The distance of two meters to prevent contagion by SARS-CoV-2 is an arbitrary measure, suggests a study released this Tuesday, which indicates that the airborne transmission of the virus is very variable and can exceed that distance.
The conclusion is from a study published this Tuesday in the scientific journal Physics of Fluids which points out the ineffectiveness of social distancing per se to mitigate the spread of the coronavirus responsible for covid-19.
Using a computer modeling method to quantify how the droplets spread when we cough, the team of engineers at Cambridge University concluded that, without a mask, a person with covid-19 can infect another at a distance of two meters, even when open air.
On the other hand, coughing also varies, so researchers suggest that the safe distance could be anywhere from one to three or more meters, depending on the risk tolerance of the health authority that sets the rule.
“Part of the way this disease spreads is virology: the amount of virus we have in our body, the viral particles we expel when we talk or cough. Another part is fluid mechanics.”, explains Shrey Trivedi, from the Cambridge Engineering department, quoted in a statement.
It is through fluid mechanics that researchers look at SARS-CoV-2 in this study to understand what happens to droplets after they are expelled.
“As fluid mechanics specialists, we are the bridge between sender and recipient virology and can help with risk assessment”, he adds.
It was precisely this bridge that the researchers sought to measure through various simulations in which they quantified the droplets that would reach another person, compared to the totality of emitted droplets, and what their size would be as a function of time and space.
In these exercises, they concluded that there is no abrupt break from two meters: If the person who coughs is not wearing a mask, the larger droplets fall on nearby surfaces, but the smaller ones spread easily, depending on how quickly and the distance from the quality of ventilation of the space.
Therefore, the team of engineers concludes that social distancing by itself is not an effective mitigation measure and emphasizes the importance of vaccination, space ventilation and the use of masks.
Still, there’s also a high degree of randomness, says Shrey Trivedi, explaining that “each time we cough, we can emit a different amount of fluid, so if a person is infected, they can emit many or few viral particles.
“Even if the same number of droplets are expelled every time you cough, there will be fluctuations because the flow is turbulent”, adds another researcher, Epaminondas Mastorakos, who led the study, explaining that fluctuations, in speed, temperature and humidity, imply that the number of droplets projected at two meters always differs.
In view of these results, the researchers warn that, despite being an effective message for the public, the distance of two meters cannot be seen as a safety mark and, as a mitigation measure, it must be complemented by others.
“We are all desperate to see an end to this pandemic, but we strongly recommend that people continue to wear masks in closed spaces such as offices, classrooms and stores.”, affirmed Epaminondas Mastorakos.
The same team will now continue to develop this work with similar simulations for other types of spaces, such as classrooms, to assess the risk as people spend more time indoors.