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The most recent guide from the World Health Organization (WHO) on the use of masks, published on Tuesday, in the context of the covid-19 pandemic, advises an (even) broader use of masks for everyone and in everywhere. , but with special attention to health units.
Maintaining that the update of these standards is the result of new scientific evidence, the experts point out that in “areas of confirmed or suspected community transmission of covid-19”, all people should wear a mask, indoors or outdoors, as long as they do not it is possible to maintain a spacing of at least one meter.
Indoors, the one meter distance rule does not apply when receiving visitors and in these cases everyone must wear a (non-surgical) mask.
Inside the house
“In an enclosed space, unless ventilation has been assessed as adequate, WHO advises the general public to wear a non-medical mask, regardless of whether it is possible to maintain a physical distance of at least one meter,” the document says. . This is, the experts point out, the fourth update of the guide on the use of masks, which this time includes a section of advice especially aimed at decision-makers of public health measures.
The WHO also takes the opportunity to advise against the use of masks during “intense physical activity”, does not support the use of masks with valves and reaffirms that the protection of the visors is very limited. The document also includes recommendations on the type of tissue to use in the manufacture of non-surgical masks.
The document has 22 pages with several paragraphs. However, the part that will have a larger goal is to wear a mask in the community. “Decision makers should apply a risk-based approach when considering the use of masks for the general public,” the guide reads, adding that “in areas known or suspected of community or group transmission SARS- Cov-2 “: WHO advises the general public to wear a (non-surgical) mask indoors (eg shops, shared workplaces, schools) or outdoors, where it is not possible to maintain a physical distance of at least minus one meter.
Indoors, when receiving visitors and unless ventilation has been assessed as adequate, WHO advises the use of a non-medical mask.
In health units
In this new recommendation, the WHO is especially strict in recommending the use of masks in health facilities located in regions where there is community transmission or confirmed outbreaks. This is at least “the opinion of the majority of experts (79%)” who are part of the WHO expert panel. Thus, despite admitting that this is not a unanimous position, the WHO maintains that “all health professionals, including community health professionals and caregivers, should always wear a medical mask, for any activity ( patient care) with covid-19 or others) and in any common area (for example, cafeteria, staff rooms) ”.
When it comes to other people (visitors, outpatients or service providers), the use of a mask (medical or non-medical) is also always recommended and only hospitalized patients are exempt from wearing a mask (medical or not) -medical), but only if it is possible to maintain a physical distance of at least one meter, for example, which does not include situations in which they are examined or visited at the head of the bed or when they are out of their care area (for example, when being transported). “The masks should be changed when they get dirty, wet or damaged, or if the health / caregiver removes the mask (for example, to eat or drink),” they warn.
Special for children
Specifically in children, the WHO reaffirms that those under the age of five should not wear masks and that for those between the ages of six and 11 “a risk-based approach should be applied to the decision to wear a mask; Factors to consider in the risk-based approach include the intensity of SARS-Cov-2 transmission, the child’s ability to comply with the appropriate use of masks and the availability of adequate adult supervision, the social and cultural environment. local and specific environments. such as homes with older relatives or schools ”. The use of masks in children and adolescents from 12 years of age should follow the same principles as for adults.
Fabrics for use in masks
Regarding the material that will be used for the manufacture of non-medical masks, WHO experts point out that the guarantee of protection is assured when they have three layers of fabric. The manufacture of these masks should be done with fabrics, such as cotton or cotton blends (in the inner layer), polyesters (in the outer layer) and nylon (in the middle layer) – which are breathable and guarantee adequate filtration performance when layered.
“Homemade fabric masks with a three-layer structure (depending on the fabric used) are recommended, each layer has a function: 1) an inner layer of a hydrophilic material; 2) an outer layer made of hydrophobic material; 3) a hydrophobic intermediate layer that has been shown to improve filtration or retain droplets, “say the experts, adding that” exhalation valves are not recommended because they bypass the filtering function of the tissue mask, rendering it unusable for control from the source. ”.
Other measures
The WHO standard deals with the use of masks, but here it is reaffirmed, once again, that this is only one of the measures of the “protection package” that all citizens must adopt. Thus, on the one hand, the importance of this resource is emphasized – remembering that proper use must be ensured that does not compromise its effectiveness – but it is also emphasized that the use of this medium alone is “insufficient to provide an adequate level of protection to an uninfected individual or prevent further transmission from an infected individual (source control) ”.
“Hand hygiene, physical distance of at least one meter, respiratory etiquette, adequate ventilation in indoor environments, testing, contact monitoring, quarantine, isolation and other prevention and control measures of infections are essential to prevent human-to-human transmission of SARS-Cov-2, whether or not masks are used.
Virus transmission
WHO experts also refer to a number of scientific study results (including publications and pre-publications) to support this advice. “The transmissibility of the virus depends on the amount of viable virus to be eliminated and expelled by a person, the type of contact that he has with others, the scenario and the measures in force. The virus can be spread through the mouth or nose of an infected person in small liquid particles when the person coughs, sneezes, sings, breathes a lot or talks, “they recall, adding that there is still little evidence on the transmission of the virus through objects. or contaminated materials.
“Outside of medical facilities, in addition to droplet and surface transmission, aerosol transmission can occur in specific settings and circumstances, particularly in crowded and poorly ventilated spaces where infected people spend long periods of time with other people. . Studies have suggested that these may include restaurants, choirs, fitness, discos, offices and places of worship, “warns the WHO.
However, despite the time that has elapsed and the thousands of studies that have already been carried out on this virus, the WHO emphasizes that “high-quality research is still needed to fill the knowledge gaps related to the modes of transmission, doses infectious diseases and definitions where transmission can be amplified ”. “Currently, studies are being carried out to better understand the conditions in which aerosol transmission or over-diffusion events can occur,” the experts acknowledge, adding that current evidence suggests that “people infected with SARS-Cov-2 can transmit the virus, whether they have symptoms or not ”, but that“ data from virus spread studies suggest that infected people have higher viral loads just before or around the time they develop symptoms and during the first five to seven days of illness”.
Differences between symptomatic and asymptomatic
Scientists will also have shown that, among patients with mild symptoms, the duration of the spread of the infectious virus is eight days from the onset of symptoms and longer for critically ill patients. “The period of infectivity is shorter than the duration of the detectable RNA spread, which can last many weeks,” he explains.
Regarding the incubation period (the time that elapses between exposure to the virus and the appearance of symptoms), it is maintained that it is on average five to six days, but it can reach 14 days. The WHO standard further stresses that “presymptomatic transmission (from infected people who release viruses, but have not yet developed symptoms”) and that asymptomatic transmission (people infected with SARS-Cov-2 who never develop symptoms) can occur .
“A systematic review of 79 studies revealed that 20% (17-25%) of people remained asymptomatic during the course of infection. Another systematic review, which included 13 studies considered to be at low risk of bias, estimated that 17% of the cases remained asymptomatic (14-20%) ”, the experts point out, insisting that“ the viable virus was isolated from samples of pre symptomatic and asymptomatic, suggesting that people who do not have symptoms can transmit the virus to others, ”although asymptomatic people are less likely to transmit the virus, according to other published studies. “A meta-analysis estimated that there is a 42% lower relative risk of asymptomatic transmission compared to symptomatic transmission.”
Studies on the effectiveness of the mask
Regarding the work that specifically analyzed the effectiveness of wearing a mask as a protective measure, the WHO admits that currently “there is only limited and inconsistent scientific evidence that supports the effectiveness of the use of a mask by healthy people in the community to prevent infection with respiratory viruses, including SARS-Cov-2 ”.
In the document, the WHO presents some examples of studies that concluded that the mask may have a low protective effectiveness, but also other studies that support the relationship between the use of a mask and the reduction in the number of infections. But, “despite limited evidence of the protective efficacy of mask use in community settings”, WHO concludes that mask use is recommended in a variety of settings (indoor and outdoor areas) where there is confirmed or suspected transmission in the community or an outbreak of the new coronavirus.
