From a scientific point of view: do masks help against the virus?

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From a scientific point of view: do masks help against the virus?
From a scientific point of view: do masks help against the virus?
Anonim

Moscow is covered by a "shortage" of medical masks: everyone is trying to protect themselves from Covid-19. However, is it realistic from the point of view of what is already known to science? Both masks and respirators can contain the epidemic, but not at all in the way it seems at first glance. Let's try to figure out why.

All these masked people (a snapshot of the current epidemic) clearly cannot be simultaneously sick with coronavirus. That is, they expect the masks to protect them. It's amazing how gullible and easily misleading our species are / © Wikimedia Commons

Medical mask: and does not think to protect its wearer …

At the end of the 19th century, under the influence of Pasteur's ideas about the transfer of diseases by microbes spreading with droplets of water in the air, surgeons suddenly realized that they were still working, exhaling microbes on the open wounds of operated patients. A person in a hospital often has a weakened immune system, and during surgery, the skin is a good barrier against bacteria - at the site of the wound it does not protect us in any way. Therefore, it is relatively easy to introduce a bacterial infection into a wound in this way. The surgeon first donned the mask in 1896, and since then this laudable custom has taken root in the medical environment.

The reason why the mask protects those around from the microbes of the person we are wearing is obvious: it well retains and destroys only large droplets (more than five micrometers in diameter). It is them that a person throws out when breathing (as well as when sneezing and coughing). However, the largest droplets are most likely to settle in the air, and infection without direct contact is most likely from small droplets, less than five micrometers. Those can stay in the air at face level for hours. They are the main cause of airborne infection.

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The surgeon contacts the patient at a very short distance: even large drops, falling down from his face to the patient, can easily reach an open wound. For him, the mask makes sense, although it is effective only if it includes special filtering layers (paper or others), and also - an important note - if it is disposable, that is, after one operation it is never used again.

As you can easily see, the mask was originally conceived not to protect its wearer, but to protect it from its wearer. Many doctors and scientists perceive it this way today. Dr. Eli Perencevich of the University of Iowa in the US recently echoed this point in an interview with Forbes:

“The average healthy person should not wear a mask. There is no evidence that wearing a mask in a healthy person will protect them. Such people do not wear masks correctly and may increase the risk of infection because they touch their faces with the mask more often than usual.

Perentsevich adds that theoretically respirators (N95 or FFP standards, which trap 95% of incoming microparticles) can help, but in fact ordinary people do not know how to use them properly, leaving them loosely fitted to the face. In addition, you should wash your hands before removing the respirator from your face - just like after removing it. People rarely like to wash their hands so often, and without it, with a respirator, their chances of getting sick will only grow. Therefore, it is difficult to talk about efficiency here too. These respirators provide a false sense of security that can harm rather than help.

Indeed, hands carry viral infections very often, and an increase in the frequency of touching the face is an undesirable consequence of wearing medical masks. Nevertheless, Dr. Perentsevich is not entirely right.

In 2015, a detailed analysis was released of what it was possible to experimentally find out about the possibility of protecting a mask of a healthy person from infection from the outside. With regard to this survey work, everything is noticeably more complicated than it seems to Perentsevich and many of his colleagues.Studies, when it was not possible to reveal a reduced frequency of infection in wearers of masks in comparison with those who did not use them, really were. Only now they concerned a sample of 32 people, that is, they simply cannot serve as a criterion for the real effectiveness of wearing disposable masks.

There were other experiments with similar content. In Canada, a team of 446 nurses who worked at a hospital during the influenza epidemic were divided into two groups, one wearing medical masks and the other wearing N95 respirators. In the first group, 23.6% fell ill with the flu, in the second - 22.9%. In other words, in practice, the supposedly ineffective masks did the same job as the supposedly effective respirators. Interestingly, it is normal for hospitals to get sick during flu epidemics 23% of the staff, even if no one is using any protective equipment. It turns out that masks and respirators are equally ineffective and do not differ in any way from the usual walking with an open face? Not really.

In China, a study was conducted on 1,922 medical personnel and found that N95 respirators seem to help with nosocomial infections (mostly non-viral), but practically cannot prevent infection with influenza. This is logical enough. A typical hospital-acquired infection is caused by a bacterium that is simply much larger than the capsid of the virus that causes the flu or Covid-19. Unsurprisingly, respirators stop bacterial infections, but cannot stop viral infections.

Another study - on 1,669 medical workers, also in China - compared the effectiveness of respirators and masks in protecting the wearer from nosocomial infections. It turned out that it is impossible to distinguish the effectiveness of masks from respirators of the N95 standard: both reduce the likelihood of nosocomial infectious diseases in the same way.

The general conclusion here is simple: it seems that neither masks nor even respirators protect against small viral particles in practice, while masks and respirators protect against diseases caused by bacteria, both masks and respirators are comparable.

… But sometimes it protects from him

Further, the same review of 2015 touches upon the usefulness of wearing masks by the population already with the aim of not infecting others by the wearer. Here it is based on an experiment in Hong Kong during the flu epidemic, with a sample of 407 people. They all received a confirmed diagnosis, and then the researchers tried to stop them from infecting their families. Some of them were forced to wear masks, others - and wear masks, and often and thoroughly wash their hands, the third was not forced to do anything (control group).

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It turned out that masks by themselves do not reduce the risk of infection by patients with his own family. Even in combination with hand washing, they did so only when masks and hand washing were prescribed to those who fell ill in the first 36 hours after they developed symptoms.

And here the conclusion is simple: if you just got sick, you should wear a mask and wash your hands thoroughly - this way you can less infect others. True, you can't help yourself.

Why you shouldn't sweep masks off the shelves

Doctors and scientists often note that preventive mass buying of masks puts hospitals in difficult conditions during an epidemic: masks need to be changed there most often, but there is no place to buy them. Therefore, the excitement in Moscow and other large cities of the world - all these "buy a mask now, then there will be no!" - not only useless, but downright harmful.

Let's think for a minute: why do people buy a mask? Because they think that wearing it will protect themselves from infections. No, it will not save you, above we have shown why. There remains only one reasonable buying motive - altruism. If the coronavirus hits me, I will put on a mask immediately after the first symptoms appear and will infect my neighbors less while I walk to the garbage chute and buy bread.

But this kind of altruism sharply contradicts the fact that in the hospital you need more masks, and if you buy them for yourself in case of illness, then the medical staff will then have nowhere to take new ones. Therefore, let's be honest: they are not being bought out of altruism.

Total: there are no rational reasons to buy a mask, and there are no irrational reasons either. They do this because they do not know about the practical uselessness of masks and respirators in the fight against viral infections.

That is why the chief physician of the US Public Health Service, Jerome Adams, directly wrote on his Twitter account:

“Seriously people, stop buying masks! If those who protect your health are left without them in the end, it will put at risk not only them, but all of us.”

In our opinion, this is an extremely sensible idea and the more people follow it, the better.

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