There is still insufficient evidence for the World Health Organization to prove that the new coronavirus is dispersed in the air. Although some scientists begin to disagree. Research continues
A growing number of studies suggest that the new coronavirus is able to remain on surfaces even for days and to disperse in the air for a few hours. The question, at this point, arises spontaneously: if the virus spreads in the air, what is the risk we run of being infected even if we breathe contaminated air ? According to the World Health Organization (WHO), the new coronavirus is mainly transmitted from person to person, through the droplets , droplets of saliva that are expelled when speaking, coughing and sneezing and which, being relatively heavy, fall on the eyes, nose, mouth and hands of those in the immediate vicinity. And that's why the WHO recommends keeping the safety distance (and using the masks only if you are suspected of being positive or if you are assisting a patient).
But some scientists disagree and claim that the new coronavirus can also be transmitted via aerosol , i.e. through particles with diameter less than 5 micrometers , therefore much more small and light of the droplets , which may remain suspended in air for long periods of time. And if it were really so, it is possible that virus particles could accumulate over time in closed environments or be transmitted at greater distances . In this view, therefore, some experts recommend a preventive use of the masks and to regularly ventilate the closed rooms. In response, the WHO pointed out in a report published last 27 March, that there is insufficient evidence to prove that the new coronavirus remains suspended in the air, except in hospital settings .
However, according to the scientists, the collection of unequivocal evidence of virus transmission via aerosol , it may take years. “In the thought of the scientists working on this, there is absolutely no doubt that the virus spreads in the air” , explains in the magazine Nature Lidia Morawska , researcher at Queensland University of Technology in Brisbane, Australia. And although coronavirus transmission occurs primarily at close range, adds Ben Cowling, an epidemiologist at the University of Hong Kong, the distinction between droplets and aerosol is useless. “The escaping particles can have a wide range of sizes. From very large to aerosols “, comments the expert.
The debate between skeptics and proponents of aerosol transmission mode, remember, began when a study published on The New England Journal of Medicine has demonstrated how the new coronavirus, in an artificial laboratory environment, was able to remain in the air by aerosol for about 3 hours . And that the viral particles remained infectious , with a reduction in their charge with the passing of the hours. Another study, published on the pre-print site bioRxiv , was conducted during the coronavirus in the Chinese city of Wuhan, where Ke Lan , virologist from the University of Wuhan, examined aerosol samples in and near hospitals dedicated to Covid – 19 , identifying the genetic signature of the new coronavirus . The study, however, did not show whether the collected viral RNA was capable of infecting or not. In an email addressed to Nature , the author nevertheless states that “during breathing or speaking, the transmission of the coronavirus via aerosol could occur and have an impact on people near and far. As a precaution, people in general should avoid crowded places and wear masks to reduce the risk of exposure. “
And again: a study published on Jama , in which the isolation chambers in a Singapore hospital were analyzed, found no evidence of the new coronavirus in air samples, but on some surfaces such as ventilation systems. While, a similar study identified the viral rna in almost two thirds of the air samples collected in rooms of isolation of a hospital and in a facility dedicated to the quarantine of patients with mild infections. None of the air samples, according to the study, was infectious in cell culture, but the data suggest that “the aerosol particles are produced by patients with Covid- 19, even in the absence of a cough “, write the authors. In addition, a research, cited by the American National Academy of Sciences , highlighted how the personal protective equipment (Dpi) could be source of contamination in the air . The researchers, in fact, have discovered how the new coronavirus can be brought back into circulation when health workers remove the Dpi, clean the floors and move through contaminated areas.
But not all scientists agree . WHO experts, in fact, report in a document released on 27 last March that the mode of transmission through the aerosol may only be possible in circumstances and specific contexts , such as the hospitals. As the report points out, “the evidence of the viral RNA is not indicative of viruses that could be transmissible” . The document also highlights how the analysis of over 75 thousand cases of Covid- 19 in China has not shown that it has found coronavirus transmissions via aerosol. “The absence of evidence does not mean that Sars-CoV-2 cannot be dispersed in the air “, refers to Nature Cowling. While Leo Poon , a virologist from the University of Hong Kong, is of another opinion: there are no According to the expert, sufficient evidence to say that the coronavirus is transmitted via aerosol and studies are lacking showing that the virus is contagious in particles of different sizes from the droplets .
So far, in fact, we do not know if patients with Covid – 19 produce enough aerosol to constitute a real risk : a recent study, for example, failed to detect the viral rna in an air sample collected only 10 centimeters from a patient. Another unknown factor is the infectious dose , i.e. the number of viral particles needed to cause an infection, but even how long you remain exposed to it. For some experts, in fact, it is very difficult that these small concentrations of aerosols , also dependent on the right combination of factors such as drafts, humidity and temperature, could lead to an infectious dose .
Although the results of the studies are not conclusive, the assumption specifies Julian Tang University of Leicester, UK, it should be that aerosol transmission is possible unless scientific evidence excludes it, not vice versa. This would lead people to take additional precautionary measures to protect themselves, such as regularly ventilating indoors and wearing masks to reduce transmission. As reported Science , Americans Centers for Disease Control and Prevention (Cdc) they would be preparing to change course, and to recommend everyone to wear masks when leaving home to limit the spread of the virus. And while masks have become mandatory in many Asian countries, in the Czech Republic and Slovakia, in some European countries and in the United States, supplies are scarce. “Masks should only be recommended to the public after they have been insured to healthcare professionals, patients and the most vulnerable people such as the elderly” , concludes Cowling.