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The most recent World Health Organization (WHO) guide on the use of masks, released on Tuesday, in the context of the covid-19 pandemic, recommends an (even) wider use of masks for everyone and everywhere, but with particular attention to health units.
Maintaining that the update of these standards comes from 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, inside or outside, every time it is not possible to maintain a spacing of at least one meter.
Inside, 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 public to wear a non-medical mask, regardless of whether a physical distance of at least one meter can be maintained,” reads the document. This is, the experts note, the fourth update of the guide on the use of masks, which this time includes a section of advice aimed especially at decision makers of public health measures.
WHO also takes the opportunity to advise against the use of a mask during “intense physical activity”, does not support the use of masks with valves and reiterates that the protection of visors is very limited. The document also includes recommendations on the type of tissue to be used in the manufacture of non-surgical masks.
The document has 22 pages with several paragraphs. However, the part that will have a broader focus is the use of 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 known or suspected areas of transmission of communities or groups SARS-Cov-2 “: WHO recommends that the general public should wear a (non-surgical) mask indoors (for example, shops, shared workplaces, schools) or outdoors, where a physical distance of at least one meter.
Inside, when receiving visitors and unless ventilation has been evaluated as adequate, WHO recommends the use of a non-medical mask.
In health units
In this new recommendation, WHO is particularly strict in recommending the use of a mask in health care 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 group. Therefore, despite admitting that this is not a unanimous position, WHO argues that “all health care professionals, including community health professionals and health care professionals, should always wear a medical mask, for any activity (patient care) with covid-19 or others) and in any common area (eg cafeteria, staff rooms) “.
When it comes to other people – visits, people on an outpatient visit or service providers – the use of a mask (medical or non-medical) is also always recommended and only hospitalized patients are exempted from wearing a mask (medical or minus) -medical), but only if a physical distance of at least one meter can be maintained, for example, which does not include situations where they are examined or visited at the head of the bed or when they are outside their care area (for example , during transport). “Masks need to be changed when they get dirty, wet or damaged, or if the healthcare professional / caregiver removes them (for example, to eat or drink),” they warn.
Special for children
In particular on children, WHO reiterates that children under five should not wear masks and that for those between six and 11 years of age “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 transmission of SARS-Cov-2, the child’s ability to use masks correctly, and the availability of adequate adult supervision, the social environment and local culture and specific environments, such as homes with elderly family members or schools “. The use of masks in children and adolescents aged 12 and over must follow the same principles as adults.
Fabrics to be used in masks
As for the material to be used for the manufacture of non-medical masks, WHO experts note that the guarantee of protection is ensured when they have three layers of fabric. The manufacture of these masks must be made with fabrics, such as, for example, cotton or cotton blends (in the inner layer), polyesters (in the outer layer) and nylon (in the middle layer) – which are breathable and ensure adequate filtration performance when layered.
“Homemade fabric masks with a three-layer structure (depending on the fabric used) are recommended, with each layer having a function: 1) an inner layer of a hydrophilic material; 2) an outer layer in hydrophobic material; 3) an intermediate hydrophobic layer that has been shown to improve filtration or retain droplets, “say the experts, adding that” exhalation valves are discouraged because they bypass the filtering function of the tissue mask, rendering it unusable for source control . “.
Other measures
The WHO standard concerns 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. Therefore, on the one hand, the importance of this resource is emphasized – remembering that adequate 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 a level adequate protection to a non-infected individual or to prevent further transmission from an infected individual (source control) ”.
“Hand hygiene, physical distance of at least one meter, respiratory label, adequate indoor ventilation, testing, contact monitoring, quarantine, isolation and other prevention and control measures infections are essential to prevent human-to-human transmission of SARS-Cov-2, regardless of whether or not masks are used. “
Transmission of the virus
WHO experts also refer to a range 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 that must be eliminated and expelled by a person, the type of contact they have with others, the scenario and the measures in place. The virus can spread from the mouth or nose of an infected person into 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 materials. contaminated.
“Outside of medical facilities, in addition to droplet and surface transmission, aerosol transmission can occur in specific environments and circumstances, particularly in crowded and inadequately 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 elapsed and the thousands of studies already carried out on this virus, WHO stresses that “high-quality research is still needed to fill the knowledge gaps related to modes of transmission, infectious dose and definitions where transmission it can be amplified ”. “Studies are currently underway to better understand the conditions under which aerosol transmission or super-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 individuals have a higher viral load just before or around the time they develop symptoms and during the first five – seven days of pathology “.
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 detectable RNA diffusion, which can last for many weeks,” he explains.
Regarding the incubation period (the time between exposure to the virus and the onset of symptoms), it is believed to be five to six days on average, but can reach 14 days. The WHO standard also points out that “presymptomatic transmission (from infected people shedding viruses but who 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 the infection. Another systematic review, which included 13 studies considered to be at low risk of bias, estimated that 17% of cases remained asymptomatic (14% -20%) “, underline the experts, insisting that” the viable virus is been isolated from samples of pre-symptomatic and asymptomatic, suggesting that people who have no symptoms may be able to pass 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 masks
Regarding work that specifically examined the effectiveness of wearing a mask as a protective measure, WHO admits that currently “there is only limited and inconsistent scientific evidence to support the effectiveness of wearing a mask by healthy people in the community to prevent infection with respiratory viruses, including SARS-Cov-2 ”.
In the paper, WHO presents some examples of studies that concluded that the mask may have low protective efficacy, 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 wearing masks in community settings”, WHO concludes that the use of masks is recommended in a variety of settings (indoor and outdoor areas) where there is confirmation or suspicion of transmission. in the community or outbreak of the new coronavirus.
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