Big thank you to @EricCarroll for pointing out this new WHO document on SARS-CoV-2 transmission.
This document is pretty complex, in-depth, dense, and I still expect it to evolve as we learn along the way. They have some of the correct people to be working on this, for once. Hello Lidia Morawska signing off on it at the beginning of the forward.
First, a tldr. If you don't care about how it came to be, or the science, and just want to know the outcome, here it is:
https://partnersplatform.who.int/tools/aria
Go to the calculator, enter your data, and come out with a probability of infection in a given situation along with the number of expected secondary infections from that interaction.
Here's the document itself if you want to follow along:
https://iris.who.int/bitstream/handle/10665/376346/9789240090576-eng.pdf?sequence=1&isAllowed=y
Disclaimer - This is evolving science.
I'm going to split this up in a thread, because I took a lot of notes of what stood out to me on a first read, and I hope to come back to it, and use it as a general reference moving forward.
While not strictly the same document, the WHO this week released a related document bringing new clarity for a(hopefully) shared terminology of airborne infection going forward.
From the executive summary:
"Terminology used to describe the transmission of pathogens through the air varies across scientific disciplines, organizations and the general public. While this has been the case for decades, during the coronavirus disease (COVID-19) pandemic, the terms ‘airborne’, ‘airborne transmission’ and ‘aerosol transmission’ were used in different ways by stakeholders in different scientific disciplines, which may have contributed to misleading information and confusion about how pathogens are transmitted in human populations.
...
The scope of what type of pathogens were covered in this consultation and the resulting
descriptors used in this document are as follows:
• Pathogens, contained within a particle (known as ‘infectious particles’), that travel through the air, when these infectious particles are carried by expired airflow (they are known as ‘infectious respiratory particles’ or IRPs), and which enter the human
respiratory tract (or are deposited on the mucosa of the mouth, nose or eye of another person) and;
• Pathogens from any source (including human, animal, environment), that cause
predominantly respiratory infections (e.g., Tuberculosis [TB], influenza, severe acute
respiratory syndrome [SARS], Middle East respiratory syndrome [MERS]), but as
well as those causing infections involving the respiratory and other organ systems (e.g. COVID-19, measles).
The following descriptors and stages have been defined by this extensively discussed consultation to characterize the transmission of pathogens through the air (under typical circumstances):
• Individuals infected with a pathogen, during the infectious stage of the disease (the source), can generate particles containing the pathogen, along with water and respiratory secretions. Such particles are herein described as potentially ‘infectious
particles’.
• These potentially infectious particles are carried by expired airflow, exit the infec-
tious person’s mouth/nose through breathing, talking, singing, spitting, coughing or
sneezing and enter the surrounding air. From this point, these particles are known as ‘infectious respiratory particles’ or IRPs.
• IRPs exist in a wide range of sizes (from sub-microns to millimetres in diameter).
The emitted IRPs are exhaled as a puff cloud (travelling first independently from air
currents and then dispersed and diluted further by background air movement in the room).
• IRPs exist on a continuous spectrum of sizes, and no single cut off points should be
applied to distinguish smaller from larger particles, this allows to move away from
the dichotomy of previous terms known as ‘aerosols’ (generally smaller particles) and ‘droplets’ (generally larger particles).
• Many environmental factors influence the way IRPs travel through air, such as ambi-
ent air temperature, velocity, humidity, sunlight (ultraviolet radiation), airflow distri-
bution within a space, and many other factors, and whether they retain viability and infectivity upon reaching other individuals.
...
The descriptor ‘transmission through the air’ can be used to describe the mode of trans-
mission of IRPs through the air.
Under the umbrella of the ‘through the air’, two descriptors can be used:
•
‘Airborne transmission/inhalation’: Occurs when IRPs expelled into the air as described above and enter, through inhalation, the respiratory tract of another person and may potentially cause infection. This form of transmission can occur
when the IRPs have travelled either short or long distances from the infectious person. The portal of entry of an IRP with respiratory tract tissue during airborne transmission can theoretically occur at any point along the human respiratory tract, but preferred sites of entry may be pathogen specific. It should be noted that the dis-
tance travelled depends on multiple factors including particle size, mode of expul-
sion and environmental conditions (such as airflow, humidity, temperature, setting, ventilation).
•‘Direct deposition’: Occurs when IRPs expelled into the air following a short-range
semi-ballistic trajectory, then directly deposited on the exposed facial mucosal sur-
faces (mouth, nose or eyes) of another person, thus, enter the human respiratory tract
via these portals and potentially cause infection."
https://iris.who.int/bitstream/handle/10665/376496/9789240089181-eng.pdf
I have done you all a disfavor by putting these two documents in the same thread, but what's done is done. I'm going to try to make this clear.
These are NOT the same documents. One is about only COVID:
https://iris.who.int/bitstream/handle/10665/376346/9789240090576-eng.pdf
One mentions COVID, but is about ANY airborne pathogen:
https://iris.who.int/bitstream/handle/10665/376496/9789240089181-eng.pdf
All day every day I see people taking quotes from the second one and talking about how absurd it is to say that about COVID, and every time I look, the document's not actually talking about COVID where they quoted from.
I know this won't stop any of it. It's far from a perfect document and that could be discussed. There's plenty there to disagree with, but, I'd say 90% of the discussion about it that I've seen to date has been uninformed and/or disingenuous.
I have chosen to die on this hill, and so I will continue. I was going to ignore this new opinion piece in The Lancet, but, I can't help myself in the end.
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(24)00244-7/fulltext
The first time I read it I gave up on the first paragraph.
Read this carefully:
"The report proposes that use of the unqualified terms airborne and airborne transmission in the context of infectious disease transmission should be avoided."
Followed by:
"It introduces new terms matched to specific definitions, including “through-the-air transmission”, “infectious respiratory particles”, “airborne transmission/inhalation”, “direct deposition”, “semi-ballistic”, and “puff cloud”. "
What this, literally, says is that we should replace "airborne transmission" with "airborne transmission/inhalation." This is what everyone is fighting over.
After it came across my timeline for the 20th time I decided I'd give the rest a read.
Paragraph two. Two examples of airborne being used in papers in the last 127 years to show that there was no confusion regarding the term "airborne"?
Compare that to the extensive writing of Prof. Jimenez on the history of the droplet dogma and decide if you think everyone understands this.
https://royalsocietypublishing.org/doi/full/10.1098/rsfs.2021.0049
https://onlinelibrary.wiley.com/doi/full/10.1111/ina.13070
Paragraph 3. Finally something we agree on. The WHO botched the last 4 years horribly.
The next paragraph is where this falls off the rails for me.
"This new WHO report appears to assume that because some infectious disease experts believe that the SARS-CoV-2 virus is airborne only “situationally” (ie, under unusual conditions),1"
I, for one, read this and went directly to the report itself because I was appalled. Guess what? The quoted word, "situationally", never once appears in the document, which is cited. Nor does "under unusual conditions." So now it's just quoting things that don't exist and citing them.
To be clear, it's citing a document titled "Global technical consultation report
on proposed terminology
for pathogens that transmit
through the air" not the document actually about COVID(https://iris.who.int/bitstream/handle/10665/376346/9789240090576-eng.pdf), while complaining about COVID.
I don't see a need to continue.
Mark my word. The CDC delayed their response to this document, whether or not they would go along and declare COVID airborne, because people are making it "controversial" and giving them cover to.
The WHO - COVID is not airborne.
Everyone for 4 years - Declare it airborne!
The WHO - Here's a 66 page document painstakingly detailing how COVID is airborne titled "Indoor airborne risk
assessment in the context of SARS-CoV-2" followed by a 33 page document bringing the droplet people and aerosol people under one umbrella explaining how droplets can go through the air and be deposited AND aerosols can fly long distances through the air. To make both happy we'll put transmission in two subcategories:
Airborne transmission/inhalation and direct deposition.
Everyone - No, not like that!
@BE Oh for pete's sake.
@BE 💧️also the WHO: [upgrades all their ventilation]
No one can justify their initial response.
@BE 💧️ because it's unjust
Correct. I have yet to see anyone argue they did the right thing.
@BE 💧️ those we charged with our protection threw us to the dogs the moment the SARS they'd supposedly prepared for actually arrived
Yes, I couldn't agree more.
So, rather than being happy that the WHO has put the aerosol people in charge, at least enough to acknowledge airborne transmission FOR ALL PATHOGENS going forward, and then pushing the CDC to make the same admission, we're instead going to quibble with terminology and give the CDC cover to ignore it?
@BE 💧️ does cover matter when public health is basically dead? the public doesn't trust these orgs anymore, and it seems that droplet precautions are what will be recmmended for anything that "travels through the air"
bird flu's gonna be real interesting, that's for sure
I guess you're asking me if I care whether there's pressure on the CDC to accept airborne transmission of pathogens?
I do, because change is only going to happen through insurance actuaries and courtrooms. The CDC declaring airborne transmission would eventually end in airborne precautions. The CDC citing "disagreement in the scientific community" and refusing to acknowledge airborne transmission will end with zero precautions.
I don't accept that public health is *eternally* dead. Progress is progress.
@BE
They're being so nit-picky because they want to dismiss research that doesn't use their terms from consideration. It's a way for them to control the narrative.
@BE that "cover" they've been given extends to some of the soft and manipulative language in those original HICPAC guidelines proposed last year.
Airborne was in fact mentioned in there... but presented in such an extraordinary way (with technical emphasis on isolation rooms, negative pressure chambers, and full body suits) as to make any implementation of it untenable or wildly impractical. Like, they could have just said "open window, check HEPA filter, were a respirator" but no. 😒
Yeah, same thing with the latest CDC "respiratory virus prevention" guidance. It isn't atrocious, they do at least discuss some good things(https://qoto.org/@BE/112037743174022489), but what dismayed me is that they put that stuff out on March 1st, but then after the WHO put out their documents the CDC said they were delaying responding to it, probably until 2025, and probably wouldn't be further updating anything in 2024. I don't know if that's just an election year thing or what, but, it seems unnecessarily political, rather than science driven.
I think this article from Scientific American does a great job of laying out some of the reasons these documents are important.
https://www.scientificamerican.com/article/a-fight-about-viruses-in-the-air-is-finally-over-now-its-time-for-healthy/
"The operative phrase here is “through the air.” It’s plain language that anyone can understand, and this switch from jargon such as “airborne” and “aerosol” may finally clear the way for researchers to get funding to study better, real-life ways to protect people from a range of infectious diseases.
And just maybe governments, retailers, school authorities and others can now start to get solid information about ways they can clean indoor air. While it is going to take more than a wordy WHO statement to persuade gym owners that fogged-up windows mean too many people are huffing out potentially infectious air, the new wording does provide a better explanation of why it’s gross and unhealthy."
...
"This should clear the way for funding more and better research on the transmission of infectious diseases—not just COVID, but influenza, respiratory syncytial virus (RSV) and viruses that cause the common cold. That, in turn, should give managers of schools, retailers, airports and other public spaces the information they need to help keep air and surfacers cleaner. Because if people understand the physics of disease transmission, they can find ways to safely keep schools, shops and restaurants open during outbreaks and epidemics with better practices in ventilation, air and surface cleaning and foot traffic control."
...
"“It’s now respectable to do this research,” Jiménez said. “People can get funding to do some research about indoor air and engineering systems. They are stepping into fields that they really wouldn’t work on before. So you see some encouraging changes.”"