As you return home late in the evening, you are confronted by a robber in a dark alley. The chances of protecting your dignity, money, or even your life depend heavily on whether you face one or four robbers.

It’s true that in some cases you can be capable of defending yourself even from four people. However, it could also the case that only one of those robbers could hurt you and steal your money. Nevertheless, the general rule is that the fewer the robbers, the higher the chance of protecting yourself.

Here are some more details.

In order for a person to get infected with the coronavirus, he or she has to get a certain amount of the virus in his/her respiratory airways or eye conjunctiva.

The key here is “a certain amount of the virus.” This is a very important point!!!

Here is what I mean. If you get one particle of the virus, you won’t develop the sickness; if you get ten particles, you won’t develop the sickness either; yet, you will get sick after being exposed to 100 particles of this virus.

In other words, there is a minimal number of virus particles necessary to make a person sick. This is known as an infectious dose.

The infection dose depends on many factors, such as the properties of the virus, mechanisms of spreading, and previous exposure (if you already had some exposure to this virus, the infection dose must be greater).

What do we know about the coronavirus COVID-19 so far? Not much, but here are the basics:

  • highly damaging (virulent) virus
  • spreads through respiratory droplets or by close contact or touch
  • no prior human exposure

Therefore, the infection dose is small. Although right now no one can state with certainty how many particles of the virus must be absorbed by the human body in order to cause illness, yet, it is not a large amount.

Now, the most important part.


The likelihood of infection and the severity of the illness directly depends on the amount of the virus that enters the human body. Thus, holding all else constant, the more particles entering the human body, the higher the probability of getting sick and developing conditions with higher severity.

Being exposed to one “infection dose” is not a terrible scenario as there are high chances of developing mild or even asymptomatic form of the illness.

However, exposure to ten infection doses could be life-threatening.

Now, let’s ask a specific question:

Under what conditions the number of the virus particles is at its pick in the surrounding air?

Let’s together create an ideal environment that will get us not merely sick but seek indeed. To achieve that, we should inhale a greater dose of the virus to increase our chances of ending up with severe illness:

  1. We need a person who sheds the virus in the surrounding area. It would be great if we can find not one but several people, and even better if those people experience shortness of breath, and they cough and sneeze.
  2. It is necessary that the emitted virus particles by the sick person accumulate in the air. Here is what is needed: a small room with no source of airing. It is also important to account for the humidity of the air because the virus particles must float in the air for as long as possible and not fall by the force of gravity; under a relative humidity of the air between 40-60%, the particles won’t float for long.
  3. Bonus. Virus droplets exhaled by an infected person do not travel very far (1-1,5 meters) and then quickly land onto a surface. However, the duration and the distance of the virus’ “flight” can be increased! In order to achieve that, the infected droplets need to be mixed with other gases or aerosols. For instance, we could have someone smoking (anything), performing inhalations, breathing oxygen, etc.

Given this information, we can easily name locations where it is most likely to be exposed to high infection doses, which can potentially be deadly:

  • The first place surely is an Intensive Care Unit (ICU) - several contagious people in addition to oxygen flow. If an ICU is small, has no adequate circulation of fresh air, and dry breathing air, it creates an ideal environment to be exposed to ten infection doses at once (this actually explains the massive infection and death rate of medical staff).
  • Any places with loads of people in proximity not keeping social distancing with poor circulation of fresh air- churches, barracks, jail cells, subway cars, etc.
  • Any closed space buildings where people gather for events (concerts, circus, conferences, etc).
  • Nursing homes for the elderly and disabled people are a special case. It’s a place where the most vulnerable group of people live together in a closed-up space, where even one dose could be deadly. Also, such people tend to feel cold, thus, there is no airing. In addition to that, they use breathing machines.

Now you can answer many questions yourself:

  • Why did this young and health nurse die?
  • Why there is a terrible situation in jails and nursing homes?
  • Why crowds are prohibited?
  • Why people who are not scared of airing, and households with a small number of family members (not three generation leaving together) tend to get sick less?
  • Why are the parks closed (that is strange)?


The coronavirus is not going away. It will leave us alone only when the majority of people get exposed to the virus and develop herd immunity. It won’t be possible to achieve it over the winter and the spring, yet, it will get easier over the summer because people will open their windows, central heating systems will be turned off, and air humidity will normalize. In addition to that, people will be breathing fresh air by getting out more, the temperature of doorknobs/handles and the amount of ultraviolet will increase. Lastly, we will finally learn how to wash our hand.

Nevertheless, in the fall, the chances of a second outbreak of the virus are very high. This means that those people who haven’t developed immunity this spring will develop it in the fall, next winter, or even next spring. So far there are no other alternatives.

With that being said, we shouldn’t put our best efforts toward complete lockdown while waiting for a saving vaccine (which we might not get on time). Contrary, we should create a lifestyle that will eliminate situations that provoke the development of severe illness.

If each of us inevitably must meet up with the coronavirus, let’s do it in small doses.

If in supermarkets with modern ventilation systems there are no crowds and people keep 2 meters distance, why not?

If a bus will have an open window vent and passengers keep social distancing, why not? (If you are bothered by the airflow from the window vent, you can go by foot; it is very safe).

This year, coffee shops, bars, and restaurants with outdoor seating will be trending more than ever.

All government officials (from the president to the community council) meet with their employees and organize press-conferences only outdoors. Likewise, church staff should meet with churchgoers outside, teachers should meet with their students outside… Basically, anything that can be done outside of a building should be done outside.

When entrepreneurs and customers discuss an opening of a company, store, beauty salon, restaurant, club, daycare, preschool, high school, etc., they should be concerned with the following:

  • How to provide, control, and measure the optimal parameters of temperature, air humidity, and ventilation
  • How many people will be there at once within a given square footage.

The main goal of the authorities and the experts in the health area (such as the National Institute of Hygiene of Hygiene, Division of Public Health, departments of epidemiology and hygiene at the medical schools) is to provide practical and easy-to-follow guidelines. The guidelines will have standards for appropriate density of people per square foot, directions for ventilation installation, measures and control of air humidity, list of appropriate disinfecting and cleaning supplies, and so on.

One more important role of the government authorities is to explain to the public (and themselves) that adequate air circulation, handwashing, and social distancing are much more effective than massive purchases of the mechanical ventilators.

P.S. It is better to avoid connections with criminals. Nevertheless, if you do meet them, do it in an ally with an airing.

(Благодарим за перевод статьи Евгения Олеговича Комаровского "Коронавирус: доза имеет значение, а место встречи можно изменить" на английский язык Ольгу Шаповал.)

автор Комаровский Е.О.
опубликовано 23/04/2020 18:17
обновлено 24/04/2020


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