Background
This document provides advice on the use of masks in
communities, during home care, and in health care settings in
areas that have reported cases of COVID-19. It is intended for
individuals in the community, public health and infection
prevention and control (IPC) professionals, health care
managers, health care workers (HCWs), and community
health workers. It will be revised as more data become
available.
Current information suggests that the two main routes of
transmission of the COVID-19 virus are respiratory droplets
and contact. Respiratory droplets are generated when an
infected person coughs or sneezes. Any person who is in close
contact (within 1 m) with someone who has respiratory
symptoms (coughing, sneezing) is at risk of being exposed to
potentially infective respiratory droplets. Droplets may also
land on surfaces where the virus could remain viable; thus,
the immediate environment of an infected individual can
serve as a source of transmission (contact transmission).
WHO has recently summarized reports of transmission of the
COVID-19 virus and provided a brief overview of current
evidence on transmission from symptomatic, presymptomatic, and asymptomatic a people infected with
COVID-19 (full details are provided in WHO COVID-19
Situation report 73).
Current evidence suggests that most disease is transmitted by
symptomatic laboratory confirmed cases. The incubation
period for COVID-19, which is the time between exposure to
the virus and symptom onset, is on average 5-6 days, but can
be as long as 14 days. During this period, also known as the
“pre-symptomatic” period, some infected persons can be
contagious and therefore transmit the virus to others.In a
small number of reports, pre-symptomatic transmission has
been documented through contact tracing efforts and
enhanced investigation of clusters of confirmed cases.3-8 This
is supported by data suggesting that some people can test
positive for COVID-19 from 1-3 days before they develop
symptoms.
Thus, it is possible that people infected with COVID-19 could
transmit the virus before symptoms develop. It is important
to recognize that pre-symptomatic transmission still requires
the virus to be spread via infectious droplets or through
a An asymptomatic laboratory-confirmed case is a person infected with
COVID-19 who does not develop symptoms. Asymptomatic transmission
refers to transmission of the virus from a person, who does not develop
touching contaminated surfaces. WHO regularly monitors all
emerging evidence about this critical topic and will provide
updates as more information becomes available.
In this document medical masks are defined as surgical or
procedure masks that are flat or pleated (some are shaped like
cups); they are affixed to the head with straps. They are tested
according to a set of standardized test methods (ASTM F2100,
EN 14683, or equivalent) that aim to balance high filtration,
adequate breathability and optionally, fluid penetration
resistance. This document does not focus on respirators; for
guidance on use of respirators see IPC guidance during health
care when COVID-19 infection is suspected.11
Wearing a medical mask is one of the prevention measures
that can limit the spread of certain respiratory viral diseases,
including COVID-19. However, the use of a mask alone is
insufficient to provide an adequate level of protection, and
other measures should also be adopted. Whether or not
masks are used, maximum compliance with hand hygiene and
other IPC measures is critical to prevent human-to-human
transmission of COVID-19. WHO has developed guidance on
IPC strategies for home care12 and health care settings11 for
use when COVID-19 is suspected.
Community settings
Studies of influenza, influenza-like illness, and human
coronaviruses provide evidence that the use of a medical
mask can prevent the spread of infectious droplets from an
infected person to someone else and potential contamination
of the environment by these droplets.There is limited
evidence that wearing a medical mask by healthy individuals
in the households or among contacts of a sick patient, or
among attendees of mass gatherings may be beneficial as a
preventive measure.However, there is currently no
evidence that wearing a mask (whether medical or other types)
by healthy persons in the wider community setting, including
universal community masking, can prevent them from
infection with respiratory viruses, including COVID-19.
Medical masks should be reserved for health care workers.
The use of medical masks in the community may create a
false sense of security, with neglect of other essential
measures, such as hand hygiene practices and physical
distancing, and may lead to touching the face under the masks
and under the eyes, result in unnecessary costs, and take
masks away from those in health care who need them most,
especially when masks are in short supply.
Persons with symptoms should:
• wear a medical mask, self-isolate, and seek medical
advice as soon as they start to feel unwell. Symptoms can
include fever, fatigue, cough, sore throat, and difficulty
breathing. It is important to note that early symptoms for
some people infected with COVID-19 may be very mild;
• follow instructions on how to put on, take off, and
dispose of medical masks;
• follow all additional preventive measures, in particular,
hand hygiene and maintaining physical distance from
other persons.
All persons should:
• avoid groups of people and enclosed, crowded spaces;
• maintain physical distance of at least 1 m from other
persons, in particular from those with respiratory
symptoms (e.g., coughing, sneezing);
• perform hand hygiene frequently, using an alcohol-based
hand rub if hands are not visibly dirty or soap and water
when hands are visibly dirty;
• cover their nose and mouth with a bent elbow or paper
tissue when coughing or sneezing, dispose of the tissue
immediately after use, and perform hand hygiene;
• refrain from touching their mouth, nose, and eyes.
In some countries masks are worn in accordance with local
customs or in accordance with advice by national authorities
in the context of COVID-19. In these situations, best practices
should be followed about how to wear, remove, and dispose
of them, and for hand hygiene after removal.
Advice to decision makers on the use of masks for healthy
people in community settings
As described above, the wide use of masks by healthy
people in the community setting is not supported by current
evidence and carries uncertainties and critical risks. WHO
offers the following advice to decision makers so they apply
a risk-based approach.
Decisions makers should consider the following:
- Purpose of mask use: the rationale and reason for mask
use should be clear– whether it is to be used for source
control (used by infected persons) or prevention of
COVID-19 (used by healthy persons) - Risk of exposure to the COVID-19 virus in the local
context:
The population: current epidemiology about how
widely the virus is circulating (e.g., clusters of
cases versus community transmission), as well as
local surveillance and testing capacity (e.g., contact
tracing and follow up, ability to carry out testing).
The individual: working in close contact with
public (e.g., community health worker, cashier) - Vulnerability of the person/population to develop
severe disease or be at higher risk of death, e.g. people
with comorbidities, such as cardiovascular disease or
diabetes mellitus, and older people - Setting in which the population lives in terms of
population density, the ability to carry out physical
distancing (e.g. on a crowded bus), and risk of rapid
spread (e.g. closed settings, slums, camps/camp-like
settings). - Feasibility: availability and costs of the mask, and
tolerability by individuals - Type of mask: medical mask versus nonmedical mask
(see below)
In addition to these factors, potential advantages of the use
of mask by healthy people in the community setting include
reducing potential exposure risk from infected person during
the “pre-symptomatic” period and stigmatization of
individuals wearing mask for source control.
However, the following potential risks should be carefully
taken into account in any decision-making process:
• self-contamination that can occur by touching and
reusing contaminated mask
• depending on type of mask used, potential breathing
difficulties
• false sense of security, leading to potentially less
adherence to other preventive measures such as physical
distancing and hand hygiene
• diversion of mask supplies and consequent shortage of
mask for health care workers
• diversion of resources from effective public health
measures, such as hand hygiene
Whatever approach is taken, it is important to develop a
strong communication strategy to explain to the population
the circumstances, criteria, and reasons for decisions. The
population should receive clear instructions on what masks
to wear, when and how (see mask management section), and
on the importance of continuing to strictly follow all other
IPC measures (e.g., hand hygiene, physical distancing, and
others).
Type of Mask
WHO stresses that it is critical that medical masks and
respirators be prioritized for health care workers.
The use of masks made of other materials (e.g., cotton
fabric), also known as nonmedical masks, in the community
setting has not been well evaluated. There is no current
evidence to make a recommendation for or against their use
in this setting.
WHO is collaborating with research and development
partners to better understand the effectiveness and efficiency
of nonmedical masks. WHO is also strongly encouraging
countries that issue recommendations for the use of masks in
healthy people in the community to conduct research on this
critical topic. WHO will update its guidance when new
evidence becomes available.
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