The infectivity of the SARS-CoV-2 coronavirus is reduced by 90% after 20 minutes of its emission through the tiny particles of gas and liquid exhaled when we speak or breathe (theaerosol). Much of this loss of ability to infect occurs in the first 5 minutes of coronavirus exit from the airways: this is supported by a study from the University of Bristol (United Kingdom) which reiterates the importance of masks and spacing in the prevention of CoViD-19 .
A short distance away. Much emphasis has so far been placed on the importance of good ventilation of closed and crowded spaces; but according to the new analysis still awaiting review, the most risky situation is that … nearest. “If I have lunch with friends in the pub, the main danger is that I pass the coronavirus to my friends or that they pass it on to me; and not that the infection comes from someone sitting on the other side of the room, “explains Jonathan Reid, director of the Aerosol Research Center at the University of Bristol.
A more precise approach. That of Reid and colleagues is certainly not the first simulation of the diffusion in the air of infected aerosols. This time, however, instead of spraying viral particles into a sealed, rotating chamber (a “standard” technique in this type of study, which allows aerosols to be kept suspended), the team tried to replicate exactly what happens to aerosols one time they leave the “warmth” of the respiratory tract.
The researchers set up a nozzle capable of releasing a precise and studied number of aerosols, which were left to levitate between two electric rings for a period of between 5 seconds and 20 minutes. The device also allows you to adjust temperature, humidity and light to understand how these conditions affect the stability of the particles – and consequently the survival of the coronavirus. Once done, the remaining viruses are extracted and transferred to cell cultures, to understand if they are still capable of infecting.
What it turned out. When the aerosols carrying the coronavirus leave the lungs, a humid, CO2-rich environment, they quickly “dry” and undergo a rise in pH. These two changes destroy the pathogen’s ability to infect human cells. How quickly this happens depends on the relative humidity conditions of the surrounding air (and, importantly, not the temperature: it is not true, therefore, that high temperatures kill SARS-CoV-2).
In conditions of relative humidity below 50%, equivalent to the dry air in many offices, the coronavirus lost half of its infectious capacity in 5 seconds and another 19% in the next 5 minutes. With 90% humidity – as in the shower area of gyms – the loss of infectivity was more gradual: after 5 minutes, half of the aerosols still contained a viable virus, but after 20 only 10% of particles were still infectious.
Use all available sizes. Hence the importance of masks and physical distancing indoors: “When you move (from a positive person) not only are the aerosols diluted, but the virus is also less dangerous because, having passed some time, it has lost infectivity” he explains Reid. It does not mean that the infection cannot occur even at a distance of meters: it happens, but it is more difficult. The situations most at risk are those of close proximity with an infectious individual. The above applies to all old coronavirus variants. The team is now preparing to study Omicron as well.
Ventilate the premises. Adequate ventilation helps, because if the virus carrier remains in the room, viral particles accumulate over time. But alone is not enough: taken individually, none of the anti-covid measures protect sufficiently.