The coronavirus persists in the air for HOURS because Covid is airborne, Dr Denise Dewald explains in an important, potentially lifesaving piece.


First published in August 2021.


The coronavirus persists in the air for HOURS because Covid is airborne.

Why doesn’t the CDC do a better job getting this information out? That’s a great question. They created a little lie that it was droplets because they didn’t have PPE 18 months ago. And they kept running with it (the Chinese told us it was airborne in January 2020).


Aerosols that carry the virus can float in the air for HOURS. Long after an infected person has left the room, the air is still not safe to breathe, unless there is aggressive ventilation and filtration to keep it safe.

Just because you are alone does not mean you are safe.

Do not take your mask off inside, even if you are alone. It is not safe for you. And if you are infected, you will be making the air unsafe for others.


Aerosols are tiny droplets produced in your respiratory tract during breathing, speaking, etc. Viruses attach to them, and this is how COVID is spread. The virus is not free-floating in the air, so all the anti-maskers who say masks can’t work don’t understand the science.


The ones produced by breathing are the smallest. Small aerosols are most likely to persist in the environment and most likely to make it to the smallest of another person’s airways. Quiet breathing produces smaller amounts than other expiratory activities.


Talking produces a lot more aerosols that are larger, as well as droplets. These can quickly evaporate down to small aerosols in dry air. Masks help to contain the large aerosols and prevent this.

Small aerosols are really bad because they can penetrate the lungs deeply. If the virus makes it to the smallest of your airways, it is more likely to cause severe disease. The virus that lands in your nasal passages is less likely to cause severe disease, and it will take more virus there to get you sick.


The more virus that gets to your lungs, the worse off you will likely be.

You really want to avoid getting the virus deep down into your lungs.

N95 masks filter out these small infectious aerosols that carry the virus. Simple facemasks do not do this well because of leaks.


Wear an N95 or the roughly equivalent FFP2, KF94, KN95, ASTM3.

It’s critical to have a good seal to the face!

Performance of N95 respirators: filtration efficiency for airborne microbial and inert particles - PubMed
In 1995 the National Institute for Occupational Safety and Health issued new regulations for nonpowered particulate respirators (42 CFR Part 84). A new filter certification system also was created. Among the new particulate respirators that have entered the market, the N95 respirator is the most com…

What about taking my mask off in my personal office space? You might ask.

Don’t do it unless you know that the air in your office is not recirculated with air from other parts of the building. Recirculated air is chock full of other people’s aerosols.


How do you know that?

Ideally, talk with the building engineer. High ventilation can make a big difference by diluting out the aerosols with fresh air. (The World Health Organisation recommends a ventilation rate of 10 litres per second per person).

CO2 detectors can help.


Aerosols can easily spread through air ducts.

SARS spreads via the air ducts and defective sewage traps, leading to a large outbreak in an apartment building in Hong Kong. Buildings need to be designed better for better health and future pandemics.

Now for toilet plumes.

Lidless toilets in public bathrooms contaminate the air and all surfaces with faeces and virus. We need serious mitigation here. So, for god’s sake, DO NOT EVER TAKE YOUR MASK OFF IN THE BATHROOM.


Recirculated air is an aerosol orge, where everyone’s lungs are bathing in everyone else’s aerosols. Practice safe breathing in the time of COVID. Avoid pulmonary promiscuity. Don’t let other people’s aerosols into your lungs, unless they are in your bubble.

Special message to educators: Do not take off your mask to eat lunch in your classroom! Do not take your mask off before or after class. And, most of all, do not take your mask off to speak. This is for your safety and the safety of your students.

Eat lunch outside or in your car. Avoid being downwind of other people. Maintain at least 6 feet of distance outside. Do not eat inside. It is too hard to know if the inside air is truly safe.


We need to break the chain of transmission. 




— AUTHOR —

Dr Denise Dewald, Internal medicine/pediatric (Med-Ped) specialist.


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[This piece was first published as a Twitter thread and turned into the above article on 30 August 2021 with the purpose of reaching a larger audience. It has been minorly edited and corrected, and published with the author’s consent. | The author of the tweets writes in a personal capacity.]

(Cover: Pixabay. / Licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.)

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