who -COVID-19 infection prevention and control living guideline - mask use in community settings,22 December 2021-此为英文文档

COVID-19

InfectionPreventionandControl

Livingguideline

Maskuseincommunitysettings

22December2021

WorldHealth

•Organization

WHOInfectionPreventionandControlCOVID-19LivingGuideline-Maskuseincommunitysettings-WorldHealthOrganization(WHO)

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Sections

1.

ExecutiveSummary 3

1.1

Abbreviations 3

1.2

Definitions 4

2.

Methodology 5

3.

Advice,statementsandrecommendations 7

3.1

Generalmaskadvice 7

3.2

Maskuseincommunitysettings 7

3.2.1

Maskuseduringphysicalactivity 15

3.2.2

Typeofmaskusedbythegeneralpublic 16

3.3

Maskusebychildren 22

4.

Acknowledgements 29

References 31

WHOcontinuestomonitorthesituationcloselyforanychangesthatmayaffectthislivingguideline.Shouldanyfactorschange,WHOwillissueafurtherupdate.Otherwise,thislivingguidelinewillexpire2yearsafterthedateofpublication.

©WorldHealthOrganization2021.Somerightsreserved.Thisworkisavailableunderthe

CCBY-NC-SA3.0IGOlicence

.WHOreferencenumber:WHO/2019-nCoV/IPC_masks/2021.1

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1.ExecutiveSummary

InfoBox

Version1.0InfectionPreventionandControlinthecontextofcoronavirusdisease(COVID-19):LivingGuideline

ThisfirsteditionoftheInfectionPreventionandControlinthecontextofcoronavirusdisease(COVID-19):LivingGuidelineprovidesthemostuptodatetechnicalguidanceonmaskuseincommunitysettingsinthecontextofCOVID-19.ThislivingguidelineincorporatestheGradingofRecommendations,Assessment,DevelopmentandEvaluations(GRADE)processes(seeMethodologysection)withexisting(previouslypublished)technicalguidanceinMAGICapptoallowuserstoeasilynavigateinfectionpreventionandcontrol(IPC)guidelinesinthedynamicsituationofCOVID-19.Thiseditiontakesintoconsiderationtheevolvingepidemiologicalsituation,includingtheemergenceoftheVoCOmicron.FurtherinformationonOmicronVoCcanbefoundinthefollowingtechnicaldocumentEnhancingReadinessforOmicron(B.1.1.529):TechnicalBriefandPriorityActionsfortheMemberStates,issuedbyWHOon17December2021[1].

Thisdocumentisalivingguideline,whereupdatedornewstatementswillbeaddedasnewevidenceemergesthatwillbereviewedthroughtheGRADEprocess.Thus,theguidelineiswritten,disseminated,andupdatedinMAGICapp.Itsuser-friendlyformatandstructureallowforeasynavigationwhileaccommodatingforthedynamicnatureoftheCOVID-19publichealthemergencyandassociatedevidenceandrecommendations.MAGICAppallowshighlightingofnewandupdatedstatementswhilekeepingexistingstatementsandsupportingevidencewithintheguideline.Thestatementsaremarkedwithdifferentlabelsandcolourcodingtoreflectthedifferentconsolidationapproachesofexistingguidance,updates,andnewstatements.

Inthisedition,newinformationincludesupdatedmaskrecommendationsforthegeneralpublic,astatementonpoliciesforappropriateadherencetoacomprehensivepackageofpreventivemeasurestoreducesevereacuterespiratorysyndromecoronavirus2(SARS-CoV-2)transmission,astatementonthetypeofmasktobeusedbyhigher-riskindividuals,andimplementationconsiderationsforthetypeandminimumessentialparametersofmasksusedincommunitysettings.

ThepreviouslypublishedtechnicalguidancedocumentsincorporatedinVersion1.0areasfollows:

1.

MaskuseinthecontextofCOVID-19-December2020

;and

2.

AdviceontheuseofmasksforchildreninthecontextofCOVID-19

-August2020;.

TheWorldHealthOrganization(WHO)recommendstheuseofmasksaspartofacomprehensivepackageofpreventionandcontrolmeasurestolimitthespreadofSARS-CoV-2,thevirusthatcausesCOVID-19.Evenwhenusedcorrectly,amaskaloneisinsufficienttoprovideadequateprotectionorsourcecontrol.Otherpublichealthandsocialmeasuresincludetesting,isolation,contacttracing,quarantine,adequateventilationinindoorsettings,aphysicaldistancingofatleast1metre,handhygiene,andrespiratoryetiquette.Together,thesemeasuresarecriticaltopreventhuman-to-humantransmissionofSARS-CoV-2.Thisdocumentguidesdecision-makers,publichealthandIPCprofessionals,childhealthprofessionalsandnon-medicalmaskmanufacturers.

1.1Abbreviations

aOR

adjustedoddsratio

COVID-19

coronavirusdisease2019

CI

ConfidenceInterval

EtD

EvidencetoDecision

GDG

GuidelineDevelopmentGroup

GRADE

GradingofRecommendations,Assessment,DevelopmentandEvaluations

ILI

Influenza-likeillness

IPA

InternationalPaediatricAssociation

IPC

infectionpreventionandcontrol

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NIOSH

NationalInstituteforOccupationalSafetyandHealth

OR

oddsratio

PPE

personalprotectiveequipment

SARS-CoV

severeacuterespiratorysyndromecoronavirus

SARS-CoV-2

severeacuterespiratorysyndromecoronavirus2

UNICEF

UnitedNationsChildren'sFund

UK

UnitedKingdom

USA

UnitedStatesofAmerica

WHO

WorldHealthOrganization

VoC

VariantofConcern

1.2Definitions

Definitions

Healthworkersareallpeopleprimarilyengagedinactionswiththeprimaryintentofenhancinghealth.Examplesarenursingandmidwiferyprofessionals,doctors,cleaners,otherstaffwhoworkinhealthfacilities,socialworkersandcommunityhealthworkers.

Medicalmasksaredefinedassurgicalorproceduremasksthatareflatorpleated,andtheyareaffixedtotheheadwithstrapsaroundtheears,head,orboth.Theirperformancecharacteristicsaretestedaccordingtoasetofstandardizedtestmethods(ASTMF2100,EN14683,orequivalent)thataimtobalancehighfiltration,adequatebreathabilityand,optionally,fluidpenetrationresistance[5][121].

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2.Methodology

Methodologyfordevelopingthestatements

StatementsincludedinthisdocumentarebasedonpublishedWHOguidelines(inparticular,theWHOGuidelinesoninfectionpreventionandcontrolofepidemic-andpandemic-proneacuterespiratoryinfectionsinhealthcare)andongoingevaluationsofallavailablescientificevidencebyWHOCOVID-19IPCGuidanceDevelopmentGroup(GDG)(seeAcknowledgements).Thisevidenceisevaluatedthroughexpeditedsystematicreviewsandexpertconsensus-buildingthroughregularGDGconsultationsfacilitatedbyamethodologist.Whenfurtherclarityorconsensusisnecessary,meetingsarefollowedupbyavotingprocessbytheGDGmembers.Recommendationsarebasedonanassessmentofthebalanceofbenefitstoharmsaswellascertaintyintheseassessments.Thisprocessalsoconsiders,asmuchaspossible,potentialresourceimplications,valuesandpreferences,feasibility,equityandethics.Anexternalreviewpanelofexpertsreviewsdraftguidancedocumentsbeforepublication.

Methodologyfordevelopingthislivingguideline

Asdescribedintheexecutivesummary,giventhedynamicsituationoftheCOVID-19pandemic,thisfirsteditionofthislivingguidelinecombinesexistingguidanceformulatedthroughexpertreviewofevidence,theGRADEevidence-to-decision(EtD)framework,andstandardsfortrustworthyguidelines.ForrecommendationsfollowingtheGRADEEtDframework,aGDGcomprisedofindividualswithbroadexpertisespanningmultiplespecialtiesacrossallWHOregions(seeAcknowledgements)wasconvenedovermultiplemeetingswhereGDGmembersreachedagreement(throughconsensusorvotewithsupermajority)onthestatements.

ManagingConflictsofInterest

AfteranalyzingtheDeclarationofInterestformsandconductingtherequiredinternetsearch,WHOconcludednomemberhadfinancialorcommercialinterestsrelatedtoCOVID-19andmasks.Methodsarealignedwith

WHOHandbookforguidelinedevelopment

.

Readershipcuesforapproachesusedtodevelopstatements

Giventheconsolidationprocess,thestatementsaremarkedwithdifferentlabelsandcolourcodestoreflectthesetwoapproaches.ThegreencheckmarksreflectstatementsthatweredevelopedusingtheGRADEEtDframework.PurplecheckmarksrefertostatementsthathavenotgonethroughtheGRADEEtDframeworkprocessbutareinformedbyevidencereviewandaretheproductofexpertconsensus.Thegreybarreferstoimplementationconsiderationswhichsupportstatementsthroughpracticaladvice,andaretheproductofexpert

consensus.

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GRADEEtDFramework

GRADEratesscientificevidencetodevelopevidence-basedguidelines.Eachrecommendationisassignedastrengthofrecommendationandqualityofevidence.

GRADEevidenceprofilescontainanassessmentofthequalityoftheevidenceandasummaryoffindingsforeachcriticaloutcomeandeachkeyquestion.TheGDGusesthesesummariesasthebasisfordiscussionsandformulationofrecommendations.

Goodpracticestatementsandimplementationconsiderations

Goodpracticestatementsindicateactionsthatshouldbeimplemented,inmostcircumstances,whenthecertaintysurroundingtheeffectestimatesishigh,butthesupportiveevidenceisindirect.Benefitsarebasedonmultiplebodiesofindirectevidence,oftenchallengingtoreviewsystematically.Goodpracticestatementsaregenerallyreservedforconsiderationswithwidespreadconsensusandwhentheinterventioniswidelyaccepted.Implementationconsiderationsarecriticalelementsthatfacilitatetheappropriateuseofformalstatements.

Timeline

AnexternallivingsystematicreviewhasbeencommissionedtocontinuouslymonitoremergingevidenceontheuseofmasksinthecontextoftheCOVID-19publichealthemergencyofinternationalconcern.Theemergingevidencewilltriggercontinuousupdatesastheneedisidentified.

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3.Advice,statementsandrecommendations

3.1Generalmaskadvice

InfoBox

Maskmanagement

Foranytypeofmask,appropriateuse,storage,cleaningordisposalareessentialtoensurethattheyareaseffectiveaspossibleandtoavoidanyincreasedriskoftransmission.Adherencetocorrectmaskmanagementpracticesvaries,reinforcingtheneedforappropriatemessaging[115].WHOprovidesthefollowingguidanceonthecorrectuseofmasks:

•Washhandsthoroughlybeforeputtingonthemask.

•Inspectthemaskfortearsorholes,anddonotuseadamagedmask.

•Placethemaskcarefully,ensuringitcoversthemouthandnose,adjusttothenosebridgeandtieitsecurelytominimizeanygapsbetweenthefaceandthemask.Ifusingearloops,ensurethesedonotcrossoverasthiswidensthegapbetweenthefaceandthemask.

•Avoidtouchingthemaskwhilewearingit.Ifthemaskisaccidentlytouched,washhandsthoroughly.

•Removethemaskusingtheappropriatetechnique.Donottouchthefrontofthemask;rather,untieitfrombehind.

•Replacethemaskassoonasitbecomesdampwithanew,cleananddrymask.

•Eitherdiscardthemaskorplaceitinacleanplasticresealablebagwhereitiskeptuntilitcanbewashedandcleaned.Donotstorethemaskaroundthearmorwristorpullitdowntorestaroundthechinorneck.

•Washhandsimmediatelyafterdiscardingamask.

•Donotreusesingle-usemasks.

•Discardsingle-usemasksaftereachuseandproperlydisposeofthemimmediatelyuponremoval.

•Donotremovethemasktospeak.

•Donotshareyourmaskwithothers.

•Washfabricmasksinsoapordetergentandpreferablyhotwater(atleast60°Centigrade/140°Fahrenheit)atleastonceaday.Ifitisnotpossibletowashthemasksinhotwater,thenwashthemaskinsoap/detergentandroom-temperaturewater,followedbyboilingthemaskfor1minute.

•Amaskshouldbechangedtoacleanmaskatleastoncedaily.

Extractedfromtheguidancetitled“MaskuseinthecontextofCOVID-19”,published1December2020.

Exhalationvalvesonrespiratorsandnon-medicalmasksarediscouragedastheydonotallowforadequatesourcecontrolfromthewearer.Exhalationvalvespermitbypassofthefiltrationlayerswhenthewearerexhales,potentiallyallowingpass-throughofinfectiousparticles.

Extractedfromtheguidancetitled“MaskuseinthecontextofCOVID-19”,published1December2020.

3.2Maskuseincommunitysettings

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InsettingswherethereiscommunityorclustertransmissionofSARS-CoV-2

Updated

Strongrecommendationfor,Moderatecertaintyevidence

InsettingswherethereiscommunityorclustertransmissionofSARS-CoV-2,irrespectiveofvaccinationstatusorhistoryofpriorinfection,wearingawell-fittingmask*thatcoversthenoseandmouthisrecommendedforthegeneralpublicwheninteractingwithindividualswhoarenotmembersoftheirhousehold:

•inindoorsettingswhereventilationisknowntobepoororcannotbeassessed,ortheventilationsystemisnotproperlymaintained,regardlessofwhetherphysicaldistancingofatleast1metrecanbemaintained1;

•inindoorsettingsthathaveadequateventilationifphysicaldistancingofatleast1metrecannotbemaintained*;or

•inoutdoorsettingswherephysicaldistancingofatleast1metrecannotbemaintained*.

*Masktypesinclude:

•reusable,non-medicalmasksthatcomplywiththe

ASTMF3502

standardor

CENWorkingAgreement17553

,oranon-medicalmaskmeetingWHOessentialparameters(seepracticalinfoformoreinformation).;

•disposablemedicalmasks,complyingwithmedicalmaskstandardsEN14683TypeI,ASTMF2100Level1,YY/T0969,YY0469(orequivalent)iftheavailabilityofmedicalmasksmeetingminimumperformancecriteriaforhealthworkershasbeenassured**;

•iftheaboveoptionsarenotavailable,othertypesofwell-fittingnon-medicalmasksincludinghomemademultilayeredmasks***areanacceptableoption(accordingtolocalpolicies).

1Physicaldistanceshouldbeincreasedbeyond1metrewheneverfeasible.

Updated22December2021.

PracticalInfo

Forinformationonassessingandimprovingindoorventilation,pleaseseeWHO's

Roveensureg

oadmaptoimprandoodindoor

venconoCOVID-19

tilationinthetextf.

Practicalconsiderationsforpolicy-makers:

Thepotentialadvantagesofmaskusebyhealthypeopleinthegeneralpublicinclude:

•reducedspreadofpotentiallyinfectiousaerosolsordropletsfromexhaledbreath,includingfrominfectedpeoplebeforetheydevelopsymptoms[15];

•encouragingconcurrenttransmissionpreventionbehaviourssuchaswashinghandsandnottouchingtheeyes,noseandmouth[16][17][18];and

•preventingtransmissionofotherrespiratoryillnessessuchastuberculosisandinfluenzaandreducingtheburdenofthesediseasesduringthepandemic[19].

Thepotentialdisadvantagesofmaskusebyhealthypeopleinthegeneralpublicinclude:

•headacheand/orbreathingdifficulties,dependingonthetypeofmaskused[12];

•developmentoffacialskinlesions,irritantdermatitisorworseningacnewhenusedfrequentlyforlonghours[13][20];

•difficultywithcommunicatingclearly,especiallyforpersonswhoaredeaforhavepoorhearingoruselipreading[21][22];

•poorcompliancewithmask-wearing,inparticularbyyoungchildren[24][25][26][27];

•wastemanagementissues;impropermaskdisposalleadingtoincreasedlitterinpublicplacesandenvironmentalhazards[28];and

•furtherdisadvantagesfor,ordifficultywearingmasksby,certainmembersofthepopulation,especially:children;

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developmentallychallengedpeople;thosewithmentalillnessorcognitiveimpairment;thosewithasthma,chronicrespiratoryorbreathingproblems;thosewhohavehadfacialtraumaorrecentoralmaxillofacialsurgery;andthoselivinginhotandhumidenvironments[12][25].

EvidenceToDecision

Benefitsandharms

Substantialnetbenefitsoftherecommendedalternative

TheutilizationofmasksincommunitysettingsislikelyassociatedwithadecreasedriskofSARS-CoV-2infectionscomparedwithnomask-wearing.SARS-CoV-2B.1.617.2(Delta)varianthasbeenreportedtohaveincreased

transmissibility[29][30][31][33][32];mostGDGmembers,therefore,agreedthat,inthecontextoftheDeltavariant,thebenefitsofmask-wearinginthecommunitysettingoutweighpotentialharms.EcologicalstudieshaveidentifiedanassociationwithdecreasednumberofconfirmedcasesofCOVID-19andpoliciesrequiringtheuseofmasks[34][35][36].Aclusterrandomizedcontrolledtrialevaluatingmaskpromotion(asanindirectpublichealthintervention)foundthatinacountrywithlowmaskuse,maskpromotionincreasedmaskuseanddecreasedsymptomaticSARS-CoV-2seroprevalence[37].Conversely,anotherrandomizedcontrolledtrialfoundnostatisticalsignificanceassociatedwithsurgicalmaskuseandareducedriskofSARS-CoV-2[38].Thestudyprovidedanimpreciseestimateformaskutilizationversenoutilization;however,thestudywasnotdesignedtoevaluatetheeffectivenessofmaskuseforsourcecontrol.

ManyGDGmembersnotethat,eventhoughthecertaintyoftheevidenceismoderate,thereisasubstantialneedforWHOtoproducecohesiveandrobustrecommendations,asthenetbenefitsofmaskusebythegeneralpublicoutweighthepotentialharms.

Moderate

CertaintyoftheEvidence

Balanceofdesirableandundesirableoutcomes.

Preferenceandvalues

Nosubstantialvariabilityexpected

DiscussionswithstakeholdersandIPCGDGmembershaveindicatedageneralpreferencetofavourmaskuseincommunitysettings.ManyGDGmembersnotethat,inthecontextoftheDeltavariantandothervariantsofconcern,maskingisavitalSARS-CoV-2mitigationmeasure.Membersexpressedaneedtodocumentaclearopinionontheuseofmasksincommunitysettings,giventheimpactoflocalandnationalvaluesandpreferencesonIPCpolicies.Giventheavailabilityofmasks,communitymaskingislikelyfeasible.

Resourcesandotherconsiderations

Noimportantissueswiththerecommendedalternative

ManyGDGmembersnotedtheglobalsupplychainformaskmanufacturinghasimprovedandwouldnotposeasevereobstacletocommunitymasking.Thecostofbothmedicalmasksandnon-medical(fabric)masksarerelativelylow,anddonotposeasubstantialbarrierforlow-andmiddle-incomecountries.

Gapsinknowledgeandresearchneeds

Investigationsontheutilizationofmasksinthecommunitysettingareongoing;however,publishedworkhasidentifiedtheneedforcontinuedresearch.Wellconductedobservationalstudiesand/orrandomizedcontrolledtrialsexploringtheuseofmasksversusnomasksinvarioussettings(e.g.indoor,outdoor,ventilationstatus,etc.)wouldfurtherclarifyoutstandinginquiriesconcerningmaskuseincommunitysettings.Inaddition,researchinvestigatingtheuseofmasks(includingtypeofmaskandtransmissionscenarios)inthecontextoftheDeltavariantwouldprovidepowerfulevidenceforfuturerecommendations.However,GDGmembersdiscussedthechallengesassociatedwithobtainingcompellingevidencefromarandomizedcontrolledtrialonbehaviouralinterventions.Furthermore,withtheavailabilityofaSARS-CoV-2inoculation,furtherresearchwillbeneededtoreinforcetheimpactofvaccinationonmaskutilizationincommunitysettings.

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Justification

GDGmemberswereaskedtoevaluatethestrengthoftheproposedrecommendation(strongrecommendationversusconditionalrecommendation).Basedontheavailableevidence,theGRADEprocessandtheEvidencetoDecisionframework,theIPCGDGagreedonastrongrecommendation.TheopinionoftheGDGwassolidifiedviaanonlinesurvey,inwhich82.1%(23/28)ofGDGmembersvotedforastrongrecommendationand17.9%(5/28)votedforaconditionalrecommendation.

New

Goodpracticestatement

InsettingswherethereiscommunityorclustertransmissionofSARS-CoV-2,policiesshouldbedeveloped,strengthenedandimplementedtoencourageappropriateadherencetoacomprehensivepackageofpreventivemeasurestoreducetransmission(ventilation,physicaldistance,handhygiene,andrespiratoryetiquette)includinginparticular,maskadherencebythegeneralpublic.

Updated22December2021.

Justification

GDGmemberswereinitiallyaskedifWHOshoulddevelopastatementontheimportanceofmask-wearingand/orinterventionstoimproveadherencetomask-wearingguidance;however,manymembersthoughtitwasessentialtoconsiderthe“bundle”ofpublichealthsocialmeasuresthatpertaintothegeneralpublic.Theabovegoodpracticestatementwasdeterminedbyanonlinevote,where27GDGmembersresponded,with55.6%(15)votingforthestatementasmentionedabove,whiletheremaining44.4%(12)votedforslightlydifferentwordingforthegoodpracticestatement.

InalltransmissionscenariosofSARS-CoV-2

InfoBox

Updated

Implementationconsideration

Inareaswithknownorsuspectedsporadictransmission,ornodocumentedtransmission,WHOadvisethatdecision-makersshouldapplyarisk-basedapproachfocusingonthefollowingcriteriawhenconsideringtheuseofmasksforthegeneralpublic:

•purposeofmaskuse;

•riskofexposuretoSARS-CoV-2;

•vulnerabilityofthemaskwearer/population;

•settinginwhichthepopulationlives;

•feasibility;

•typeofmask;

•vaccinationcoverage;and

•circulatingvariantsofconcern.

Updated22December2021.

Justification

GDGmembersnotedtheimportanceofincludingvaccinationcoverageandcirculatingvariantsofconcerntotheimplementation

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considerationsgiventheavailabilityofvaccinationandthecurrentlandscapeofSARS-CoV-2transmission.

Inanytransmissionscenario,personswithanysymptomssuggestiveofCOVID-19shouldwearamedicalmaskandadditionally:

•self-isolateandseekmedicaladviceassoonastheystarttofeelunwellwithpotentialsymptomsofCOVID-19(evenifsymptomsaremild);

•followinstructionsonhowtoputon,takeoffanddisposeofmedicalmasksandwashhandsthoroughly[39];

•followalladditionalmeasures,inparticular,respiratoryhygiene,frequenthandwashingandmaintainingaphysicaldistanceofatleast1metrefromotherpersons[75].

•IfamedicalmaskisnotavailableforindividualswithsuspectedorconfirmedCOVID-19,afabricmaskwithfit,filtrationandbreathabilityassessedtomeetWHO'sessentialparametersfornon-medicalmasksshouldbewornbypatientsasasourcecontrolmeasure,pendingaccesstoamedicalmask.Theuseofanon-medicalmaskcanminimizetheprojectionofrespiratoryparticlesfromtheuser[40][41]

AsymptomaticpersonswhotestpositiveforSARS-CoV-2shouldwearamedicalmaskwhenwithothersforaperiodof10daysaftertestingpositive.

Extractedfromtheguidancetitled“MaskuseinthecontextofCOVID-19”,published1December2020.

EvidenceToDecision

CertaintyoftheEvidence

Evidenceontheprotectiveeffectofmaskuseincommunitysettings

Atpresent,thereisonlylimitedandinconsistentscientificevidencetosupporttheeffectivenessofmaskinghealthypeopleinthecommunitytopreventinfectionwithrespiratoryviruses,includingSARS-CoV-2[6].Alargerandomizedcommunity-basedtrialinwhich4862healthyparticipantsweredividedintoagroupwearingmedical/surgicalmasksandacontrolgroupfoundnodifferenceininfectionwithSARS-CoV-2[42].Arecentsystematicreviewfoundninetrials(ofwhicheightwerecluster-randomizedcontrolledtrialsinwhichclustersofpeople,versusindividuals,wererandomized)comparingmedical/surgicalmasksversusnomaskstopreventthespreadofviralrespiratoryillness.Twotrialsinvolvedhealthcareworkersandsevenhadcommunity-basedparticipants.ThereviewconcludedthatwearingamaskmaymakelittleornodifferencetothepreventionofILI(RR:0.99;95%CI:0.82–1.18)orlaboratory-confirmedinfluenza(LCI)(RR:0.91;95%CI:0.66–1.26)[11];thecertaintyoftheevidencewaslowforILI,moderateforLCI.

Bycontrast,asmallretrospectivecohortstudyfromBeijingfoundthatmaskusebyentirefamiliesbeforethefirstfamilymemberdevelopedCOVID-19symptomswas79%effectiveinreducingtransmission(oddsratio(OR):0.21;CI0.06-0.79)[43].Acase-controlstudyfromThailandfoundthatwearingamedicalornon-medicalmaskallthetimeduringcontactwithaCOVID-19patientwasassociatedwitha77%lowerriskofinfection(adjustedoddsratio(aOR)0.23;95%CI0.09–0.60)[44].SeveralsmallobservationalstudieswithepidemiologicaldatahavereportedanassociationbetweenmaskusebyaninfectedpersonandthepreventionofonwardstransmissionofSARS-CoV-2infectioninpublicsettings[2][45][46][47].

Anumberofstudies,somepeer-reviewedbutmostpublishedaspre-prints,reportedadeclineinthenumberofCOVID-19casesassociatedwithfacemaskusebythepublic,usingcountry-orregion-level

data.[48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69].Onestudyreportedanassociationbetweencommunitymask-wearingpolicyadoptionandincreasedmovement(lesstimeathome,increasedvisitstocommercial

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locations)[23].Thesestudiesdifferedinsetting,datasourcesandstatisticalmethods,andhaveimportantlimitationstoconsider[70],notablythelackofinformationaboutactualexposureriskamongindividuals,adherencetomask-wearingandtheenforcementofotherpreventivemeasures[71][72].

Studiesofinfluenza,ILIandhumancor