Enlarge /. The French fashion student sews homemade face masks to stop the spread of COVID-19.
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The World Health Organization updated its guidelines on the use of masks during the COVID-19 pandemic on Friday and made various changes and additions. Above all, the agency now recommends that governments encourage healthy members of the public to wear masks as part of extensive prevention efforts in certain situations.
With the new guidelines, the agency is in line with many countries around the world that have already recommended masking the public, including the United States Centers for Disease Control and Prevention, which issued the recommendation in early April.
However, the WHO issued its updated guidelines with many reservations and some highly specific recommendations that were not given by the US CDC.
"I would like to say very clearly that the guidelines that we are publishing today are an update of what we have been saying for months: masks should only ever be used as part of a comprehensive strategy against COVID," said WHO Director General Tedros Adhanom Ghebreyesus (Dr. Tedros) said in a press conference on Friday.
"Masks alone won't protect you from COVID-19."
The technical guidelines, which will be released later on Friday, are equally cautious: "Currently, the widespread use of masks by healthy people in the community is not yet supported by high quality or direct scientific evidence, and there are potential advantages and disadvantages to them Consider."
who and when
However, the WHO decision to recommend masking to the public was influenced by concerns that the disease would spread to infected people who showed no symptoms (pre-symptomatic and asymptomatic transmission). The agency also considered "individual values and preferences" and the fact that physical distancing is difficult, if not impossible, in some contexts.
Most recently, WHO emphasized that its updated guidelines are based on new data and offer detailed technical advice on homemade mask construction.
"This is a new type of novel research that WHO commissioned that we didn't have a month ago," said Maria Van Kerkhove, WHO technical director for the COVID-19 response, at Friday's press conference.
In particular, the WHO now recommends that healthy citizens wear homemade or commercially available cloth masks in places where the new coronavirus is common and where physical distance (6 feet away, etc.) is not possible or difficult.
Enlarge /. Who should wear a mask and when?
And these recommended masks are not just any face covering. The agency examined the filtration and breathability of a variety of common fabrics and materials. The French Standardization Association (AFNOR Group) was found to have developed a technical standard for non-medical masks that included at least 70 percent solid particle or droplet filtration.
The WHO determined that breathability – the pressure difference between the masks while breathing, expressed in millibars (mbar) or pascals (Pa) – should be less than 49 Pa / cm2 for a medical mask. For non-medical masks, however, an acceptable pressure difference should be less than 100 Pa.
Finally, the WHO calculated the filter quality factor "Q", which is a function of filtration and breathability, with higher values indicating better overall efficiency. The absolute minimum for homemade fabric masks should be Q of 3, according to the WHO expert consensus.
Next, the analysis revolved around the mask assembly – the best materials and layering methods. Folding a single fabric in two layers can increase filtration two to five times. Wrinkles that form four layers increase the filtration up to seven times.
The WHO found that at least three layers are required for fabric masks. Depending on the fabric used, however, masks may need more. For example, folding cotton handkerchiefs in four layers, according to the WHO, still only led to a maximum filtration efficiency of 13 percent. In particular, the homemade masks recommended by the US CDC have only two or three layers of cotton.
Enlarge /. Analysis of possible mask materials.
Given the lower standards for even the best homemade masks, the WHO emphasized that these masks are for source code management only and not for personal protection. That is, they can help prevent the spread of the virus by the person wearing the mask, but they do not necessarily protect the wearer from infection. It is therefore important that the wearing of a mask is always accompanied by frequent hand washing and physical distancing.
Overall, the expert analysis landed on this mask design:
The ideal combination of materials for non-medical masks should include three layers as follows: 1) an innermost layer of a hydrophilic material (e.g. cotton or cotton blends); 2) an outermost layer of hydrophobic material (e.g. polypropylene, polyester or their mixtures) which can limit external contamination from penetration to the nose and mouth of the wearer; 3) a medium hydrophobic layer of synthetic fleece such as polypropylene or a cotton layer that can improve filtration or retain droplets.
Van Kerkhove noted in the press conference that “the evidence we have through this research is that with these three layers and in this combination, this substance (masks) can actually be a mechanistic barrier. If someone were infected with COVID-19, this could prevent these droplets from penetrating and infecting someone else. "
Enlarge /. Mask boxes and bans. The instructions did not contain any specific details for testing the recommended mask design or comparing it with others, such as: B. that recommended by the CDC. Ars has requested additional data from the WHO and will update this piece as it becomes available.
In addition to fabric masks for public use, the WHO is now also recommending that in areas where COVID-19 is spreading, all healthcare workers should always wear medical masks, even if they do not treat COVID-19 patients specifically.
In areas with COVID-19 spread, all people aged 60 years and over and people with an underlying health condition should wear a medical mask if physical distance is not possible.
Finally, the WHO gives advice on washing your mask and on putting it on and taking it off safely.
"Masks are not a substitute for physical distance, hand hygiene, and other public health measures," said Dr. Tedros. “Masks are only useful as part of a comprehensive approach to fighting COVID-19. The cornerstone of the response in each country must be to find, isolate, test and maintain each case, and to track and quarantine each contact. That is what we know works. This is every country's best defense against COVID-19. "