This was undoubtedly the week in which the aerial spread of the coronavirus became an important topic in the public discussion on the fight against Covid-19.
Over 200 scientists from all over the world have delivered a letter to the World Health Organization, urging her to take the mounting evidence that the coronavirus is transmitted through the air seriously.
WHO he acknowledged that further research is needed "to urgently investigate such cases and evaluate their significance for the transmission of Covid-19".
"I honestly don't know what people are waiting for", he claims Chad Roy, a microbiologist at Tulane University in the USA. "The WHO does not need to state that it is an airborne disease to confirm this. In terms of scientific evidence, it is as clear as there is."
Airborne spread of the coronavirus: is it really "airborne"?
What does "airborne" really mean in this context? It's basically a size problem. Studies seem pretty sure that SARS-CoV-2 spreads through tiny droplets that contain viral particles capable of causing an infection.
For an airborne virus, however, this has different meanings, depending on the expert you are talking to. It typically means that it can spread by inhalation of small particles known as aerosols over long distances, perhaps even across different rooms.
For this reason, in terms of the airborne spread of Covid-19, when some professionals are asked if the virus is dispersed in the air, the answer is No. We are not seeing the transmission over that type of distances.
There is debate, however, also on the meaning of "aerosol"
The droplets carrying viral particles in the air can be of any size, but while the larger ones will quickly fall to the ground or other surfaces, the smaller ones (only a few microns in diameter) will remain in the air for a while, with the risk to inhale them.
The word "aerosol" is mainly used to describe these smaller particles.
If SARS-CoV-2 is airborne, it is far from the only disease of its kind. Measles, for example, is known to be able to last in the air for up to two hours. Tuberculosis, although a bacterium, can to remain in the air for six hours.
Evidence of the aerial spread of Covid-19 however, as the microbiologist says, already seems to be a lot.
Several great studies indicate, among the main routes of spread, the fact that the coronavirus remains in the air. Other studies have suggested that the virus can remain in aerosolized droplets for hours.
Finally, the new study conducted by Roy and his team in Tulane shows that SARS-CoV-2 infectious aerosolized particles they could actually linger in the air for up to 16 hours and maintain infectivity much longer than MERS and SARS-CoV-1.
We still don't know what this "aerial advantage" gives SARS-CoV-2. But it could be one of the reasons this is a pandemic, and not just a small outbreak like any other coronavirus.
If the coronavirus is in the air how do you stay safe?
Whether the virus is airborne is not just a scientific question. First of all, it would mean that in places where the virus has not been adequately contained (for example, the US), the economy must reopen more slowly, based on stricter regulations with more careful health practices.
It would mean that our current tactics to stop the spread are not enough.
Roy would like to see much more rigor on the use of masks outside the home. "This virus spreads rapidly," she says. “And the mask can do a lot to interrupt its transmission. I think anything that can stop aerosol production in the environment is useful ”.
With all the limits of the case
We know that although masks can limit the spread of larger particles, they are less useful for smaller ones, especially if they are not worn well.
"I wish we would stop relying on the idea that the masks will solve everything and flatten the contagion curve," says the microbiologist. "It's a magical thought. It won't happen." For masks to make a real difference, they should always be worn, even in the family. And it is almost unthinkable, certainly impossible.
However, all the evidence from many, many studies tends to conclude that airborne transmission is "the primary and perhaps most important mode of transmission for SARS-CoV-2".
In this case, the time and effort dedicated to sanitizing every single surface over and over again has been a great waste of time. "We don't have to worry so much about cleaning every single surface we touch. The focus should be on other factors, like where we spend our time," says Roy.
One of the biggest questions we still have about Covid-19 is the amount of viral load needed to cause the infection.
If the coronavirus is in the air the answer changes: smaller particles will not carry a viral load as large as larger ones, but since they can linger in the air much longer, it may not matter - they will accumulate in larger concentrations and they will distribute more widely and for longer.
The more people who enter and leave an interior space, the more likely it is that someone infected will show up. The longer infected individuals spend in that space, the greater the concentration of viruses in the air over time.
This is particularly bad news for the spaces where people gather for hours and hours, such as restaurants, bars, offices, classrooms and churches.
Air transmission does not necessarily mean that these places have to remain closed (although that would be ideal): but cleaning the surfaces with a disinfectant and having everyone wear masks will not be enough.
To reopen safely, these points will not only have to reduce the number of people allowed inside at any given time,
they will also have to reduce the time people spend there.
Ventilation should also be a higher priority. This will be a big deal for older buildings which usually have worse ventilation systems, and areas with many of these may need to remain closed for much longer.
The impact of asymptomatic spread (transmission from people who do not feel ill) and superscoverers further exacerbates the problem. But (here is, finally, good news) one Research conducted by the United States Department of National Security showed that in the presence of UV light, aerosolized particles of the size studied by Tulane researchers they would disappear in less than a minute.
Well, then, i robot with UV located in hospitals, shopping malls, shops and stations to sanitize environments.
For many places, the damage of the economic closure could be too high a price to keep the virus in check. The best strategy would be to behave as in the early lockdown periods. It's possible? It's impossible?
The constants, in any case, must always be the same, if you want to contrast the aerial spread of Covid-19.