Masks inside out

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

Alexander Berezin, Naked Science

Moscow (and the castle, even the farthest – VM) is covered by a "shortage" of medical masks: everyone is trying to protect themselves from Covid-19. However, is this 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 as it seems at first glance. Let's try to figure out why.

All these masked people (a snapshot from the time of the current epidemic) clearly cannot be sick with coronavirus at the same time. That is, they expect the masks to protect them. It's amazing how gullible and how easily the representatives of our species fall into error / ©Wikimedia Commons.

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

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

The reason why the mask protects others from the germs of the person on whom it is worn is obvious: it delays and destroys only large drops (more than five micrometers in diameter) well. It is they who are thrown out when breathing (as well as when sneezing and coughing) by a person. However, the largest droplets are most likely to settle in the air, and it is most likely to get infected without direct contact from small droplets, less than five micrometers. They can stay in the air at face level for hours. They are the main cause of airborne infection.

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 filter layers (paper or other), and also – an important note – if it is disposable, that is, after one operation it is never used again.

As it is easy to see, the mask was originally conceived not to protect its wearer, but to protect against its wearer. Many doctors and scientists perceive it this way today. Dr. Eli Perencevich from the University of Iowa in the USA recently repeated this point of view in an interview with Forbes:

"The average healthy person should not wear a mask. There is no evidence that wearing a mask by a healthy person will protect him. Such people wear masks incorrectly and can increase the risk of infection because they touch their faces with a mask more often than usual."

Perentsevich adds that theoretically respirators (standard N95 or FFP, which delay 95% of incoming microparticles) can help, but in fact ordinary people do not know how to use them properly, they are left loosely fitted to the face. In addition, before removing the respirator from the face, you need to wash your hands – as well as after you took it off. People rarely like to wash their hands so often, and without this with a respirator, their chances of getting sick will only grow. Therefore, it is difficult to talk about efficiency here. Such respirators give a false sense of security, which can do more harm than help.

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

In 2015, a thorough analysis of what was experimentally found out about the possibility of protecting a healthy person with a mask from infection from the outside was published. According to this review work, everything is noticeably more complicated than it seems to Perentsevich and many of his colleagues. Studies when it was not possible to detect a reduced frequency of infection in the wearers of masks in comparison with those who did not use them, there really were. Only here 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 of similar content. In Canada, a team of 446 nurses who worked at the hospital during the flu epidemic was divided into two groups, one of which wore medical masks, and the other wore N95 level respirators. In the first group, 23.6% got the flu, in the second – 22.9%. In other words, in practice, the supposedly ineffective masks coped in the same way as the supposedly effective respirators. Interestingly, it is normal for 23% of staff to get sick in hospitals during flu epidemics, even if no one uses any protective equipment. It turns out that masks and respirators are equally ineffective and no different from the usual walking with an open face? Not quite.

In China, a study was conducted on 1,922 medical personnel and found that N95-level respirators seem to help with nosocomial infections (mostly non-viral), but they practically cannot prevent influenza infection. This is quite logical. A typical nosocomial infection is caused by a bacterium that is simply much larger than the capsid of the virus that causes influenza or Covid-19. It is not surprising that respirators delay bacterial infections, but they cannot slow down viral ones.

Another study – on 1,669 medical workers, also in China – compared the effectiveness of respirators and masks in protecting the carrier from nosocomial infections. It turned out that it is impossible to distinguish the effectiveness of masks from N95 standard respirators: 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 are particularly protected from small viral particles in practice, while masks and respirators protect comparably from diseases caused by bacteria.

...But sometimes protects against it

Further, the same review of 2015 touches on the usefulness of wearing masks by the population for the purpose of not infecting others with the carrier. Here it is based on an experiment in Hong Kong during the flu epidemic, with a sample of 407 people. All of them received a confirmed diagnosis, and then the researchers tried to prevent them from infecting their pets. Some of them were forced to wear masks, another – and wear masks, and often and thoroughly wash their hands, the third was not forced to do anything (control group).

A person in the middle of a sneezing cycle. It is clearly visible that many drops from his respiratory tract fly out very large. Such can be dangerous only at an extremely short distance and it is from their spread that medical masks help patients. Alas, they do not prevent their carrier from getting infected from small droplets, which are easier to penetrate through masks and respirators / © Wikimedia Commons.

It turned out that masks by themselves do not reduce the risk of infection by the patient at home. Even in combination with hand washing, they did this only when masks and hand washing were prescribed to the sick in the first 36 hours after they had symptoms.

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

Why don't you sweep masks off the shelves

Doctors and scientists often note that the preventive mass purchase of masks puts hospitals in difficult conditions during the epidemic: there masks need to be changed most often, but there is no place to buy them anymore. Therefore, the hype in Moscow and other major cities of the world – all these "buy a mask now, it won't be later!" – is not just useless, but directly harmful.

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

But altruism of this kind sharply contradicts the fact that masks are needed more in the hospital, 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 buying them out of altruism.

Total: there are no rational reasons to buy masks, and there are no irrational ones 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, wrote directly on his Twitter account:

"Seriously, people, stop buying masks! <...> If those who protect your health end up without them, it will put not only them at risk, but all of us."

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

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