Since the start of the pandemic, WHO has argued, based on previous evidence, that SARS-CoV-2 is transmitted by microdroplets and is not airborne. At the beginning of July, this statement changed.

Under pressure from more than two hundred researchers, they reluctantly warned that it could also be transmitted by aerosols, through the air. After a recent article, the hypothesis that supports its airborne infectious capacity seems to gain inertia. What do we know about it?

Microgouttelettes et sprays

SARS-CoV-2, like other coronaviruses, has been known from the beginning to be transmitted by droplets. These are very small and occur when we speak or breathe out. The microdrops quickly fall to the ground or other surfaces, leaving their viral load wherever they land.

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On another side, aerosols are even smaller droplets that can stay in the air, floating and traveling long distances. These, being smaller, contain less viral load, but can be much larger. For months, the possibility of this coronavirus being transmitted by aerosols has also been on the table.

But what difference is there between the two? In reality, there is no clear definition between the two. According to engineer Linsey C. Marr, who has studied aerosols and their implications for health, there is no clear WHO definition, either in size or in other aspects, that allows us to distinguish the two terms.

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Thus, microdroplets can travel several meters before falling, just as aerosols can be kept close to the person, without having to travel long distances, to give a few examples. This makes it very difficult to determine whether we can consider SARS-CoV-2 to be an airborne virus. or only micro-drip.

What do we know so far?

The first thing, as we said, is that we are sure that the virus can travel up to a meter and a half (or maybe more) through microdroplets that can have enough viral load to infect a person. These droplets can contaminate various surfaces that could help spread through contact. So far we are clear.

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Can the virus travel further or stay suspended in the air? According to more than two hundred researchers, who have been lobbying the WHO since early July, there is evidence that the virus could also be transmitted by aerosols. This means that it could travel in the air for tens of meters or more. It could even be kept in areas with no current.


For example, a study, recently published by the University of Nebraska Medical Center, demonstrated the possibility of viral contamination caused by “natural” aerosols (generated by speech and respiration). In the study closed environments have been analyzed, such as rooms and rooms in health centers. However, this evidence is not yet strong enough to understand all the aspects and implications of this fact.

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The fact that there was a possibility of contamination by droplets or aerosols in closed and loaded spaces was already taken for granted (and the pandemic was almost warned from the start). What are the implications of contamination from aerosols or microdrops, if it is even easy to define their difference? The WHO and researchers defending aerosol expansion agree on one thing: even more evidence is missing.

In search of real scenarios

The question is understand how a virus is transmitted in real spaces and situations. For example, in light of all of the above, we can safely say that it is advisable to maintain extreme care in closed and crowded spaces, such as a hospital room. In these, viruses could stay in the air for hours.

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And in other places? This is where we still need evidence the most. For example, proponents of airborne transmission of SARS-CoV-2 point to a case (the study of which has not yet been peer reviewed) in which two carriers infected nine people via the route. air, by aerosols, in a restaurant by the action of air conditioning.

Can viruses be transmitted by other routes? For example, through vents or when passing through a large room… We don’t know yet, at least with absolute certainty. This, we insist, is where there is still a lack of evidence, and this is why the WHO, although it has pointed out the possibility, is still hesitant to give a clear answer.

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It is clear that there are reasons to suspect the possibility that the virus is transmitted by air (by aerosols), which would imply a greater infectious capacity. Little by little, the situation is changing the way virus control measures are reviewed, but it is too early to see for sure where it will.

Images | Unsplash

Source : Engadget