Ventilation NOT lockdowns! Where the corona risk is high in winter – and where not


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Why ventilation matters! Corona viruses are transmitted through aerosols. The risk is minimal outside, but quite high in poorly ventilated narrow spaces.

Most corona experts agree on one thing: An increasing increase in infections can be expected again in autumn and winter. This also affects other viruses that spread through the air, such as influenza. Even if the German health system has never reached its limits so far and intensive care units were overloaded only occasionally, Corona could cause problems again this winter. The lower the vaccination rate in a federal state, the higher the numbers are expected. That is why people need to focus on ventilation.

Vaccinated people should also be careful

The main factor here, which the RKI also regularly points out: In autumn and winter, our life moves indoors, and the risk of infection is much higher there than in summer, when we spend a lot of time outside.

Why ventilation instead of lockdowns is the best strategy

The experts emphasize that, despite positive developments in respiratory infections due to Corona, one should continue to be vigilant: ” This will also affect vaccinated people, not least because the virus is constantly changing. It is currently unclear to what extent SARS-CoV2 vaccinated people and still infected people can pass the virus on. A vaccination therefore primarily protects against a severe course and the infections are much milder, “said the scientists.

Renewed lockdown measures must be avoided in any case. They have little use, but generate high social and economic collateral damage. Instead, experts propose a prevention check for interiors that minimizes the risk of infection according to the latest research.

Why aerosols are so treacherous

Indoor spaces are the central point of infection. There is no relevant risk of infection in the outdoor air (<0.01% compared to indoor spaces). The cause is to be found in the vertical flow generated by humans through the warm exhaled air and body heat (up to 100m³ / h), which strongly dilutes the exhaled aerosols. Wind currents outside also dilute the concentration.”

Aerosols are tiny air components that are exhaled even when speaking. The longer an infectious person is in a room, the more the aerosol concentration increases. And it is still there when the person is has long since left the room. If someone then enters this room, they can become infected. That is the tricky thing: You can become infected without even having met the vector. That is how for example 71 people in China become infected in an elevator.

However, there is only a risk if the aerosols can collect in sufficient quantities in the room. The experts understand their division of the interior spaces according to the risk of infection into “very low risk” to “very high risk” as ” practical instructions for everyday life”.

The following points system gives an indication of the risks of infection

Experts working with virologist Hendrick Steeck show where the risk of infection is high indoors and where it is not. 1 point: very low risk; 2-6 points: low risk; 6-10 points: medium risk; 11-15 point: high risk; 15-19 points: very high risk. If no CO2 or aerosol concentration measurements are available, then 0 points should be entered in each case – Source: The air hygiene check: Safe rooms in a pandemic

The point check according to scientists: when is the risk high and when not?

In a point system (see the above table), the rooms can be divided into different “risk classes”. Depending on the risk factor, up to four points are awarded or deducted. If no CO2 or aerosol concentration measurements are available, then simply enter 0 points in the table. The following factors play a role:

  • Number of people who are currently in an unventilated room or who may have been there until recently – The higher the number of people, the greater the likelihood that there is an infected person in the room and the more people there are in the room, the more people can potentially become infected.
  • Duration in the room – If there is an infectious person in the room, the concentration of viruses in the room air increases over time and the longer uninfected people stay in the room, the more viruses they inhale.
  • Volume of space – The larger the room, the lower the concentration of viruses in the room.
  • Room height – Due to the vertical flow generated by humans, high rooms are particularly safe because the exhaled virus-containing aerosols move upwards. This means that in high rooms – such as supermarkets, gyms, etc. – the risk is many times lower than in a narrow pub.
  • Ventilation effectiveness – The amount of fresh air that is supplied to the room dilutes the aerosols. ” With window ventilation, this depends in particular on the temperature difference inside / outside and the wind movement. The greater the temperature difference, the greater the effect. However, the energy consumption increases as a result of the cooling.
  • Effectiveness of indoor air purification devices.
  • Durability and effectiveness of masks worn by people in the room – Protective shields are ineffective because they do not prevent the infectious aerosols from spreading in the room. The effectiveness of masks in everyday life is controversial, as the discussion about the sense and nonsense of FFP2 masks in Bavaria has shown . In any case, one thing is certain: only a mask that fits tightly can serve its purpose well in the case of aerosol transmission.
  • Breathing rate and breathing depth of the infected and non-infected people in the room – Increased ventilation occurs, for example, during physical work, sport and singing.

2G rule in the supermarket?


If you look at the point system, it becomes clear that a “2G rule” like the one currently in Hesse – retailers are allowed to deny entry to unvaccinated people – would only make sense from a scientific point of view in small shops with close customer contact. On the other hand, in a supermarket (better ventilation, high and large rooms, short dwell time) or large halls, the risk of infection is low.

The “worst case scenario” for infections are narrow, poorly ventilated pubs or discos with many people talking or singing loudly. As has already been shown in practice, there were corona outbreaks in such locations even at events where the 2G or 3G rule applied.

Danger inside, not outside: The Robert Koch Institute clearly names the places where people are infected with the coronavirus. 
In the open air, people have almost nothing to fear

Be careful in toilets, elevators, buses and trains


The results of the “air hygiene check” essentially coincide with the information provided by the RKI in an overview of the risk of infection. As measures to minimize risk, the experts around the virologist Streeck suggest:

  • Limiting the number of people in a room
  • Limitation of the time people spend in a room
  • Priority use of large and high rooms (e.g. many gyms, auditoriums – these usually do not need any additional special protective measures)
  • Increasing the fresh air supply
  • Use of effective room air purification devices

” Small rooms with little or no ventilation (small offices and lounges, elevators, toilets, vehicles, public transport, etc.) are particularly unfavorable. Here, a concentrated, infectious aerosol cloud can remain in the air for a long time (similar to cigarette smoke) and then infect people who enter the room (e.g. cleaning staff). Sometimes virus spreaders and infected people never met, “the scientists said. 

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