Coronavirus, incubation period and planes: good, bad and no news

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Coronavirus, incubation period and planes: good, bad and no news
Coronavirus, incubation period and planes: good, bad and no news
Anonim

The Chinese authorities said that the coronavirus was allegedly spread by sick people during the incubation period before they showed symptoms. However, as shown by the reaction of scientists, there is no basis for such a statement. This is definitely good news. Perhaps it follows that the predicted billions of cases will not be. But there is worse news. The virus can probably be spread by airplanes: the intervals between the exit of old and the introduction of new passengers are too small, and the coronavirus capsids are able to survive them. Let's try to figure out what this means for the prospects of the ongoing epidemic.

If the coronavirus can spread to patients during the incubation period, then no reliable evidence of this has yet been found / © Getty Images

Over the past weeks, the coronavirus has shown itself to be more dangerous than the SARS epidemic of 2002-2003, of which it is the closest relative. To date, 40 627 people have been infected with it, 910 have already died. The most obvious reason for its danger is its great ability to spread compared to SARS.

This seems odd because the incubation period for the 2002-2003 virus is about the same length, four to six days (and one to 14 days for abnormal cases). According to some reports, the median (typical) incubation period can be as low as three days.

A possible reason for the greater "success" of the epidemic, oddly enough, is that fewer people die from it than from the "atypical". If for 11 patients with the 2002-2003 virus, there was one death, then for the new coronavirus in 2019, one out of 44 patients dies. The higher the death rate from the virus, the more difficult it is for it to spread, especially under quarantine conditions.

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A person who feels bad does not go to work or to the store, he sooner ends up in the hospital, where measures are taken to isolate him from society. As a result, such seemingly "mild" diseases become more deadly than SARS with its high mortality rate.

A typical example here is the well-known flu. People with their first symptoms often muffle them and try to work or go out (sometimes they think they are showing symptoms of a cold, not the flu). The flu does not seem serious to anyone, so every year it covers from tens to hundreds of millions, and its complications kill hundreds of thousands.

The 2019-nCoV coronavirus is not as "harmless" as the flu, therefore it is less contagious, and therefore the number of its victims is likely to be much less than that of the flu (recall, at least 250 thousand per year).Nevertheless, it is worth taking a closer look at how exactly it spreads around the planet.

Incubator for contagion: fear has big eyes

Some time ago, a Chinese medical official said that the virus is transmitted during the incubation period - when the patient has not yet shown symptoms of the disease. He does not have a fever, he does not cough - and doctors at the airport do not see him, examining the faces of passengers arriving from other countries in the infrared range.

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In theory, such a feature of the virus is very dangerous. The incubation period for infection from humans in 2019-nCoV is an average of five days, that is, everyone who travels by plane from China, in theory, can be infected with it, but not yet show symptoms. Therefore, the statement was extremely alarming.

True, the Chinese authorities have not provided any clear evidence that this is happening. But on January 30, The New England Journal of Medicine published an article that in Germany four people became infected from one Chinese woman who flew in from Wuhan, sick, but still without symptoms. Therefore, doctors at the airport could not cut her off, so that she was able to launch the coronavirus epidemic in Germany (so far extremely limited).

The head of the US National Institute of Allergies and Infectious Diseases, Anthony Fauci, then bluntly told reporters: “After this work, there is no doubt that asymptomatic transmission actually occurs. This work has put an end to this issue."

"There is no doubt about it"?

However, it was not for nothing that we wrote: "Such a trait in a virus is, in theory, very dangerous." In theory, it's the biological basis of viral infection. In order to infect another person, the coronavirus must be contained in the exhaled air, in droplets of moisture. But the virus can get into the exhaled drops of moisture only if it has already begun to reproduce in the human body in noticeable quantities.

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A logical contradiction arises here. A person gets sick from a new virus because in his lungs (and in a number of other tissues, but with less intensity) the virus multiplies, simultaneously destroying the cells, which he forces to continuously reproduce their copies. The virus itself cannot multiply - for this it needs to use the cells of the host's organism. The question arises: where, then, in the exhalation of a person without symptoms of the disease, capsids of viruses, carried by air to another person, can appear?

Usually, the answer to this question is this: at the early stage of the virus multiplication, human cells can already create copies of it, but not yet have time to die from this work or from the retaliatory strike of the immune system that reacts to such "printing" of copies of the virus in our cells. And then the person will not have symptoms yet, but will already be moderately infectious.

The concept "can be dangerous and the patient without symptoms" was born during the research of epidemics of common flu. A third of the people who are infected with his virus - the healthiest and strongest - do not feel at all that they are sick. They have no noticeable fever or other symptoms.

For a long time, doctors thought that such people ensure the spread of the influenza virus by secreting it in small quantities.Not in those who are actively ill, but the time spent by asymptomatic, "healthy" peddlers in public places is much longer than that of patients with fever and lying at home. People with coronavirus, in theory, could also begin to secrete viral capsids with droplets of saliva or sputum - as "asymptomatic" affected by the flu.

However, from a scientific point of view, such an idea still remained unclear. Well, there is a theoretical possibility of a moderate spread of the virus by an outwardly healthy person. But does it exist in practice, did anyone manage to fix it? In 2008, a group of researchers asked this question about influenza, and then it turned out that the whole idea of ​​asymptomatic transmission has always been pure theory. As they noted in their scientific work:

"We found that there is little, if any, evidence of transmission of influenza from a person without symptoms or from someone who has not yet shown symptoms (during the incubation period. - Ed.)."

They note that it is almost impossible to find convincing data on infection from a person in whom the flu has not yet produced vivid symptoms in the scientific literature. Yes, the day before the symptoms, the capsids of viruses can be found in swabs from the upper respiratory tract of infected people. However, their concentration there is quite small. And all experiments show that a statistically significant probability of infection begins to come from a patient only when he already has pronounced flu symptoms.

All this raises serious doubts. Even if we cannot find convincing evidence of transfer in the incubation period even for mass flu, why can they suddenly appear in the coronavirus, which, as you know, lived on bats until 2019 and should be less adapted for transfer from person to person?

Researchers at the Robert Koch Institute, a key German institution for the study of infectious diseases, were overcome with the same doubts following an article in The New England Journal of Medicine. They picked up and re-spoke on the phone with a Chinese woman who brought the disease to Germany.

It turned out that the lady actually had pronounced symptoms before she began to spread the disease across Germany. Her muscles ached, she had an incomprehensible fatigue, and she, without thinking twice, took paracetamol. The temperature dropped slightly and looked healthy in front of the doctors. An article in The New England Journal of Medicine was based on conversations with her German victims, which, of course, is not very deliberate.

Here, of course, one can be indignant at the behavior of a Chinese woman from Wuhan, who went to meet people instead of going to a doctor - at that moment the epidemic was already promoted in the media. But we will not do that. The lack of intelligence of certain representatives of our species is an objectively irreparable phenomenon, and it is useless to be indignant about this. The authors of the work in The New England Journal of Medicine explained their mistake by the fact that they were in a hurry - an epidemic after all. It turns out that it is also difficult to blame them for something.

Many models of the spread of the epidemic built to date in one form or another took into account the possibility of transmission from persons during the incubation period - vectors of the disease invisible to the medical authorities. This means that all of them, strictly speaking, will not work as predicted. For all of them, the number of victims may therefore be less than previously thought. It's a good news.

Airplanes and the coronavirus: this is not AliExpress for you

But there is also bad news: apparently, the coronavirus can be carried to some extent by airplanes.

We emphasize: today there is no experimental confirmation of this, because it is immoral to experiment with such a virus on living people, and it is difficult to find out from observations. However, scientists have a lot of material of observations of the spread of common flu in airplanes. It follows from it that on board passengers from the row where the patient with the flu sits have a noticeable chance of infection.

At the same time, the safest places are by the window. But even there, the likelihood of infection is quite high. The air in airliners is rather dry, which contributes to the increased vulnerability of the body to the virus. It is believed that in the annual flu season (in the United States, for example, ten thousand people have already died from it), it is the flights of sick people in airplanes that are one of the sources of infection.

According to a 1982 American study, the influenza virus can remain infectious on plastic or metal surfaces for up to 48 hours. Work in 2008 revealed that the virus remains infectious for up to 72 hours on banknotes. Porous surfaces (fabric, wood) are much more dangerous for the virus: the flu on them loses its ability to infect a person after four hours.

The coronavirus is different from the flu virus, but related coronaviruses often cause colds. Studies on them have shown that they cease to be infectious after 24 hours on a foreign surface. On human skin, the time they retain their infectiousness is even less - 20 minutes, but here it is not only the surface itself, but the symbiont microbes on it, which create an unfavorable environment for viruses.

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The problem is that smooth plastic surfaces are common on a typical aircraft, from entertainment devices to carry-on shelves and seat armrests. And the average time a liner spends on the ground in our time from 25 minutes (on short lines), up to three or four hours for the largest Boeing and Airbus. This means that, in theory, it is quite possible to catch the coronavirus if the plane on which you are flying was carrying a Chinese with a coronavirus who was sitting in the same seat as you.

Naturally, no one can thoroughly wash and disinfect the board in 25 minutes or even three hours. Surface cleaning does not negate the risk of virus transmission. Thorough cleaning varies from company to company in frequency, but on average occurs once every 500 flight hours and requires the liner to remain on the ground overnight. Such a procedure cannot be repeated often, otherwise it will ruin any airline: while the plane is on the ground, it does not bring it money.

It is impossible to say that nothing can be done in the second case. Many airlines have interrupted communications with China. However, it would be very rash to arrange this on a global scale: the world economy is built on close ties, and in fact, it is difficult to cut off contacts with the largest factory in the world.

What can we do ourselves without relying on the goodwill of airlines and authorities? If you have high attentiveness and self-control, avoid touching your face with your hands in the cabin of the airliner. The virus capsid from the surface of your face will not enter the respiratory tract by itself.He needs an intermediary, that is, hands.

Theoretically, you can wipe the surface of the entertainment screen and armrests, but it's far from the fact that you can remove the capsids from them. It will be a little easier to throw a blanket that has just been taken out of the packaging on the chair and try not to touch the objects around you once again.

It is also important to remember something else: according to the latest statements by Chinese doctors, the median age of patients in China is 47 years. This means that half of them are younger and half are older than 47, while the average age of China's population is almost ten less. That is, the greatest likelihood of getting sick is in persons aged 45 and older. If you belong to this group, you may need to take tougher precautions.

By the way, according to the latest data, although the average period of the incubation period of a new coronavirus is indeed several days, in some exceptional cases it can be equal to 24 days. Only after this period has passed since your last flight can you be quite sure that you have not become a carrier.

Let's summarize. Today it is clear that the 2019-nCoV coronavirus epidemic has become the largest event of its kind in the 21st century. At the same time, it still falls short in terms of the degree of danger either to the modern flu or to its outbreaks from the 20th century (the Hong Kong flu of 1968 claimed a million lives).

A new disease should be treated accordingly. About her, one should neither panic, talking about the alleged transfer to the incubation period, nor indulge in complacency, hoping that it will. The main thing is to maintain a reasonable balance between these two equally irrational states.

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