Researchers led by the director of the Aerosol Research Center at Bristol University have published Jonathan Reid studied, in which they tried to simulate how the SARS-CoV-2 virus behaves after it gets into the air from an infected person.
Their main finding is a rapid decline in the virus’s ability to infect cells. It should drop by up to 90% in the air after 20 minutes, with the fastest drop in the first five minutes.
The study has not yet been reviewed, according to the Guardian, it was the first simulation of its kind in the world.
The results of the diary re-emphasize the importance of short-distance transmission of covid-19 in direct contact with the infected person. At the same time, the importance of measures that can prevent this mode of transmission, such as respiratory protection and social distances.
“People focused mainly on poorly ventilated areas and airborne transmission a few meters across the room. I’m not saying this isn’t happening, but I think the biggest risk is close contact, “the Guardian quotes Reid’s interpretation of the results.
Terms: droplet vs. aerosol
When sneezing, coughing, breathing, but especially during any vocal expressions, a person produces droplets. They then fly through the air. And as soon as the water evaporates, they become aerosol particlesthat move freely. This process occurs much better in colder weather, when there is less humidity in the air.
So far, according to the Guardian, knowledge about how long the virus survives in the aerosol has come from studies that have worked by spraying the virus into closed containers. They rotated so that the aerosol could fly in them. Under such conditions, it was concluded that the virus could remain infectious in the aerosol for several hours. However, according to the authors of the new study, this did not provide an accurate picture of what happens when the virus in the room exhales infected.
Therefore, the team developed apparatus that allowed them to generate any number of small particles containing the virus. The scientists were then able to watch them fly between two electric rings, where they also measured temperature, humidity and UV radiation.
Reid says it’s “the first time anyone has been able to simulate what happens to an aerosol when you exhale.”
According to the study, the particles with the virus, after leaving the lungs, ie a relatively humid environment rich in carbon dioxide, will quickly lose moisture and carbon dioxide. According to scientists, dryness and higher pH (acidity), which is caused by carbon loss, reduce the virus’s ability to infect cells.
According to the study, the virus lost infectivity faster in a humid environment. No effect was observed on air temperature.
The researchers have so far managed to test three variants of coronavirus, and even in this case they have not noticed that there is any difference between them in the monitored parameters. Omikron, which is now the most widespread in the world, is not to be tested until “in the coming weeks”.
Exaggerated conclusions, experts oppose
The Guardian adds an important response from Stephen Griffin, a virologist at the University of Leeds, who stressed that ventilation is also important in defending against the disease. “Without ventilation, aerosols will quickly fill the interior and will replenish as long as the infected individual remains in them,” said the scientist, who did not participate in the study.
However, several experts have long been more critical of the dangers of spreading covid-19 by aerosol. According to them, the conclusions in the eyes of people may undermine the fact that covid-19 can spread by aerosol over longer distances, which has been repeatedly demonstrated in the past. In addition, the interpretation of the results is said to be exaggerated and the apparatus used for the experiment, according to critics, does not simulate reality so well.
“A note on a Guardian article about an experiment whose results suggest that short-range transmission dominates: The experiments are great, but not entirely realistic, and do not fit into what we see in real-world data.” wrote on twitter American chemist from the University of Colorado at Boulder Jose-Luis Jimenez. He pointed out that there were already known many cases of people becoming infected over long distances.
Cases of the covid-19 spread over long distances were summarized last year by the Lancet magazine article listing 10 arguments that the disease is transmitted through the air not only through droplets but also through aerosols.
According to the Lancet, for example, cases of so-called “super-proliferation events” from around the world, confirmed cases of disease transmission among people who inhabited neighboring rooms in quarantine hotels and never met directly testify to this can happen even at greater distances in unventilated areas.
The Lancet also points to the fact that, according to real-world data, transmission is significantly higher in indoor, unventilated areas, or to disease transmission in animals in separate cages connected only by air ducts.
Update: We have supplemented the article with critical reactions from experts outside the study authors.