Epidemic: how far should you stay from a sick person? It’s above all a question… of culture

Almost four years after the start of the pandemic, barrier gestures are still firmly anchored in people's minds. Among them, social distancing, which invited us to stay one meter away from other people. In any case in France... Because elsewhere in the world, sometimes very different distances have been adopted. Would viruses travel more or less far depending on the country?

In a recent study published in Plos One by researchers from the Jacques Monod Institute, in Paris, and the University of Montpellier, compared distancing practices in more than 190 countries during the first wave (2020). They found that 45% of them advocated a distance of one meter, while 49% opted for 1.5 to 2 meters. (The remaining 6% did not specify an exact value). But no country has increased these minimum distances, even when several studies have shown that SARS-Cov-2 could contaminate an individual located more than 2 meters from an infected person. How were these distances chosen, and did this have an influence on the course of the epidemic?

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We know that infectious germs from respiratory viruses, such as those of the flu, bronchiolitis and Covid, are transmitted via drops of saliva emitted when we speak, sneeze or cough. “When these droplets fall on the ground or surfaces, we sometimes have to touch them. Although this route of contamination is anecdotal, it was used by health agencies during the Covid pandemic to justify washing hands and surfaces,” underlines Antoine Flahault, professor of public health at the University of Geneva and director from the Institute of Global Health. These same spittle can encounter during their flight the entrance doors to our body (eyes, nostrils, mouth); they fall towards the ground within a radius of one meter, the WHO has therefore recommended this distance since the 1950s. But during the Covid-19 pandemic, contamination by aerosols, that is to say via microdroplets of saliva (less than one hundred microns), has established itself as the almost exclusive route of transmission of Covid-19. Lighter than sprays, these microdroplets go further. And each country has opted for very heterogeneous distancing recommendations: in Greece or the United Kingdom, it is 2 meters; in Senegal, 1 meter; in Switzerland 1.5 meters.

But what impact did this choice really have on the progression of the virus? The researchers found that countries that immediately recommended a distance of more than 1 meter from the first wave did not necessarily have less transmission of Covid-19. “Our statistical analyzes showed no correlation to confirm that the choice of a greater distance was associated with lower transmission,” confirms Virginie Courtier-Orgogozo, CNRS research director, who led this study. “The epidemic progression brings so many factors into play that it is utopian, even today, to talk about ideal distance,” says Jean-Michel Pawlotsky, virologist at CHU Henri-Mondor (Créteil). It depends on the quantity of infectious germs that a sick person produces, which varies depending on the phase of infection, but also on the size of the droplets emitted, the outside temperature, the degree of humidity, seasonality, etc.

Keeping your distance from a sick person is not absurd, because it limits the risk of contagion; but the effect would remain modest. “When a sick person leaves a poorly ventilated room, the cloud of droplets continues to float in the air for several minutes or hours,” emphasizes Professor Flahault. However, knowing that we inhale approximately 20 times per minute, if this cloud is contaminated with infectious germs, a non-sick person inhales the virus 20 times per minute spent in the unventilated room. By staying there for an hour, it’s as if we had been exposed to the virus 1,200 times.” Moving 1 or 2 meters away ultimately changes the risk very little.

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But scientific data was not the only parameter taken into account in defining the distances to be respected, the researchers noted. Legal, monetary system and cultural practices also had an influence. “Regardless of the pandemic, the closeness between two individuals varies greatly based on relationships, age and especially culture. This cultural signature seems to explain the choice of safety distances,” explains Professor Courtier-Orgogozo. The scientists found that in countries where people are physically closer in the family context, the recommended distances tended to be lower. This is particularly the case for Italy, which has recommended a distance of 1 meter.

An observation which is ultimately “absolutely not” surprising for Professor Pawlotsky. “On the contrary, it is reassuring to see that there is a much more global reflection that is compatible with everyone’s lifestyles.” “The authors rightly point out that providing a precise value to the citizenry makes it easier to understand the message, although the value itself is relatively arbitrary. Today we almost want to say that the further the better, but in the same way that we recommend 5 fruits and vegetables, 10,000 steps per day or 7 hours of sleep, it is easier to refer to a threshold », adds Antoine Flahault.