertain. However, with the current low
incidence of COVID-19 in Norway, the costs of using either medical or non-medical facemasks and ensuring correct use most probably outweigh the preventive effect, even if it
was assumed that the undesirable effects were minimal.

Equity – What would be the impact on health equity?
Preventive measures, if recommended, should be available and affordable for all. The priceof facemasks, whether medical or non-medical, will impact equity, as will the ability of different social groups to benefit from training programmes and use facemasks correctly.

Acceptability – Is the option acceptable to key stakeholders?
The panel believes that most people likely would find using medical or non-medical facemasks, or not using facemasks, all acceptable options, if a clear recommendation is given byauthorities with an appropriate rationale that is consistent with the available evidence andthe epidemiological circumstances.

Feasibility – Is the option feasible to implement?
Use of medical facemasks and non-medical facemasks requires training and follow-up. This
probably favours not using facemasks under the current epidemiological circumstances in
Norway.

19

Discussion and conclusion

Discussion
The use of facemasks in the community is not a substitute for other key strategies for reducing the spread of COVID-19, and should only be considered as a possible measure in addition to the core measures.
1. People infected with SARS-CoV-2 should be detected and isolated.
 People with respiratory symptoms should stay at home.
 Everyone who have symptoms of COVID-19 should be tested.
 People with COVID-19 should be in isolation until not infectious and according tonational guidelines.
 Close contacts should be traced and placed in quarantine or monitored closely andtested.
2. Everyone should continue to adhere to general mitigation measures.
 Follow good cough etiquette and hand hygiene and avoid touching your face.
 Keep a distance of at least 1 meter from everyone but your closest circle.
3. The use of facemasks by the public may be advisable in some situations.
Despite uncertainty about whether the benefits would outweigh the harms and costs, if infection rates go up or widespread community transmission occurs, facemasks should beconsidered as a precautionary measure in situations where it is difficult to adhere to social
distancing. This includes in: Public transportation like busses, trams, trains, and airplanes
 Public spaces like shops, restaurants, and communication hubs
 Mass events, like cultural, religious and sports events, and other public events, in concert halls, cinemas, sports arenas, houses of worship and public halls
The primary purpose of wearing a facemask in the community is to protect others.
The primary purpose of wearing a facemask in situations where social distancing is difficult
is for people who are infectious but do not have symptoms and do not know they are infectious to wear facemasks to prevent them from transmitting the virus to others (source control). For vulnerable populations, wearing facemasks may also protect the wearer against
infection.
The advisability of using facemasks in the community depends on the risk of infection.
The epidemiological situation plays a major role in determining when facemasks should beworn in the community. The threshold for when to recommend using facemasks in areas ofcommunity transmission depends on several factors. WHO has defined geographical areas20with community transmission as “experiencing larger outbreaks of local transmission defined through an assessment of factors including, but not limited to: large numbers of cases
not linkable to transmission chains; large numbers of cases from sentinel surveillance;
and/or multiple unrelated clusters in several areas of the country/territory/area”(https://www.who.int/publications-detail/global-surveillance-for-covid-19-caused-by-human-infection-with-covid-19-virus-interim-guidance). These are factors which NIPH is monitoring closely.
The effectiveness of facemasks depends on correct use.
If use of facemasks by individuals without respiratory symptoms in the community is recommended in specific situations, the community should be given training to ensure correct
use and the risks should be explained, especially the risks of a false sense of security andcontamination of masks. The training should be tailored to the needs of different groups,
including people with different levels of fluency in Norwegian and different socio-economic
circumstances.
The effectiveness of facemasks also depends on the type of facemask that is used.
Only medical masks and quality controlled non-medical masks with a documented filtration
effect should be used. For the preventive use for vulnerable populations medical masks arerecommended. National priorities for the use of personal protective equipment may apply,
given existing shortages. Studies of the preventive effect of facemasks in the community
are urgently needed, particularly studies of non-medical facemasks.

Conclusion
In the current epidemiological situation in Norway, wearing facemasks to reduce the spreadof COVID-19 is not recommended for individuals in the community without respiratory
symptoms who are not in near contact with people who are known to be infected. If theepidemiological situation worsens substantially in a geographical area, the use of facemasks
as a precautionary measure should be reconsidered. Measures to reduce risks during necessary public transport and during mass events, including wearing facemasks, should be explored further.
If use of facemasks by individuals without respiratory symptoms in the community is recommended in specific circumstances, such as public transport or mass events, medical
masks or quality controlled non-medical masks with a documented filtration effect should
be used. National priorities for the use of personal protective equipment may apply, given
existing shortages. If any such recommendation is made, the community should be given
training to ensure correct use and the risks should be explained, especially the risks of a
false sense of security and contamination of masks. The training should be tailored to theneeds of different groups, including people with different levels of fluency in Norwegianand different socio-economic circumstances.

Limitations
The evidence that is included was based on a rapid systematic review. Additional data werecollected from national surveillance. The aim was not to perform a systematic literature re-21view, but to provide sufficient evidence for decision making. A more detailed review process may have identified additional publications. However, for the purposes of this work,
we believe that the most relevant publications that were available were included.
The process of assessing the evidence with the EtD framework was done by an expert
panel. The panel assessed the evidence base and made a judgement for each of the criteria
in the framework. In this process, limitations of the evidence were identified and discussed.
The assessment was done by consensus, allowing each panel member to provide input tothe judgement. The judgements are reported here, making the basis for our recommendation transparent.
The panel focused primarily on the priority of the problem and the effects of the options.
The resource criteria were considered, but the evidence base was limited.
A limitation of the process is that all the panel members were employed by NIPH. We did
not invite external panel members, mainly due to limited time. Involving external panel
members could strengthen the process. It is uncertain whether this would have affected
the recommendation.

22

List of references

1. World Health Organization. Advice on the use of facemasks in the context of COVID-19.
Interim guidance 5 June 2020. https://www.who.int/publications/i/item/advice-on-theuse-of-masks-in-the-community-during-home-care-and-in-healthcare-settings-in-thecontext-of-the-novel-coronavirus-(2019-ncov)-outbreak
2. World Health Organization. Advice on the use of facemasks in the context of COVID-19.
Interim guidance 6 April 2020. www.who.int/publications-detail/advice-on-the-use-ofmasks-in-the-community-during-home-care-and-in-healthcare-settings-in-the-contextof-the-novel-coronavirus-(2019-ncov)-outbreak
3. Alonso-Coello P, Schünemann HJ, Moberg J, et al. GRADE Evidence to Decision (EtD)
frameworks: A systematic and transparent approach to making well-informed
healthcare choices. 1. Introduction. BMJ 2016; 353:i2016.
4. Moberg J, Oxman AD, Rosenbaum S, et al. GRADE Evidence to Decision (EtD) frameworks for health system and public health decisions. Health Res Policy Syst 2018;16:45.
5. Epistemonikos. Masks for Coronavirus infection. L-OVE, Coronavirus disease(COVID‑19). https://app.iloveevidence.com/loves/5e6fdb9669c00e4ac072701d?question_domain=5b1dcd8ae611de7ae84e8f14&population=5e6fdab269c00e4ac072701c&intervention=5e9c4530355258405cbec2bd
6. Epistemonikos. Search sources. Special L-OVE of Coronavirus – COVID-19. https://app.iloveevidence.com/covid-19
7. NIPH. NIPH systematic and living map on COVID-19 evidence.
https://www.nornesk.no/forskningskart/NIPH_ipcMap.html
8. NIPH. Live map of Covid-19 evidence. https://www.fhi.no/en/qk/systematic-reviewshta/map/
9. NIHR. PROSPERO International prospective register of systematic reviews.
https://www.crd.york.ac.uk/prospero/#searchadvanced
10. International Clinical Trials Registry Platform (ICTRP) https://www.who.int/ictrp/en/
11. ClinicalTrials https://clinicaltrials.gov/ct2/results?cond=COVID-19
12. Guyatt GH, Oxman AD, Akl EA, et al. GRADE guidelines 1. Introduction - GRADE evidence profiles and summary of findings tables. J Clin Epidemiol 2011; 64:383-94.
13. Whiting P, Savovic J, Higgins JPT, et al. ROBIS: A new tool to assess risk of bias in systematic reviews was developed. J Clin Epidemiol 2016; 69:225-34.

23

14. Wu H, Huang J, Zhang CJP. Facemask shortage and the coronavirus disease (COVID-19)
outbreak: Reflection on public health measures. medRxiv 2020.
http://dx.doi.org/10.1101/2020.02.11.20020735
15. Worby CJ, Chang H-H. Face mask use in the general population and optimal resource
allocation during the COVID-19 pandemic. medRxiv 2020.
http://dx.doi.org/10.1101/2020.04.04.20052696
16. Brainard JS, Jones N, Lake I, et al. Facemasks and similar barriers to prevent respiratory
illness such as COVID-19: A rapid systematic review. medRxiv 2020.
https://dx.doi.org/10.1101/2020.04.01.20049528
17. MacIntyre CR, Seale H, Dung TC, et al. A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ Open 2015; 5:e006577.
http://dx.doi.org/10.1136/bmjopen-2014-006577
18. Barr GD. A simple model to show the relative risk of viral aerosol infection and the benefit of wearing masks in different settings with implications for Covid-19. medRxiv 2020.
http://dx.doi.org/10.1101/2020.04.28.20082990
19. Ngonghala CN, Iboi E, Eikenberry S, et al. Mathematical assessment of the impact of
non-pharmaceutical interventions on curtailing the 2019 novel Coronavirus. Mathematical biosciences 2020; 325:108364. http://dx.doi.org/10.1016/j.mbs.2020.108364
20. Skarp J, Ohrnberger J, Shah H, et al. A systematic review of the direct costs and socioeconomic costs relating to non-pharmaceutical interventions against infectious disease
outbreaks. PROSPERO 2020 CRD42020177418.
https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020177418
21. Mukerji S, MacIntyre CR, Newall AT. Review of economic evaluations of mask and respirator use for protection against respiratory infection transmission. BMC Infect Dis 2015;15:413. https://doi.org/10.1186/s12879-015-1167-6
22. Houghton C, Meskell P, H. Delaney H, et al. Barriers and facilitators to healthcare workers' adherence with infection prevention and control (IPC) guidelines for respiratory infectious diseases: a rapid qualitative evidence synthesis. Cochrane Database Syst Rev
2020; 4:CD013582. https://dx.doi.org/10.1002/14651858.CD013582
23. Teasdale E, Santer M, Geraghty AWA, et al. Public perceptions of non-pharmaceuticalinterventions for reducing transmission of respiratory infection: systematic review andsynthesis of qualitative studies. BMC Public Health 2014, 14:589.
http://dx.doi.org/10.1186/1471-2458-14-589
24. Tang CS, Wong CY. Factors influencing the wearing of facemasks to prevent the severe
acute respiratory syndrome among adult Chinese in Hong Kong. Prevent Med 2004; 39:
1187-93. http://dx.doi.org/10.1016/j.ypmed.2004.04.032
25. Bundgaard H. Reduction in COVID-19 Infection Using Surgical Facial Masks Outside the
Healthcare System. ClinicalTrials.gov 7 April 2020. https://clinicaltrials.gov/ct2/show/NCT04337541

24

26. Chughtai AA, Seale H, MacIntyre CR. Use of cloth masks in the practice of infection control - evidence and policy gaps. Int J Infect Control 2013; 9:i3.
https://doi.org/10.3396/IJIC.v9i3.020.13
27. MacIntyre CR, Seale H, Dung TC, et al. A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ Open 2015; 5:e006577.
http://dx.doi.org/10.1136/bmjopen-2014-006577
28. National Academies of Sciences, Engineering, and Medicine. 2020. Rapid Expert Consultation on the Effectiveness of Fabric Masks for the COVID-19 Pandemic (April 8, 2020).
Washington, DC: The National Academies Press. https://doi.org/10.17226/25776.
29. NIPH. Situational awareness and forecasting (May 20, 2020). https://www.fhi.no/contentassets/e6b5660fc35740c8bb2a32bfe0cc45d1/vedlegg/nasjonale-rapporter/2020.05.20-corona-report.pdf

25Supplementary tables and figures

Identification

Figure S1. Flow diagram

Records identified through database searching(n = 265)

Additional records identified
through other sources(n = 20)

Screening

Duplicates(n = 22)

Records screened(n = 263)

Eligibility

Full-text articles assessed
for eligibility(n = 70)

Records excluded(n = 193)

Full-text articles excluded, withreasons(n = 22)
Non-systematic reviews – 6
Outdated systematic review - 1

Articles included(n = 48)

IncludedPrimary systematic review – 1

Commentaries – 4

Other systematic reviews – 7

Uninformative non-randomised studies – 1

Qualitative evidence syntheses – 2

Uninformative models – 4

Systematic review protocols – 16

Anecdotal evidence - 1

Randomised trial – 1
Randomised trial protocols - 2
Non-randomised studies – 4
26

Guidance – 5

Laboratory studies – 11
Models – 4

Table S1. ROBIS assessment of the primary systematic review for effects11
Domain*
1. Eligibility

Judgement†
Low

Comment
Urgency of question justifies potential lack of a protocol in a
rapid review?
No mention of protocol

1.1

NI

1.2

Y

1.3

Y

1.4

Y

1.5

Y

2. Identificationand selection
2.1

Low
Y

SCOPUS; EMBASE and Medline via OVID

2.2

Y

Two previous relevant reviews were used to find exemplar
studies. Search strategy designed to find those studies and similar research.

2.3

Y

Not guidelines, discussion, regulations, debate, or commentary

2.4

YStudies published in English since January 1980

2.5

PY

The full text of each article that passed screening was retrieved
and eligibility verified as part of data extraction (see 3)
Cochrane Rapid Reviews. Interim Guidance 2020 states that
rapid reviews should use independent risk of bias assessment.

3. Data collection
and study appraisal
3.1

Unclear

PY

Reported in synthesis section.

3.2

Y

3.3

Y

3.4

Y

RCTs assessed by Cochrane Risk of bias tool.

3.5

NSingle reviewer "Risk of bias in included RCTs was assessed (byLH)", no info on verification by second author

4. Synthesis

Low

4.1

Y

4.2

NI

4.3

Y

4.4

Y

4.5

Y

Three RCTs with total 5183 participants

4.6

Y

Addressed in GRADE and shown in SoF tables.

1 Eligibility

Low

2 Study identification and selection
3 Data collection
and study appraisal
4 Synthesis

Low
UnclearSingle reviewer assessment of risk of bias.

Low

5. RISK OF BIAS

Low

5.1

PY

5.2

Y

27

Three RCTs provide evidence on effect of wearing a mask on
respiratory infection.
No mention of protocol

The interpretation of the results appears very balanced andrisk of bias discussion seems reasonable.

5.3

Y

*The criteria used for each domain are as follows:
DOMAIN 1: STUDY ELIGIBILITY CRITERIA
1.1

Did the review adhere to pre-defined objectives and eligibility criteria?

1.2

Were the eligibility criteria appropriate for the review question?

1.3

Were eligibility criteria unambiguous?

1.4

Were any restrictions in eligibility criteria based on study characteristics appropriate (e.g. date, sample size, study quality, outcomes measured)?
1.5 Were any restrictions in eligibility criteria based on sources of information appropriate (e.g. publication status or format, language, availability of data)?
DOMAIN 2: IDENTIFICATION AND SELECTION OF STUDIES
2.1
2.2
2.3

Did the search include an appropriate range of databases/electronic sources for published and unpublished reports?
Were methods additional to database searching used to identify relevant reports?

2.4

Were the terms and structure of the search strategy likely to retrieve as many eligible studies as possible?
Were restrictions based on date, publication format, or language appropriate?

2.5

Were efforts made to minimise error in selection of studies?

DOMAIN 3: DATA COLLECTION AND STUDY APPRAISAL
3.1

Were efforts made to minimise error in data collection?

3.2
3.3

Were sufficient study characteristics available for both review authors and readers to be able to interpret the results?
Were all relevant study results collected for use in the synthesis?

3.4

Was risk of bias (or methodological quality) formally assessed using appropriate criteria?

3.5

Were efforts made to minimise error in risk of bias assessment?

DOMAIN 4: SYNTHESIS AND FINDINGS
Describe synthesis methods:
4.1

Did the synthesis include all studies that it should?

4.2

Were all pre-defined analyses reported or departures explained?

4.3
4.4

Was the synthesis appropriate given the nature and similarity in the research questions, study designs and outcomes across included studies?
Was between-study variation (heterogeneity) minimal or addressed in the synthesis?

4.5

Were the findings robust, e.g. as demonstrated through funnel plot or sensitivity analyses?

4.6

Were biases in primary studies minimal or addressed in the synthesis?

RISK OF BIAS IN THE REVIEW
Describe whether conclusions were supported by the evidence:†A

Did the interpretation of findings address all of the concerns identified in Domains 1 to 4?

B

Was the relevance of identified studies to the review's research question appropriately considered?

C

Did the reviewers avoid emphasizing results on the basis of their statistical significance?

The response options are:Y = Yes
PY = Probably yes
PN = Probably no
N = NoNI = No information

28

Table 2. Systematic reviews providing supplementary information
Reference

DOI

Bartoszko JJ, Farooqi MAM, AlhazzaniW, Loeb
M. Medical Masks vs N95 Respirators for Preventing COVID-19 in Health Care Workers A
Systematic Review and Meta-Analysis of Randomized Trials. Influenza Other Respir Viruses
2020.

https://dx.doi.org/10.1111/irv.12745

Gupta M, Gupta K, Gupta S. The use of facemasks by the general population to prevent
transmission of Covid 19 infection: A systematic review. medRxiv 2020.

https://doi.org/10.1101/2020.05.01.20087064

Jefferson T, Jones M, Ansari LAA, et al. Physical interventions to interrupt or reduce thespread of respiratory viruses. Part 1 - Facemasks, eye protection and person distancing:systematic review and meta-analysis.
medRxiv 2020.

https://dx.doi.org/10.1101/2020.04.06.20054841

MacIntyre CR, Chughtai AA. A rapid systematic review of the efficacy of face masks andrespirators against coronaviruses and otherrespiratory transmissible viruses for the community healthcare workers and sick patients.
Int J Nurs Stud 2020; NS103629.

https://doi.org/10.1016/j.ijnurstu.2020.103629

Marasinghe KM. A systematic review investigating the effectiveness of face mask use inlimiting the spread of COVID-19 among medically not diagnosed individuals: shedding lighton current recommendations provided to individuals not medically diagnosed with
COVID-19. Research Square 2020.

https://dx.doi.org/10.21203/rs.3.rs-16701/v3

Stern D, López-Olmedo N, Pérez-Ferrer C, etal. [Rapid review of the use of communitywide surgical masks and acute respiratory infections]. Salud Publica Mex 2020.

https://dx.doi.org/10.21149/11379

Zorko DJ, Gertsman S, O’Hearn K, et al. Decontamination interventions for the reuse ofsurgical mask personal protective equipment:a systematic review. OSF Preprints 2020.

https://doi.org/10.31219/osf.io/z7exu

29

Table S3. Non-randomised studies of the effects of using facemasks
Reference

DOI

Study design

Cheng VCC, Wong SC,
Chuang VWM, et al. The
role of community-widewearing of face mask forcontrol of coronavirus
disease 2019 (COVID-19)
epidemic due to SARSCoV-2. J Infect. 2020;
pii:S01634453(20)30235-8.

http://dx.doi.org/10.1016/j.jinf.2020.04.024

Ecological (country
comparison)

Hunter PR, Colon-Gonzalez F, Brainard JS,
Rushton S. Impact of
non-pharmaceutical interventions against
COVID-19 in Europe: aquasi-experimental
study. medRxiv 2020.

http://dx.doi.org/10.1101/2020.05.01.20088260

Ecological (country
comparison)

Kenyon C. Widespreaduse of face masks inpublic may slow the
spread of SARS CoV-2:
an ecological study.
medRxiv 2020.

http://dx.doi.org/10.1101/2020.03.31.20048652

Ecological (country
comparison)30

Table S4. Laboratory studies
Reference
Aydin O, Emon AB, Saif MTA. Performance of fabrics for home-made masks against spread of respiratory infection through droplets: a quantitative
mechanistic study. medRxiv 2020.
http://dx.doi.org/10.1101/2020.04.19.20071779

Bae S, Kim MC, Kin JY, et al. Effectiveness of Surgical and Cotton Masks in Blocking SARS-CoV-2: A
Controlled Comparison in 4 Patients. Ann Intern
Med 2020; M20-1342.
http://dx.doi.org/10.7326/M20-1342
Card KJ, Crozier D, Dhawan A, et al. UV Sterilization of Personal Protective Equipment with Idle
Laboratory Biosafety Cabinets During the Covid-19
Pandemic. medRxiv 2020.
http://medrxiv.org/cgi/content/short/2020.03.25.20043489
Davies A, Thompson K-A, Giri K, Kafatos G. Testing
the Efficacy of Homemade Masks: Would They
Protect in an Influenza Pandemic? Disaster Med
Pub Health Preparedness 2013; 7:413-8.
https://doi.org/10.1017/dmp.2013.43

Konda A, Prakash A, Moss GA, et al. Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks. ACS nano 2020.
http://dx.doi.org/10.1021/acsnano.0c03252

31

Key findings
The performance of ten different fabrics,
ranging from cotton to silk, in blocking highvelocity droplets, was assessed using a 3-layered commercial medical mask as a benchmark material. Breathability and ability tosoak water were also assessed. Most homefabrics substantially blocked droplets, evenas a single layer. With two layers, blocking
performance can reach that of surgical mask
without significantly compromising breathability. Home fabrics were hydrophilic to varying degrees, and hence soak water. In contrast, medical masks are hydrophobic, andtend to repel water. Incoming droplets arethus soaked and 'held back' by home fabrics,
which might be an advantage of home-madecloth masks.
Both surgical and cotton masks seemed 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.
It was calculated that an N95 mask placed
within a biosafety cabinet with a manufacturer reported fluence of 100 W/cm^2should be effectively sanitized for reuse after approximately 15-20 minutes per side.
Several household materials were evaluatedfor the capacity to block bacterial and viralaerosols in 21 healthy volunteers. The median-fit factor of the homemade masks was
one-half that of the surgical masks. Bothmasks significantly reduced the number ofmicroorganisms expelled by volunteers, although the surgical mask was 3 times more
effective in blocking transmission than thehomemade mask.
Filtration efficiencies of various commonly
available fabrics for use as cloth masks in filtering particles in the significant (for aerosolbased virus transmission) size range wasmeasured. Cotton, natural silk, and chiffon
can provide good protection, typically above
50% in the entire 10 nm to 6.0 μm range,
provided they have a tight weave. Leakages
around the mask area can degrade efficiencies by ∼50% or more, pointing out the importance of fit.

Reference
Lenormand R, Lenormand G. Effect of ethanol
cleaning on the permeability of FFP2 mask.
medRxiv 2020.
http://dx.doi.org/10.1101/2020.04.28.20083840
Leung NJL, Chu DKW, Shiu EYC, et al. Respiratory
virus shedding in exhaled breath and efficacy offace masks. Nature Med 2020; 26:676-80.
http://dx.doi.org/10.1038/s41591-020-0843-2

Ma QX, Shan H, Zhang HL, et al. Potential utilities
of mask wearing and instant hand hygiene forfighting SARS-CoV-2. J Med Virology 2020.
http://dx.doi.org/10.1002/jmv.25805

Mueller AV, Fernandez LA. Assessment of Fabric
Masks as Alternatives to Standard Surgical Masks
in Terms of Particle Filtration Efficiency. medRxiv
2020.
http://dx.doi.org/10.1101/2020.04.17.20069567
van der Sande M, Teunis P, Sabel R. Professionaland home-made face masks reduce exposure to
respiratory infections among the general population. PLoS One 2008; 3:e2618.
http://dx.doi.org/10.1371/journal.pone.0002618

Zhong H, Zhu Z, Lin J, et al. Reusable and Recyclable Graphene Masks with Outstanding Superhydrophobic and Photothermal Performance. ACS
nano 2020.
http://dx.doi.org/10.1021/acsnano.0c02250

32

Key findings
The effect of ethanol on the filtering properties of FFP2 masks was assessed. After six
cleaning cycles, the permeability remained
close to the permeability before cleaning.
In a cross-over trial, 122 of 246 participants
with medically attended acute respiratory infections were randomised to wear or not
wear a medical facemask during the first exhaled breath. Corona virus was detected in
respiratory droplets and aerosols in 3 of 10
and 4 of 10 samples collected without facemasks, respectively. No virus was detected
in respiratory droplets or aerosols collectedfrom participants wearing face masks(P=0.04).
The efficacy of three types of masks and instant hand wiping was evaluated using avian
influenza virus to mock the coronavirus. N95
masks, medical masks, and homemade
masks made of 4-layer kitchen paper and 1layer cloth could block 99.98%, 97.14%, and95.15% of the virus in aerosols.
Percent particle removal was determined forten home-made, fabric masks of different
designs. Home-made masks worn as designed always had lower particle removal
rates than the 3M masks, achieving between
38% and 96% of this baseline.
All types of masks reduced aerosol exposure,
relatively stable over time, unaffected by duration of wear or type of activity, but with ahigh degree of individual variation. Personal
respirators were more efficient than surgicalmasks, which were more efficient thanhome-made masks. Regardless of mask type,children were less well protected. Outward
protection (mask wearing by a mechanicalhead) was less effective than inward protection (mask wearing by healthy volunteers).
A method for producing commercially available surgical masks with “outstanding” selfcleaning and photothermal properties is described. Superhydrophobic states were observed on the treated masks' surfaces, which
can cause the incoming aqueous droplets tobounce off. Under sunlight illumination, thesurface temperature of the functional mask
can quickly increase to over 80 °C, making
the masks reusable after sunlight sterilization.

Table 5. Ongoing systematic reviews and randomised trials
First author, title, and ID
Randomised trials
Bundgaard H. Reduction in COVID-19 Infection Using Surgical Facial Masks Outside the Healthcare System. ClinicalTrials.gov Identifier: NCT04337541
Loeb M. Medical Masks vs N95 Respirators for COVID-19. ClinicalTrials.gov Identifier: NCT04296643
Systematic reviews
Chen M 2020. The efficacy of masks for influenza-like illness in the community, aprotocol for systematic review and metaanalysis. PROSPERO 2020
CRD42020179358
Coclite D 2020. The effectiveness of wearing face masks in the community for reducing the spread of COVID-19: a systematic review. PROSPERO 2020
CRD42020184963
Fan D 2020. N95 Respirators vs Surgical
Masks for Preventing Respiratory Infection: a systemic review and meta-analysis.
PROSPERO 2020 CRD42020172846
Gnanapragasam S. Impact of personal protective equipment (PPE) use on patient clinician interactions: a systematic review ofthe literature. PROSPERO 2020
CRD42020184693
Kirellos SA. Efficacy of different methodsof disinfection and sterilization to reusemasks and respirators: a systematic review and meta-analysis. PROSPERO 2020
CRD42020177679
Kurniawan A. The use of masks in daily life
in general public: does it affect the number of new cases and COVID-19-related
deaths? A systematic review. PROSPERO
2020 CRD42020184371
Li X. Physical interventions to reduce thetransmission of COVID-19? Lessons fromMERS and SARS. PROSPERO 2020
CRD42020178638
McNally J. Efficacy and safety of disinfectants for the decontamination of N95 andSN95 filtering facepiece respirators: protocol for a systematic review. PROSPERO
2020 CRD42020178440
McNally JD. Microwave and heat-based
decontamination for facemask personal
protective equipment (PPE). PROSPERO
2020 CRD42020177036
33

Link
https://clinicaltrials.gov/ct2/show/NCT04337541

https://clinicaltrials.gov/ct2/show/NCT04296643

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020179358

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020184963

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020172846

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020184693

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020177679

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020184371

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020178638

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020178440

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020177036

First author, title, and ID
McNally JD. Ultraviolet germicidal irradiation (UVGI) for facemask personal protective equipment (PPE): a systematic review.
PROSPERO 2020 CRD42020176156
Pezzolo E. The effectiveness of surgicalmasks vs controls in preventing of spreading respiratory infections in real life setting. PROSPERO 2020 CRD42020178913
Rajaee A. Will decontamination of N95 filtering facepiece respirators result in compromised performance? A living systematic review. PROSPERO 2020
CRD42020179695
Torres D. Efficacy of homemade and commercial cloth facemasks in preventing
COVID-19 contamination. a systematic review. PROSPERO 2020 CRD42020178007
Tran T. Efficacy of facemasks against airborne infectious diseases: a systematic review and network meta-analysis of randomized-controlled trials. PROSPERO 2020
CRD42020178516
Wu G. A systematic review and meta-analysis of the efficacy of masks for the prevention of respiratory infectious diseases.
PROSPERO 2020 CRD42020179966
Zorko D. Decontamination interventions
for the reuse of surgical mask personal
protective equipment: a systematic review. PROSPERO 2020 CRD42020178290

34

Link
https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020176156

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020178913

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020179695

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020178007

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020178516

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020179966

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020178290

Table 6. Full-text articles that were not included
Reference
Abaluck J, Chevalier J, Christakis, et al. The Case for Universal Cloth Mask Adoption& Policies to Increase the Supply of Medical Masks for Health Workers. SSRN 2020.
https://dx.doi.org/10.2139/ssrn.3567438
Bin-Reza F, Chavarrias VL, Nicoll A, Chamberland ME. The use of masks and respirators to prevent transmission of influenza: a systematic review of the scientificevidence. Influenza 2012; 6:257-67. https://doi.org/10.1111/j.17502659.2011.00307.x
Brosseau L, Sietsema M. Commentary: Masks-for-all for COVID-19 not based on
sound data. Center for Infectious Disease Research and Policy, 2020. https://publichealth.uic.edu/news-stories/commentary-masks-for-all-for-covid-19-not-basedon-sound-data/
Centers for Disease Control and Prevention. Interim Infection Prevention and Control Recommendations for Patients with Suspected or Confirmed Coronavirus Disease 2019 (COVID-19) in Healthcare settings. 13 April 2020.
https://www.cdc.gov/coronavirus/2019-ncov/hcp/infection-control-recommendations.html?CDC_AA_refVal=https%3A%2F%2Fwww.cdc.gov%2Fcoronavirus%2F2019-ncov%2Finfection-control%2Fcontrol-recommendations.html
Choi S, Ki M. Estimating the reproductive number and the outbreak size of COVID19 in Korea. Epidemiol Health 2020; 42:e2020011.
https://doi.org/10.4178/epih.e2020011
Chowell DR, Chowell G, Roosa K, et al. Sustainable social distancing through facemask use and testing during the Covid-19 pandemic.MedRxiv 2020.
https://www.medrxiv.org/content/10.1101/2020.04.01.20049981v3
Eikenberry SE, Mancuso M, Iboi E, et al. To mask or not to mask: Modelling the potential for face mask use by the general public to curtail the COVID-19 pandemic.
Infect Dis Modelling 2020; 5:293-308. https://doi.org/10.1016/j.idm.2020.04.001
Fan J, Liu X, Pan W, et al. Epidemiology of 2019 novel coronavirus disease in Gansu
Province, China, 2020. Emerg Infect Dis 2020.
https://doi.org/10.3201/eid2606.200251
Greenhalgh T, Schmid MB, Czypionka T, et al. Face masks for the public during thecovid-19 crisis. BMJ 2020; 369:m1435. https://doi.org/10.1136/bmj.m1435
Howard J, Huang A, Tufekci Z, et al. 2020 Face masks against COVID-19: An evidence review. Preprints 2020, 2020040203. https://dx.doi.org/10.20944/preprints202004.0203.v1
Juneau C-E, Pueyo T, Bell M, et al. Evidence-based, cost-effective interventions tosuppress the COVID-19 pandemic: a rapid systematic review. medRxiv 2020.
https://doi.org/10.1101/2020.04.20.20054726
Leung CC, Lam TH, Cheng KK. Mass masking in the COVID-19 epidemic:people
need guidance. Lancet 2020; 395:945. https://dx.doi.org/10.1016/s01406736(20)30520-1
Liu X, Zhang S. COVID-19: Face Masks and Human-to-human Transmission. Influenza 2020. https://doi.org/10.1111/irv.12740
Madhav N, Oppenheim B, Gallivan M, et al. Pandemics: Risks, impacts, and mitigation. In: Jamison DT, Gelband H, Horton S, et al., editors. Disease Control Priorities:
Improving Health and Reducing Poverty. 3rd edition. Washington DC: The International Bank for Reconstruction and Development / The World Bank; 2017.
https://dx.doi.org/10.1596/978-1-4648-0527-1/pt5.ch17
Norwegian Institute of Public Health. Coronavirus – facts, advice and measures.
Hand hygiene, cough etiquette, facemasks, cleaning and laundry - Advice and information to the general public. 22 April 2020. www.fhi.no/en/op/novel-coronavirus-facts-advice/facts-and-general-advice/hand-hygiene-cough-etiquette-facemasks-cleaning-and-laundry/
35

ReasonCommentary
Outdatedsystematic
review
Commentary

Guidance

Uninformative* model
Uninformative model
Uninformative model
Uninformative nonrandomised
study
CommentaryNon-systematic review
Broad overview
Commentary
Anecdotal
evidence
Non-systematic review

GuidanceReference
Van Hylckama Vlieg A, Rosendaal F, Mook-Kanamori D. FFP2-mondmasker of chirurgisch mondkapje bij COVID-19. 0 Huisarts en Wetenschap 2020.
https://dx.doi.org/10.1007%2Fs12445-020-0586-9
Vannabouathong C, Devji T, Ekhtiari S, et al. Novel Coronavirus COVID-19: current
evidence and evolving strategies. J Bone Joint Surg 2020; 102:734-44.
https://dx.doi.org/10.2106/JBJS.20.00396
National Academies of Sciences, Engineering, and Medicine. 2020. Rapid Expert
Consultation on the Effectiveness of Fabric Masks for the COVID-19 Pandemic(April 8, 2020). Washington, DC: The National Academies Press.
https://doi.org/10.17226/25776
Royal Society. Face masks for the general public. Royal Sciety DELVE Initiative
2020. https://rs-delve.github.io/reports/2020/05/04/face-masks-for-the-generalpublic.html
World Health Organization. Advice on the use of facemasks in the context of
COVID-19. Interim guidance 6 April 2020. www.who.int/publications-detail/adviceon-the-use-of-masks-in-the-community-during-home-care-and-in-healthcare-settings-in-the-context-of-the-novel-coronavirus-(2019-ncov)-outbreakWorld Health Organization. Infection prevention and control guidance for longterm care facilities in the context of COVID-19. WHO 2020; WHO/2019nCoV/IPC_long_term_care/2020.1 https://apps.who.int/iris/handle/10665/331508
World Health Organization. Rational use of personal protective equipment forcoronavirus disease (COVID-19) and considerations during severe shortages. Interim guidance 6 April 2020. https://apps.who.int/iris/bitstream/handle/10665/331695/WHO-2019-nCov-IPC_PPE_use-2020.3-eng.pdf

36

ReasonNon-systematic review
Non-systematic review
Non-systematic review
Non-systematic review
Guidance

Guidance

Guidance

Figure S2
Summary of Findings table from Brainard and colleagues [Brainard 2020]). This figure isavailable under a CC-BY-ND 4.0 International license)

37

Figure S3 from Brainard and colleagues [Brainard 2020]). This figure is available under a CCBY-ND 4.0 International license)

38

Figure S4from Brainard and colleagues [Brainard 2020]). This figure is available under a CCBY-ND 4.0 International license)39

Appendix. Updated search 9 June 2020

In addition to daily L-OVE updates, checking reference lists of full-text articles that arescreened, and articles identified through personal communication, the Cochrane COVID-19
Study Register was screened May 23rd using the term “masks”, which yielded 35 records
and one included study [Matusiak 2020]. Four rapid evidence profiles from the McMaster
Health Forum were also screened [McMaster 2020a-d].
Fourteen full-text articles were screened, seven were included (Table 1) and seven were excluded (Table 2).
Table 1. Included articles
Systematic reviews providing supplementary information
Chu DK, Akl EA, Duda S, et al. Physical distancing, facemasks, and eye protection to prevent person-to-persontransmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis. Lancet 2020.
https://doi.org/10.1016/S0140-6736(20)31142-9

Lee KM, Shukla VK, Clark M, et al. physical interventions to interrupt or reduce the spread of respiratory viruses — resource use implications: a systematic review.
Ottawa: Canadian Agency for Drugs and Technologies
in Health; 2011. http://www.cadth.ca/en/products/healthtechnology-assessment/publication/3140

Liang M, Gao L, Cheng C, et al. Efficacy of face mask inpreventing respiratory virus transmission: a systematic
40

This review included 30 studies of the association
between use of various types of face masks andrespirators by health-care workers, patients, orboth withtransmission of COVID-19, SARS, or MERS. 10
studies contributed data to a meta-analysis of adjusted associations. The estimated OR for surgicalfacemask or similar (e.g., 12–16-layer cotton) vs
no facemask was 0.33 (95% CI 0.17 to 0.61).
However, only one study of primary prevention in
the community was included [Wu 2004], which
was also included in the Brainard review [Brainard
2020] and was considered in our review. The review authors assessed the certainty of the evidence for facemasks vs no facemasks as low
overall for any setting without distinguishing between primary and secondary prevention or considering non-medical facemasks. The estimate isvery uncertain for the use of masks in the community for primary prevention, especially for nonmedical facemasks. It is likely an overestimate,because compliance with correct use would likely
be lower and non-medical facemasks are likely tobe less effective.
This review included 7 non-randomised economic
studies that were judged to provide very low certainty evidence. The studies all found that use of
personal protective equipment was economicallyattractive. However, the results were sensitive toassumptions about rate of transmission, facility infection rate, and compliance with interventions,with economic attractiveness increasing whentransmission and fatality rates are high.
This review included 21 studies of mask use toprevent respiratory virus transmission. It did notreview and meta-analysis. medRxiv 2020.
https://doi.org/10.1101/2020.04.03.20051649

Saijonkari M, Booth N, Isojärvi J, Finnilä J, Mäkelä M.
Kasvosuojukset COVID-19-tartunnalta suojautumisessa
ja infektioepidemian hallinnassa: järjestelmällinen
katsaus ja näytön arviointi. (Face masks in preventing
COVID-19 infections and controlling the epidemic.) (InFinnish). In: Report on the use of community face coverings to prevent the spread of the COVID-19 epidemic.
Reports and Memorandums of the Ministry of Social Affairs and Health 2020:21, Appendix 1.
http://urn.fi/URN:ISBN:978-952-00-5421-2

include any non-healthcare worker studies thatwere not included in Bainard 2020. The estimated
OR for mask use vs control for non-healthcare
workers was 0.53 (95% CI 0.36 to 0.79). Therewas variation in the effect estimates (I2 = 45%)
and a subgroup difference between healthcare
workers and non-healthcare workers (P=0.008),
with a stronger association for healthcare workers(OR 0.20; 95% CI 0.11 to 0.37).. There were also
subgroup differences for different viruses (influenza, SARS-CoV an SARS-CoV2) (P=0.002), anddifferent study designs (P=0.0002). Cluster-randomised studies indicated a smaller effect (OR0.65; 95% CI 0.47 to 0.91) and case-control studies indicated the largest effect (OR 0.24; 95% CI
0.18 to 0.33).
This review included six systematic reviews andsix randomised trials. Four of the six RCTs were
included in the Brainard review [Brainard 2020].
Saijonkari et al. did not conduct a meta-analysis.
None of the included studies examined use of
facemasks in a situation similar to the normal living environment of the Finnish population. The review assessed safety and found that facemasks
appear to cause discomfort to users, but not actual harm. This review concluded that the effect of
facemasks used outside the home on the spreadof droplet-mediated respiratory infections in the
population is minimal or non-existent

Laboratory studies
Reference

Key findings

Chan JF-W, Yuan S, Zhang AJ, et al. Surgical mask
partition reduces the risk of non-contact transmission 1
in a golden Syrian 2 hamster model for Coronavirus Disease 2019 (COVID-19). Unpublished manuscript 18
May 2020.

Transmission from a hamster infected with
COVID-19 to hamsters in separate cages was investigated under three conditions: without a surgical mask partition between the cages, with a surgical mask partition with the outside facing the uninfected hamsters (simulating the infected hamsters wearing a mask), and with the outside facing
the infected hamster (simulating the uninfected
hamsters wearing a mask). Without a surgicalmask partition 10 of 15 hamsters (67%) were infected. When the cages were separated by a surgical mask partition with the outside facing the uninfected hamsters, 2 of 12 hamsters (17%) were
infected (P=0.019). When the outside of the surgical mask partition with the outside facing the infected hamster, 4 of 12 hamsters (33%) were infected (P=0.128).

Non-randomised studies
Reference

Key findings

Matusiak L, Szepietowska M, Krajewski P, et al. Inconveniences due to the use of face masks during the
COVID-19 pandemic: a survey study of 876 young people. Dermatologic Therapy 2020.
https://doi.org/10.1111/dth.13567

Out of 876 students in Poland who participated ina survey only 27 people (3%) did not complain ofany problems related to face mask wearing. Out of
all reported inconveniences, difficulty in breathingappeared to the most common one (36%), followed by warming/sweating (21%), misting up of41

Mitze T, Kosfeld R, Rode J, Wälde K. Face masks considerably reduce COVID-19 cases in Germany: a synthetic control method approach. IZA Institute of Labor
Economics Discussion Paper Series 2020; IZA DP No.
13319. http://ftp.iza.org/dp13319.pdf

glasses (21%) and slurred speech (12%). Skin reactions were reported less often (itch - 7.7%, skinirritation - 0.9%). Wearing surgical masks compared to other types of masks had a lower risk for
difficulty in breathing, warming/sweating, glasses
misting up, slurred speech and itch (OR=0.42,
OR=0.60, OR=0.10, OR=0.17 and OR=0.04, respectively). Wearing cloth masks had a higher riskof difficulty in breathing (OR=1.56), warming/sweating (OR=1.31), glasses misting up(OR=1.92), slurred speech (OR=1.86) and itch
(OR=2.99).
This study compares infection rates in the city ofJena, Germany where facemasks were introducedon 6 April 2020 to other areas in Germany where
facemasks were not introduced until later using a
synthetic control, i.e. using a weighted combination of infection rates in other areas as the control
to which infection rates in Jena were compared inregression analyses. The study estimates thatface masks reduced the cumulative number ofregistered Covid-19 cases between
2.3% and 13% over a period of 10 days after they
became compulsory and that the daily increase inreported infections was reduced by around 40%.

Table 2. Excluded articles
Reference

ReasonClase CM, Fu EL, Joseph M, et al. Cloth masks may prevent transmission of covid-19: an evidencebased, risk-based approach. Ann Intern Med 2020; https://doi.org/10.7326/M20-2567
ECRI. Cloth face coverings worn by public to reduce transmission of viral respiratory infection. Clinical
Evidence Assessment 2020. https://www.ecri.org/covid-19-clinical-evidence-assessments
European Centre for Disease Prevention and Control. Using face masks in the community. Stockholm:
ECDC; 2020. https://www.ecdc.europa.eu/en/publications-data/using-face-masks-community-reducing-covid-19-transmission
Feng S, Shen C, Xia N, et al. Rational use of face masks in the COVID-19 pandemic. Lancet Respir
Med 2020; 8:436-8. https://doi.org/10.1016/S2213-2600(20)30167-3
Government of Canada. Non-medical masks and face coverings: about. 24 May 2020.
https://www.canada.ca/en/public-health/services/diseases/2019-novel-coronavirus-infection/prevention-risks/about-non-medical-masks-face-coverings.html
Marin T. Evidence summary. respiratory infection transmission (community): face masks and respirators. The Joanna Briggs Institute EBP Database, JBI@Ovid. 2020; JBI23909.
https://jbi.global/sites/default/files/2020-04/23909%20%2823937%29%20Respiratory%20Infection%20Transmission%20%28Community%29%20Face%20Masks%20and%20Respirators%20%28AS-1%29.pdf
Ontario Health. Priority Setting of Personal Protective Equipment – Within Health Care Institutions andCommunity Support Services. Ethics Table Policy Brief #3, 25 March 2020. https://www.wrh.on.ca/uploads/Coronavirus/Ethics_Table_Policy_Brief_3_PPE_Within_Health_Care_Institutions_Community_Support_Services.pdf

CommentaryNon-systematic
review
Guidance
Guidance
Guidance
Non-systematic
review

Ethical considerations

References[Brainard 2020] Brainard JS, Jones N, Lake I, et al. Facemasks and similar barriers to prevent respiratory illness such as COVID-19: A rapid systematic review. medRxiv 2020.
https://dx.doi.org/10.1101/2020.04.01.20049528

42

[Matusiak 2020] Matusiak L, Szepietowska M, Krajewski P, et al. Inconveniences due to the use offace masks during the COVID-19 pandemic: a survey study of 876 young people. Dermatologic Therapy 2020. https://doi.org/10.1111/dth.13567[McMaster 2020a] Wilson MG, Gauvin FP, Waddell K, et al. COVID-19 rapid evidence profile #1:
What is known aboutapproaches to and safety of conserving, re-using, and repurposing different
kinds of masks? Hamilton: McMaster Health Forum, 14 April 2020. https://www.mcmasterforum.org/docs/default-source/covidend/rapid-evidence-profiles/covid-19-rep1_ppe.pdf?sfvrsn=52a657d5_4[McMaster 2020b] Wilson MG, Gauvin FP, Moat KA, et al. COVID-19 rapid evidence profile #4: What
are the most effective non-medical masks for preventing community transmission of COVID-19, andshould they be required for all of society? Hamilton: McMaster Health Forum, 29 April 2020.
https://www.mcmasterforum.org/docs/default-source/covidend/rapid-evidence-profiles/covid-19rep-4_non-medical-masks.pdf?sfvrsn=73bd57d5_2[McMaster 2020c] Waddell K, Gauvin FP, Wilson MG, et al. COVID-19 rapid evidence profile #5: Whatis known about the use of medical masks by essential non-medical workers to prevent community
transmission of COVID-19? Hamilton: McMaster Health Forum, 29 April 2020. https://www.mcmasterforum.org/docs/default-source/covidend/rapid-evidence-profiles/covid-19-rep-5_medicalmasks_2020-04-29_final.pdf?sfvrsn=99be57d5_2[McMaster 2020d] Waddell K, Wilson MG, Gauvin FP, et al. COVID-19 rapid evidence profile #6:
What is known about strategies for supporting the use of masks under shortage conditions to prevent COVID-19? Hamilton: McMaster Health Forum, 30 April 2020. https://www.mcmasterforum.org/docs/default-source/covidend/rapid-evidence-profiles/covid-19-rep6_masks.pdf?sfvrsn=21bf57d5_2[Wu 2004] Wu J, Xu F, Zhou W, et al. Risk factors for SARS among persons without known contact
with SARS patients, Beijing, China. Emerg Infect Dis 2004; 10:210-6.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3322931/

43

Published by the Norwegian Institute of Public HealthJune 2020
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NO-0213 Oslo
Tel: +47 21 07 70 00
www.fhi.no