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No lingering zone in Düsseldorf
Photo: Roland Weihrauch / dpa
The city of Düsseldorf's slogan - »Proximity meets freedom« - has a PR problem in the pandemic, and currently particularly: Fridays to Saturdays at certain times of the day in certain areas of the city there is a so-called no-stay ban.
Not everyone thinks that's good.
On the other hand, the state is currently facing a third corona wave that will primarily affect younger people.
Politicians want to show that they are taking action.
For example the prohibition to stay.
There are also strict rules for discussions elsewhere, such as in Hamburg.
There, for example, parents have to wear mouth and nose protection when they are out and about on the playground with their children; masks are also compulsory on populated areas, even for joggers, cyclists or walkers.
In Hamburg's Corona regulation there is a detailed list that includes streets and squares, sometimes down to the house number.
But what are the benefits of rules such as the prohibition to stay in the park and the requirement to wear a mask?
Experts find it difficult to quantify the exact impact of a particular measure on the course of the pandemic.
Basically, the following applies: In case of doubt, the risk of a corona infection is much higher indoors than in the fresh air.
Mobility researcher Kai Nagel from the TU Berlin can substantiate this with data; he models the pandemic in the capital on the basis of anonymized cell phone data.
Various parameters of its simulation can be adjusted, so, among other things, the respective anti-corona measures can be mapped - and also the different dangers indoors compared to outdoors.
"If you move activities from inside to outside, we expect a ten times lower risk of infection in our model," says Nagel.
That doesn't mean that outside rules are per se pointless.
Because of course there can also be dangerous aerosol clouds in the air when infected coronaviruses exhale.
When people talk to each other, these aerosols are, as it were, blown into the face of the person you are talking to.
While the viruses can collect in unventilated rooms, the exhaled air is quickly diluted and removed outdoors, as it is called by the Society for Aerosol Research (GAeF) in Cologne.
Stricter rules would be necessary - but which ones?
The former President of the International Society for Aerosols in Medicine, Gerhard Scheuch, does not consider a brief encounter with people in the fresh air to be problematic.
The amount of viruses that you might get off in passing is not enough for an infection, according to the advisor to the European Medicines Agency Ema.
"Jogging, running, hiking, going for a walk, I consider that to be absolutely harmless."
The GAeF also gives the all-clear in its position paper: "There are virtually no infections caused by aerosol particles outdoors." However, caution should be exercised in groups in which no minimum distances are observed and / or masks are not worn - for example during longer conversations .
That may be the background for decisions such as the no-stay permit.
Especially since it is also clear that the rules that have been so tolerably effective to contain the Sars-CoV-2 pathogen against the more easily transmitted virus variants are no longer sufficient.
From the point of view of fighting a pandemic, contact that is still just acceptable in terms of distance, duration and ventilation is no longer in doubt in times of mutants.
Stricter rules can make sense - the question is whether you should start doing this in the park or maybe in the offices.
So far, for the Robert Koch Institute (RKI), people who stand together with an infected person for longer than 15 minutes without any protection and less than 1.5 meters apart are considered to be contact persons with a "higher risk of infection".
However, it is not certain that the FFP2 masks reliably reduce the risk of infection in a constellation.
Moist exhaled air can reduce the effectiveness of the FFP2 masks if they are not changed and dried regularly.
In addition, if the material is moist, droplets from the outer surface of the FFP mask could end up in the environment through coughing or sneezing.
The fundamental problem with these measures, however, is different.
In any case, researcher Nagel says: "Because the risk of infection is lower in the open air, people should be encouraged to stay there - and not deliberately made unattractive."
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With material from dpa