Something’s in the Air (The Airborne Transmission Error)

Written By Daniella Barreto

This episode won Gold at the 2025 Signal Awards for Best Education Podcast and Silver for Best Science Podcast.
It also won Gold at the 2025 W3 Awards in Science & Technology - Individual Episodes & Specials.

Episode three

How a mixup about airborne transmission led to one of the biggest public health errors in history—and how we can change course.

Do you hear a cacophony of coughing? A symphony of sneezing? It's a pathogen palooza out there! A lot of disease transmission happens through the air we share – and most people don’t know. 

Explore how a mixup about airborne transmission led to one of the biggest public health errors in history. Over the last century, our growing understanding of pathogens and the ways they spread allowed public health to mitigate, eliminate, and even eradicate diseases in many parts of the world.

We thought we knew it all. But pride comes before a fall.

Public health has been missing a big part of how diseases like COVID spread and it's cost us a lot. Especially in the last 5 years.

Learn how a group of aerosol scientists teamed up with Dr. Katie Randall, a medical rhetorician and historian, and toppled the house of cards holding up the dogma that droplets are the main route of respiratory disease transmission. How did public health leaders dismiss airborne transmission for so long even though we've known about it for TB, measles, and SARS for decades?

And now that scientists understand so much more about how diseases spread, how can public health adapt to protect us? Dr. Al Haddrell, an aerosol scientist, walks us through how aerosol works and how we can interrupt disease transmission with new knowledge (helped along by Optimus Prime).

Something’s in the air... and it might be a paradigm shift.

 

Machine used for the CELEBS technique (controlled electrodynamic levitation and extraction of bioaerosols onto a substrate) | Image from Dr. Haddrell

 

Spotted a CELEB in the wild!

Ep3: Something’s in the Air

How a giant mixup about airborne transmission led to one of the biggest public health errors in history.

RESOURCES

EPISODE CREDITS

Public Health is Dead is created, hosted, produced, written and edited by Daniella Barreto. 
Music, sound design and mixing by Alexandria Maillot.
Fact checking and production support from Anika Sharma.
Editing support from Kevin Ball, Sophie Kohn, Anika Sharma and Lauren M.

Public Health is Dead runs on listener support! If you’d like to contribute to ongoing production of Public Health is Dead, please support the show!

This episode won Gold at the 2025 W3 Awards for Best Individual Episode - Science & Technology

 

  • DANIELLA: You may know the classic Greek myth of Icarus? 

    TL;DR a young guy and his dad were locked away in a tower because the King thought they’d shared some juicy state secrets about a labyrinth. I don’t know if they did, I wasn’t there. 

    But the dad was a master craftsman and MacGyvered some wings for himself and his son, Icarus, so they could escape. The wings were made of beeswax and sandal straps and feathers. 

    The dad said: “Don’t fly too low, the feathers will get wet and… you’ll drown. 
    But don’t fly too high because the sun will melt the wax and …you’ll still drown.”

    So what did Icarus do? Flying was fun! He got cocky and flew way too high.  


     

    The wings melted and he tumbled into the sea 



    …to his fateful end. 

     

    Why am I telling you this myth? 

    Because, public health as a field did the same thing. 

    This is the story of how we flew too close to the sun. 
     

    Hi! I’m Daniella and this is Public Health is Dead – a eulogy for a job well failed and a gathering of voices to plot what we do next. 

    When you’re out in public do you hear a cacophony of coughing? A symphony of sneezing? 

    Turn on a podcast and hear that the host sounds super congested and croaky? 

    I hear distressed parents talking about how their kids are passing various flavours of illness between each other at school and bringing it home even with “enhanced cleaning procedures” and washing their hands all. the. time. 

    Handwashing, which is common public health guidance (and should be a given) doesn’t really seem to be stopping us from getting sick. 

    I’m sure you’ve seen the news lately… TB, measles, norovirus, H5N1, influenza, walking pneumonia and the steady presence of COVID… it’s a pathogen palooza. If you’ve ever wondered about the definition of an “omnishambles” -- this is it in public health. With ALL the bells and whistles. 

    The Trump administration has pulled the United States out of the World Health Organization and RFK Jr (famously anti-science) is heading up the department of Health and Human Services, the department that makes a lot of public health decisions. YIKES!

    While all this is a loud funeral knell, these changes are only the most recent scene in the death of public health. There were a lot of nails in the coffin that got us here in the first place.

    Today – one of them: a longstanding mistake that may well be one of the largest errors in the history of public health… and during the ongoing COVID pandemic many leaders have doubled down on it. 
    That’s right, we’re going to be talking about airborne disease transmission.

    DR. KATIE RANDALL:  there was confusion over what we considered droplet-based infection versus what we considered airborne-based infection, and it really hinged on the size of particle that was infectious.

    DANIELLA: This is Dr. Katie Randall – the person who toppled the house of cards holding up the distinction between airborne or aerosol transmission and droplet transmission in public health. For context, aerosols are really tiny particles of respiratory fluid, smaller than what we define as droplets, but they can float in the air and be inhaled. Disease-causing microbes are even smaller and can travel in these aerosols between people.

    DR. KATIE RANDALL:  in order to be considered an airborne, an aerosol, uh, in the popular public health, uh, and medical, uh, literature, a particle had to be under 5 microns in size. And things above that were considered droplet based. And those of course have different disease mitigation measures. So that was really the crux of it. 

    DANIELLA: Exactly: public health guidance for interrupting disease spread is different depending on the way transmission happens. 

    Dr. Randall is a medical rhetorician and historian based in North Carolina. When people hear “rhetoric” they often think of the world of politics and persuasion but Dr. Randall’s work was really focused on language and how the words we use influence real life. In this case, our health. 

    Dr. Randall was in the business of forensic citation,She figured out how the language for disease transmission in public health came to be, and how it directly affects our lives today.

    For most of modern public health’s existence, airborne transmission has been feared, mocked, or dismissed and there’s a lot of resistance to acknowledging it. 

    Not to be all “they don’t want you to know” but… public health organizations haven’t been very forthcoming with information about airborne transmission. And dragging their feet has cost us a lot. In human lives, our collective health, and trust in public health as an institution.

    At this point, the evidence for airborne transmission keeps piling up for many diseases and it’s getting hard to ignore. There’s not really a helpful distinction between airborne and droplet transmission. 

    We might be at the precipice of understanding that airborne transmission accounts for more disease spread than we thought. Like A LOT more. 

    Public health leaders have been making decisions on the assumption of droplet spread for most diseases which doesn’t actually hold up against what aerosol scientists see and doesn’t really line up with the scale and speed of transmission for many diseases.

    DR. KATIE RANDALL:  a group of aerosol scientists were like, Where did this 5 micron distinction come from? This doesn't really seem to make sense. And like, cue my research…

    In this episode we’re going to find out where that distinction even came from in all of Dr. Randall’s citation excavation. We’re also going to meet an aerosol scientist, Dr. Al Haddrell, to learn more about disease-causing microbes trapped in aerosols. And finally - the obvious question once we understand how something is making us sick - how do we stop it?

    Chapter 1.YOU ARE HERE; THE PROBLEM

    In our mission to vanquish disease and create a world of our own design free of preventable illness and death, we thought we knew it all. 

    Globally, we’d stamped out diseases like smallpox, we’d eliminated TB, measles and polio in many regions, things were looking like the flying cars and lush forests version of the future; not a tire-fire-dust-apocalypse future….

    We thought we knew everything about how diseases spread and thought we could ignore physics. Well… physics doesn’t like to be ignored. It eventually catches up.

    Bad public health decisions played a huge role in unnecessary death and disablement of millions of people by sticking to wrong ideas about how COVID and other diseases spread and worse? Doubling down, making people really confused. 

    When you’re on the wrong train going in the wrong direction, you get off and get on the right one, right? It’s a lot faster to get back on track the sooner you do that. 

    Well we’re all still waiting for our leaders to do that. Acknowledging that public health advice has not been completely correct is the first step towards updating our knowledge and building a way out of the pathogenic pandemonium in front of us.

    Hop aboard my friend! Our train to paradigm change is here. 

    DANIELLA: For many of us who have access to clean water, plumbing and sanitation, vaccinations, health education, things were pretty good overall. 

    Public health was doing its job, running quietly in the background, and many of us didn’t have to worry about dying of dysentery. 

    I say “many of us” because even in Canada in 2021 there was literally a shigella outbreak (that’s the pathogen that causes dysentery) in the downtown eastside, a neighbourhood over from mine, where many of our unhoused neighbours don’t have access to basic necessities. There was another shigella outbreak among unhoused people in Toronto in January 2025. That’s a policy failure. Shigella is pretty easy to avoid with things like clean drinking water and good sanitation systems.

    For most of us living in the Global North, public health did things that were never before possible without major advances in science and technology. 

    It also meant that public health developed an arrogance problem. 

    And hubris kills. Ask our friend Icarus. 

    We thought the people who came before us were benighted peasants who couldn’t possibly understand the implications and intricacies of bacteria, viruses without the power of the microscope. 

    But that’s just not correct. 

    A lot of Indigenous Peoples around the world had already developed different ways of preventing infection and mitigating disease (e.g. a type of fermented wine made from bananas was used as a sanitizer and allowed for C-sections to be performed as early as the 1800s in Uganda or some First Nations used alder bark as an antimicrobial to treat tuberculosis. Some of these things were known.)

    In my experience studying public health and epidemiology first as an undergrad and then in grad school, it was almost part of the curriculum for the lecturer to bring up miasma theory for a ritual mocking of how silly we used to be. 

    What is miasma theory? You know the smell of rotting meat, decaying food, or a rank garbage can on a hot day? 

    For thousands of years, people believed that nasty odours in the air spread sickness and disease. Before about the middle of the 19th century, people believed these putrid smells or “poisonous emanations” could waft on the breeze, enter the body, and cause disease. 

    It’s actually where the name for malaria comes from: old Italian for bad air. 
    Mal (like the prefix in malevolent) and aria (meaning ...air).

    So when our professor inevitably referenced miasma theory, the students, including me, would all chuckle, crack open our textbooks to the Modes of Transmission section and go through the list… vector-borne, fomite, droplet etc etc and SOMETIMES-OCCASIONALLY-MAYBE-BUT-NOT-REALLY airborne. 

    We’d rinse and repeat for our tests that airborne transmission theoretically existed  but there were rarely exceptions to droplet transmission of pathogens and that was that. 

    No questions asked. No questions answered. And my universities weren’t alone. 

    This is taught in public health and medical schools around the world: droplet transmission is king.

    Oh and you know there would be a multiple choice question about miasma theory on the test. 

    We moved on from that bad bad-air theory knowing that microbes like bacteria and viruses were responsible for a lot of diseases. 
    The thing is, we’ve known that these microbes that cause disease CAN also spread through the air. As airborne particles. For decades. And if we want to be nitpicky about it, technically droplets have also always travelled through the air.

    While the miasma theory that bad smelling air equals disease is not entirely correct, the physics that allows tiny particles to hang in the air, holding microscopic pathogens that cause disease, really is correct. 

    Maybe our forebears don’t deserve such a round mocking every semester. Especially given how badly we have fumbled COVID transmission.
    There are many pathogens the World Health Organization categorizes as “airborne”, as in spread through the air. Measles, Tuberculosis, SARS1, and despite denying it at first, SARS1’s relative, SARS2 or Sars-CoV-2
    That stands for Severe Acute Respiratory Syndrome-Coronavirus-2… You might better know this one as “COVID”, the disease it causes.  

    DANIELLA: Our public health leaders have clung to the idea that only droplets can spread diseases like COVID through being sprayed when we talk or cough or sneeze. The idea is these spray-borne droplets land directly in noses or mouths or eyes or are transferred there on our hands. That’s what’s drummed into students’ heads in school.

    There are some pretty big implications to saying that diseases are airborne, we’ll get into that later. 

    But this idea that only droplets spread disease influenced a lot of guidance and advice early in the COVID pandemic, including this gem from Canada’s Prime Minister, Justin Trudeau, referring to Canada’s Chief Public Health Officer Dr. Theresa Tam:

    JUSTIN TRUDEAU: “Dr. Tam explained yesterday is that if people want to wear a mask that is okay….. it prevents you from breathing or speaking moistly on them, oh what a terrible image...”

    And many other public health and global leaders continue to confusingly evade the concept of airborne transmission like Dr. Bonnie Henry, British Columbia’s Provincial Health Officer:

    DBH: “So we know this is a droplet spread infection and what that means to us is that means you get it by breathing in the virus in small droplets when people cough and sneeze so you have to be quite close to somebody…it’s not something that is widely spread through the air… so really important is to clean our hands regularly and that kills the droplets, kills the virus” 

    Even if leaders weren’t 100% convinced about airborne transmission at the beginning of the COVID pandemic, they knew that other similar diseases, like SARS 1 and the flu, can be airborne. They could have acted as if it were, just in case, while scientists took a closer look.

    This is called the precautionary principle. We’ll get into this in another episode but the precautionary principle means: in the absence of definitive evidence, erring on the side of caution is the only correct and moral choice for deciding public health measures. 

    The WHO’s tweet saying COVID is NOT airborne is still up and they haven’t corrected it. Dr. Tedros Ghebreyesus, the WHO leader, did initially say it was airborne. In 2020. But he quickly changed his tune when Dr. Michael Ryan, sitting next to him at a press conference, scribbled a note and whispered to him on camera. Ghebreyesus then told us all, with a nervous laugh, that it only spreads by droplets. 

    Weird, no? But that was the direction and still, for the most part, it remains. 

    But why?

    DANIELLA: Like Dr. Katie Randall mentioned at the beginning of the episode, there is this cutoff between what is considered airborne and what is considered droplet. 
    But for some reason that threshold was drawn way too small. At 5 microns. 
    This is the 5 micron error. And it’s had huge consequences because it has been the basis for a lot of public health advice for decades.

    It was just cited and recited over and over again in public health guidance.

    But the threshold was wrong. Why?

    Dr. Randall was called in by some aerosol scientists and they started digging… 

    DR RANDALL:  at the time Being a graduate student and you've just gone through years of people telling you like you don't know enough yet You don't know enough yet. You don't know enough yet. And then you're you're kind of entrusted with this  really big problem and the research for this really big problem. 

    DANIELLA: And it was a REALLY big problem. Was Dr. Randall worried about challenging such a touchy and viciously policed issue in public health? As an outsider, not really!

    DR RANDALL:  I  don't think I was worried about what they might say as much as I was worried about, um, presenting  my skills in my field accurately and in a, in a way that would be, um, productive for future, interdisciplinary and cross disciplinary research…  Where the interesting intersection happens is when our different fields of knowledge and our different ways of knowing can intersect to be helpful. It doesn't mean we need to know everything about the other's field, and we couldn't without going through that same training, but having that ability to figure out, you know, where, um, where do the chocolate and the peanut butter go together to make the Reese's Cup, right?

    DANIELLA: There is a great piece in WIRED, I’ll link to it in the show notes. It changed my whole understanding of this pandemic early on and sparked this episode. It’s called “The 60-year-old screwup that helped COVID kill” - many of you have probably read it already. In early 2021 the journalist, Megan Molteni, spoke to Dr Randal and a handful of leading aerosol scientists including Linsey Marr, Jose Jimenez, Kimberly Prather – all experts who were often dismissed by people in the medical establishment and institutional public health.

    One thing Dr. Randall’s research found was that despite its prevalence droplet transmission has actually been challenged for a long time

    Dr Randall’s readings involved a pair of researchers called William Wells and Mildred Weeks-Wells. Mildred was a physician. William was a Harvard engineer. Beginning in the 1930s, they did a bunch of research into particle size, and were particularly interested in respiratory particles, looking at the opposing forces of gravity, pulling them down, and evaporation, pulling them up. From their work they found that particles bigger than 100 microns sank to the ground in seconds. Particles smaller than 100? Those could float. 

    There’s a big difference between 5 microns, which we have been using as the threshold for being airborne, and 100 microns, which is the threshold they observed almost a century ago.

    For scale, a human hair generally has a diameter between 80 and 100 microns. 
    About half of that, 50 microns, is approaching the size limit of what humans can see. 
    Anything smaller than that we can’t see with the human eye. 

    DANIELLA:  If you have ever been in a dark building like a cathedral with big windows where the sunlight streams in through glass and you can see a bunch of floating dust particles with the naked eye? Those are small enough to float and big enough to see. If something as big as a dust particle you can see can be suspended in the air and be buffeted about by gusts and other movement, surely smaller particles would float just as easily? Likely easier? 

    We’ve been operating on a 20-fold misunderstanding of how big particles can be and still be suspended in the air. 
    5 microns can easily float. So can 6 microns. 7,8, 9, 10 all the way to about 100 microns. The Wellses’ research has been replicated and validated and the generally accepted cutoff for airborne vs. droplet is in fact 100 microns. Not 5.

    Now that that’s sorted…

    The size of aerosols of respiratory fluid that we exhale when we breathe is generally smaller than 5 microns. 

    They’re a bit bigger when we sing and shout. But they’re still under 100 microns. When we speak, for every droplet expelled that is bigger than 100 microns, there are 100 to 1000 times the number of aerosols smaller than 100 microns also expelled.  

    Which, if you’ve been paying attention, means that they can float. And there are a lot of them. 

    These tiny aerosols can carry microscopic pathogens within them. 

    And, because they are floating, not dropping like bigger droplets, they can travel farther than 6ft. 

    Now if you’re the question asking type you might be asking “Wouldn’t that mean a lot of common public health guidance to stay 6 feet apart is simply not correct if we’re trying to interrupt respiratory disease transmission?”
     

    Yup. It sure would!

    Being more than 6 feet apart does give some distance and time for larger droplets or particles to sink but it doesn’t mean we get a magical force field of protection in front of us from airborne aerosols.

    Dr Randall went backwards and forwards through history reading citations, experiments, and public health guidance to figure out where we went wrong. More on what they found after a quick break.

    30s HOST-READ PROMO SWAP FROM rePROs Fight Back PODCAST

    Chapter 2. HOW WE GOT HERE

    In this next part you’re going to hear a few names coming up in the history Dr. Randall combed through but don’t get too hung up on specifics for our purposes. We’re going to trace the broad strokes of how public health got to this place of operating with missing information and an overconfidence that droplets were the cause of all ills. 

    In the early 1900s, there was a prominent epidemiologist called Dr. Charles Chapin. He was very attached to the idea that infection happened person to person through direct contact with bodily fluids or close proximity to spray-borne liquid droplets – and NOT by airborne transmission – because he’d had some success in infection prevention under this assumption that droplets were the cause.

    But the conflation between “close proximity” and an actual mechanism for disease transmission would fog up public health communication about disease transmission all the way to the present day. 

    We’ve all heard unclear terms like “spreads through close contact” …. But it can mean a few things: Is that physically touching? Is that breathing in someone’s face? 

    “Close contact” is more of a reference to distance than an explanation of what actually  happens in that distance to transmit pathogens. ‘Cause in that close distance a lot of stuff can happen.

    An important part of why we’ve been confused and relying on droplet transmission is that when an infected person exhales, the most concentrated aerosol is in close proximity to them. 
    That makes sense, it’s not going to be most concentrated far away from the person who has just breathed out. 

    When exhaled aerosol mixes with the room air it gets diluted gradually. 

    That’s why moving away from the source of infection means the likelihood of transmission goes down but it doesn’t mean that pathogens exist solely in droplets that fall within a couple of metres. That’s a false inference. And it’s one Chapin was convinced was true.

    Chapin became the president of the American Public Health Association in 1927 and, unfortunately for those of us now living through the COVID pandemic, his ideas had been widely adopted, including by the CDC. 

    Airborne transmission was sidelined, and this was still the leading idea at the start of the COVID 19 pandemic…  even though Chapin’s hypothesis remained unproven. 

    There were some industrial hygiene studies in the 1940's that came to the conclusion that nose and throat mucus was good at filtering and blocking bigger particles in people who work in mines and factories. 

    They found that particles of 5 microns and smaller could get deep into the lungs and cause irreversible damage. They weren’t looking at pathogens but that size was notable to Dr. Randall for how small particles needed to be to get deep in the lungs. This was a clue.

    Now here’s where William Wells, comes in again in Dr. Randall’s investigation. He’s that Harvard engineer looking at respiratory droplets and challenged the understanding of airborne diseases. He did an experiment about TB.

    TB, now one of the most widely accepted airborne diseases, was also thought to be droplet spread at one time. 

    In this experiment they sprayed a very fine mist of aerosols, containing TB bacteria, into one rabbit cage and a coarse mist of the same fluid into another. The rabbits exposed to the fine mist showed more than 100 points of infection on their lungs and the ones in the coarse droplet cage had just a few (even though they were exposed to more TB organisms). Interesting. 

    William Wells’ collaborators, Riley and Mills, did another experiment where they pumped a closed system of exhaust air from a TB ward into guinea pig cages. Soon enough, the guinea pigs exposed to the exhaust air had contracted TB. VERY interesting.

    Even with experiments like this, droplet transmission ideas continued to dominate. 

    In 1945, William Wells wrote in the journal, Science, that science had been successful by investing in eliminating water and foodborne infections but we haven’t taken action on airborne infection. 
    I wonder what he’d think today of our inaction, when we have even more evidence now than he ever did.
    Measles, a super infectious airborne disease, transmitted more easily when people are close together, was also considered droplet-spread until as late as 1985. So our understanding and acceptance of airborne transmission even for a few diseases, is really quite new! 

    The Wellses also showed that UV disinfection light significantly cut measles and chickenpox infections when installed in the upper part of a room - that’s where aerosols rising would be deactivated. Disinfecting the air using UV works. But it’s not accessible to everyone. Canada has some strict rules at the moment about commercial far-UV even though it is available in other countries. Maybe that’s an avenue for public health organizations to explore to help interrupt transmission in public buildings.

    Aerosol science continued to evolve faster than public health cared to keep up with, because the field’s was so devoted to droplet spread. 

    They’re doing some cool stuff over there in aerosol science that public health should be paying a lot of attention to. 

    Let’s take a detour and meet someone at the forefront of airborne research. 

    We’ll come back to Dr. Randall’s citational digging and her discovery about why our airborne threshold was so wrong for so long now that you’ve heard some of her trail of clues. 

    DANIELLA: This is Dr. Al Haddrell. He’s an aerosol scientist based at the University of Bristol in the UK but he’s from my neck of the woods in British Columbia. We chatted about how aerosols work.

    DR AL HADDRELL: When you exhale, you basically have this warm, moist air leaving your body. It's got CO2, but it also has a small, you know, few thousands numbers of aerosol particles. And it's warm, and it's breathed into typically a room that's cooler than that. And because the air is colder, you basically almost like form a plume of air that fills the space and sort of goes upwards

    There’s mountains of undeniable evidence available at this point about the physics and chemistry of aerosol transmission. Understanding how to stop transmission means we have to combine our understandings of biology, chemistry, and physics. It’s not really a medical question. But it’s been viciously guarded as one by medical and public health institutions.

    One thing we’ve heard from public health leaders throughout the COVID pandemic is that only aerosol-generating procedures in hospitals are a concern for airborne transmission of disease (these are procedures like intubation, where particles are forced out of the airway)

    But as Dr. Haddrell says, 

    Dr. Haddrell: Well, breathing itself is an aerosol generating procedure.…talking is another aerosol generating procedure. Uh, 

    DANIELLA: And paired with public heath’s incorrect cutoff size for aerosols, that changes a lot about intervention 

    There’s fluid on the surface of our airways, called respiratory fluid, that essentially gets swept up into the air passing over the membrane as we breathe, or talk, sing, or yell… and gets released in a plume of aerosol when we exhale. (Mmm lung juice.)

    Dr. Haddrell: if you're face to face with someone in the, in that plume, the transmission risk is really high. And if you're talking, you're producing way more aerosol.

    Dr. Haddrell: coughing produces as well, but one of the things with COVID, it was the, um, early pre, Pre coughing, pre symptoms was the, was the most infectious time for a lot of people. And so what this means really is the aerosol produced by talking and breathing seems to be the most important in terms of disease transmission.

    DANIELLA: Staying home when you’re sick isn’t the only advice to prevent COVID transmission, then, since we’re infectious before symptoms even occur. It’s definitely good blanket advice. But if we expel aerosol all the time, even before we are coughing or know we are sick, that leaves a lot of opportunities to pass sickness around… like being in an emergency waiting room for hours or being on a crowded bus.  

    Approximately 49% of transmission happens before or without symptoms.

    So even if you’re not yet having symptoms like coughing or sneezing - just breathing, talking, or singing is doing the heavy lifting of passing pathogens from one person to another.

    This is part of why it remains so hard to control COVID transmission. If we wait til we’re sick the horse is already out of the stable by that point. It’s probably already been passed to someone else.

    There are ways to tackle transmission that don’t come too late though.This is why respirators are so helpful. Despite posted public health guidelines to mask as a preventative measure, our leaders continue to dismiss these instructions. It feels like we've reached some unspoken consensus to wear a mask only when you're sick, if that.

    DBH: So yes, masks are important in this but they're important for people to wear if they’re sick…

    Oh wait, it was spoken. This is Dr. Bonnie Henry again:

    DBH: Um we don’t recommend that people who are well wear them because it is not an effective way of protecting yourself
     

    We now know it’s one of the best ways to protect ourselves. Respirators, tight fitting masks designed to block aerosols, work incredibly well when they’re worn properly and consistently. And if you’ve listened to the episode about the Orpheum theatre, you might have some ideas about ventilation, too.

    At the end we’ll run through a list of things that might help get us out of this mess. 

    Aerosol researchers and public health advocates have been ringing the airborne alarm since 2020 and droplet-only spread has been consistently challenged but that’s been swept under the rug for many years. 

    DANIELLA: Now we find ourselves back with Dr. Randall after she’s gone through all that research, double and triple checking citations to try to figure out why our guidance has been so wrong. And they cracked it. They’d put the pieces together and slowly understood why we were using 5 microns as the airborne threshold instead of 100 microns.


    DR RANDALL: I kind of connected these dots of, Oh, I think, I think it came from this conflation of these definitions. … I think it came from like this pathogenesis of tuberculosis becoming the standard, even though that doesn't apply,

    DANIELLA: Basically, it seems like people in public health noted the size of the particle that TB is infectious in, said, hey that size is airborne, anything bigger than that isn’t, and never really revisited the question. Even though it doesn’t apply to everything.

    Tuberculosis, or TB, replicates deep in the lungs where only particles smaller than 5 microns can physically make it. Our lungs are made of branched tubes that get smaller and smaller until they end in miniscule sacs called alveoli. Of course, only tiny tiny tiny particles like some aerosols can make it down there.  

    Dr. Randall found that we sort of held on to that knowledge about TB, confusing/conflating what is respirable, what stays airborne, and what is infectious (in the case of TB), and applied it to a bunch of diseases even though many pathogens can also be airborne but don’t need to be small enough to get deep in the lungs to cause disease. Those particles can be much bigger and still do the job.

    When the pieces started falling into place, Dr. Randall says they didn’t have a eureka moment…

    DR. KATIE RANDALL:  in that grad student humility, at least for me, you don't have this moment of  I'm a genius. Like, I figured it out. It's this more of like  “Okay, now let me make sure no one else has put this together. Let me make sure this hasn't been cited somewhere else. Let me make sure, like, let me take it back to the folks in my research team to see what they think about this” and then me saying like, “I think I, I think I got it. You know, I think I figured this out”. Um, but it not really occurring to me in the moment how insightful that, that insight was, if that makes sense, how impactful that insight was.

    DANIELLA: Yeah. It was hugely impactful. Dr. Randall had basically pulled the rug out from under public health guidance and infection control as we know it today. 

    Nobody had known the reason for the 5 micron cutoff before. Droplets landing accurately on mouths and noses and hands to transmit disease at scale and speed didn’t seem very likely. That’s like throwing a bullseye every time. 
    Smaller aerosol inhaled from constant exhaled plumes in the air we share would make loads more sense. 

    The AIR should be the target for intervention. Everyone would be excited about this realization. Right? 

    DR. KATIE RANDALL:  I thought for sure that because we had like cracked it, that suddenly it would be like, oh my gosh, yes, like of course, of course it's aerosol spread and we are going to change all the guidance and we're going to make sure our definitions are updated and clear and we're going to work across fields to make sure we like, have an understanding, a shared definition of these terms.

    Um, and that, that didn't happen. And I was surprised, but I shouldn't, I shouldn't have been surprised. And I honestly couldn't tell you why I was surprised. I just thought like we worked so hard to kind of  tease this out, um, and then you present it and you're like, here you go, like I did the work for you  and they're like, Mm, maybe, we'll think about it

    DANIELLA: Not a whole lot happened. Talk about anti-climactic. The public health world kind of just shrugged.

    I think our public health leaders have most likely clung to the idea that only droplets can spread diseases like COVID for a couple of reasons:

    1, it’s hard to admit you’ve been wrong and your decisions have contributed to a lot of damage, death and pain. And the long term consequences of wrong guidance are looking pretty ghastly when it comes to Long COVID and other post-COVID health problems. There’s maybe an element of trying to save face.

    2, it’s much easier to tell people: wash your hands and stay at home because that’s something individuals can choose to do and if you get sick, welp, that’s your responsibility. It’s not possible to tell people they’re responsible for choosing which cubic metres of air they breathe, which would mean the government has to ensure workplaces and buildings have clean air. 
    That’s an expensive responsibility that not many people want to take on
    But quietly, things did start to shift a little after Dr. Randall’s discovery

    DR. KATIE RANDALL:   the CDC in, uh, uh, did, then start talking about it being airborne. The WHO did start talking about it being airborne, but it was with no fanfare. Um, like I remember very, very, uh, I think it was soon after our article came out, Dr. Fauci, and I'm not saying that he read our article or that this was why, but Dr.Fauci also started talking about why, about how, you know, there is this acknowledgement of the, this aerosol transmission. So all but all of these things happened without much to do. Websites were quietly updated, um, people just sort of started talking about it more without really acknowledging that they had been like super wrong about it earlier

    DANIELLA: The WHO did update their website. Since 2021 the website has said in no uncertain terms that SARS-CoV-2 spreads between people through airborne transmission. But the WHO and other public health organizations have not clearly corrected this information for the public. They kind of whispered and mumbled it pretty late in the game when it was impossible to deny. If you weren’t paying attention, you probably wouldn’t know.

    DR. KATIE RANDALL: Success was achieved in the sense that people did start talking about aerosol transmission, airborne transmission of COVID 19. Um, it just happened in this very, uh, more subtle, quiet way, um, than I expected. 

    DANIELLA: Ultimately Dr Randall wanted to prove that medical historians had an important role to play in public health

    DR. KATIE RANDALL: …Thankfully, all of the scholars that I worked with were just so encouraging and so, um, so quick to tell me and, and reiterate that this, that it was important to have this perspective, um, and I really appreciate them for that.  And I'd like to see more of that collaboration, um, you know, in other, in other scientific, uh,  lenses and, and, uh, inquiries.

    I think it was a really valuable collaboration.

    DANIELLA: Just like Icarus, we have the information that could save us. 

    Different fields with a lot of expertise are telling public health where to course correct. 
    But many public health leaders have chosen to ignore it so we're all getting burned.

    Chapter 3. THE FINE PRINT (ON THE FINE MIST)

    DANIELLA: How exactly do we study aerosols so we can figure out how to stop them spreading disease? 

    Scientists in the 1950's were interested in airborne transmission, driven by the Cold War and the fear of airborne bioweapons. The methods they used to answer questions about how long biological agents could live in the environment didn’t translate very well to questions about quick transmission of pathogens like COVID, so Dr Haddrell and his team designed a new way to investigate airborne disease transmission

    DR. HADDRELL: So we developed a technique we call CELEBS, uh, it stands for the [00:13:00] controlled electromagnetic levitation. An extraction of bio aerosol onto a substrate. That's a very…

    DANIELLA: That's a mouthful.

    DR. HADDRELL: …exactly what it does. Yeah. It's one of those things, you're writing down these words. You're trying to, you need an acronym for these things. And basically we got the kit built in like April, May of 2020.

    DANIELLA: All their measurement units are named after Transformers. Because early in the pandemic in the UK…

    DR: HADDRELL: …we had to use whatever color filaments we had. And by the time we finished building the 1st unit, I realized I'd used gray, red and blue. And an orientation you look at, and it's like, this looks like an optimus prime transformer toy from the 80s, like G1 transformer.

    So that became the prime, the optimus prime unit. And so after that, we had a trend. So the second one is the Megatron units. Now there's the Bumblebee unit we've got built. 

    DR. HADDRELL: basically what we do is we use, uh, droplet on demand dispensers. So we can, these little tiny things that we can make individual droplets that are like, Microns in size, so very, very small, and we inject them into an electrodynamic field. And so it's like an electric field that we can levitate a small population of particles in. 

    DANIELLA: They can pluck these levitating aerosol particles out of the air, pop them on a cell culture or growth medium, and see how the microbiology has changed. When they’re looking at Sars-COV2, basically, they can see how the inside of the aerosol has changed and if it can infect a cell. 

    DR. HADDRELL:  So basically how it's decayed over time. And really the, the, the, the gimmick behind this is really the high degree of control in terms of what's in the aerosol, the time resolution, the complete, the gas phase composition, we're able to control all of these different parameters to a very high degree

    DANIELLA: Dr Haddrell spends a lot of his time trying to figure out the ways viruses lose their ability to make people sick so we can use that knowledge to tackle them

    DR. HADDRELL:  Really, what I'm trying to better understand is really the mechanism by which these viruses lose infectivity.

    DANIELLA: He and his team found an interesting process that helps SARS-CoV-2 lose its infectiousness in the air.

    You probably have some baking soda at home - that’s another name for sodium bicarbonate, and it helps delicious baked goods get that light airy texture by releasing bubbles of CO2. 

    The bicarbonate in our bodies is also a way to capture and release CO2.

    DR. HADDRELL: when you breathe out, the, you know, the aerosol has a lot of water in it, has a lot of bicarbonate. So the water leaves, everything gets really concentrated. So the salts and everything, which can potentially affect the virus. But what we found with COVID is that that bicarbonate leaves in the form of CO2. And when that happens, that really increases the pH of the aerosol. So the aerosol goes from this sort of neutral pH to roughly pH 10, maybe a bit over 10.

    DANIELLA: pH is a scale of measurement used to determine how acidic or basic solutions are. So the pH inside the aerosol increases to become more basic when CO2 moves out

    DR. HADDRELL: And it's this really, this increase in pH that really seems to be driving the loss of, um, infectivity of SARS CoV 2 specifically. And what we found is that if you just increase the amount of CO2 in the room, so to say just 800 PPM CO2, less CO2 leaves the droplet. And as a result, the pH doesn't go up quite as high.

    DR. HADDRELL: This really increases the risk of transmission because again, the virus is remaining infectious in the air for longer.

    DANIELLA: This is really fascinating if you think about how this idea pairs with ventilation, which is helpful for bringing in clean air on its own. But also if the ventilation is good, and there’s not a lot of CO2 in the room, the bicarbonate in aerosol we breathe out leaves the aerosol faster and, from what Dr. Haddrell saw in his experiments, SARS–CoV-2 loses its infectiousness faster. That’s pretty cool. 
    A cheap and effective way to tackle viral transmission?  Count me in!

    DANIELLA: Unfortunately, climate change is slowly chipping away at how useful some of these findings are. If the C02 in the air is high outside and inside, then ventilation has less of a powerful effect 

    DR. HADDRELL: And what happens is that if the outdoor CO2 increases, then all of a sudden the, that rate of ventilation is, is lessened.

    DANIELLA: Generally CO2 in the atmosphere is around 440 parts per million or ppm. Now in some cities it’s higher at 500 even 600 ppm because that’s where more CO2 is produced.

    DR. HADDRELL: And so CO2 keeps going up and up and up in the atmosphereThis potential tool, this cheap, easy to use tool, CO2 manipulation. We're losing the use, the ability to use that to effectively limit disease transmission. I'm concerned about that. I think it's, I think it's a, it's a problem.

    DANIELLA:  If you’ll excuse the pun though, the window of opportunity for a clean air revolution is still within reach.

    4. HOW DO WE SOLVE IT?

    DANIELLA: It’s a big question. And it points to bigger structural issues. I definitely don’t have all the answers but there are concrete things we can do to cut disease transmission like cleaning the air we share, wearing respirators, prioritizing community health and rejecting the idea that we have to trade our health so other people can make money.

    If we want to tackle the pandemics we already have and avoid new ones, climate change is one of the main threats to human life as we know it. Ending climate change is ending pandemics is ending systemic racism is ending ableism. These things are connected.

    Climate change and all the things producing it - capitalism, industry, war and bombing - everything that puts mass amounts of carbon into the air - is a driver of disease and poor health, including making it easier for fungi to live in human beings, forcing animals that need a certain climate to have to move. This puts pressure on animal reservoirs of disease to spill over into humans 
    particulate matter from wildfires like we saw in LA is correlated to bad outcomes from COVID, cancers, and long term health problems.  

    Put another way - we can only survive if the planet survives. 
    The various forms of systemic oppression that exist in this world are in direct opposition to a thriving planet. 

    Like Dr. Randall said, we need more cross disciplinary collaboration. Our only saviour is ourselves. And first public health needs to earn trust. 

    DR. RANDALL:  I have friends who know that I did this research and they're, they've asked me explicitly, you know,  can we trust what the CDC says about bird flu? Can we trust what these public health institutions say? Like, is it bad? And when will we know if it gets bad?

    And my honest answer to that is I don't think. That you can trust that you will be told when it is bad. I think that we have really gotten past the part, um, where we can, uh, trust public health institutions to say something that may make a presidential administration look bad or go against an order that they've been given.

     that's such an interesting shift in public health, right? what is the field of public health for, um, and how it's more and more turning towards, um, you know, an individual burden and really antithetical to what public health was established to be, which is that, uh, throughout decades, we have sacrificed a little bit.of autonomy or individualism so that we could have a public health institution. We get vaccinated even if we're afraid of needles, right? We wear a mask even if it's slightly uncomfortable. We do these things because we understand that public health is for a public good, not because we're like, well, we're on our own, every, every woman for herself.

    But that's really what's happened in the wake of COVID, where it's like, if you want to wear a mask, you have to You go ahead. You are free to wear a mask or not and wear one but that has nothing to do with me And it's been really interesting seeing sort of this individualism take over the sort of ethos of public health  

    DANIELLA: I’ve seen it happen. People I went to school with have hit me with the “well it’s a personal choice and I’m okay with my personal risk assessment of COVID and nothing you can say will convince me otherwise” 

    DR KATIE RANDALL:  I would like to depoliticize giving a shit about the health of the people around you so that we can move forward and learn that like,  my, it is my responsibility at least a little bit to care about public health and it's okay for our public health institutions to expect that of me for a larger societal goal.

    That's what I want for my daughter. I want her to be able to exist in a world where  And a society that cares about, um, you know, immunocompromised people and elderly people and disabled people. And I want her to participate in that and understand the value in like, I can do this small thing for the people around me.

    And I can expect that they will do something for me as well. Um, and I think that we have really lost that. And I thought maybe we'd come out of COVID with that. And I think it's actually. done the exact opposite, um, for a lot of people, which is really disheartening. But so that's the world I want. I'm not sure right now, and I think this is where I'm still in the doom and gloom.

    I don't really know how to get there. I think we can. Other societies, other, other countries have. I think we can

    DANIELLA: I think we can too. But we need a plan. There are a lot of pieces but here are some ideas: 

    People need to know about and understand the basics of airborne transmission because COVID and a bunch of other diseases are in our faces right now. I hope this episode helps check off that box. 

    Public health leaders need to clearly and prominently explain to decision makers and the public why and how to use ventilation and air filtration. They also need to ensure clean air in public buildings - especially hospitals and schools - to reduce population level disease transmission. 

    Public health leaders need to provide accurate information about respirators and normalize their use as a preventative tool. Keep an eye out for a future episode on this. High quality respirators should be available for free to everyone.

    We need better rapid tests too so people can use them to know if they’re infectious before they show symptoms. We need better COVID vaccines that work to create long lasting immunity and block infections.

    But the first thing public health leaders could do is take accountability and be honest that in this instance, public health decision makers have made a big mistake about disease transmission. COVID and many other diseases are not spread only by droplets. And they could acknowledge it’s important to course correct on airborne transmission for everyone’s benefit. A mistake doesn’t mean public health is not valuable. In fact, it’s so valuable we need to get past this error and get everyone on board to make it work for everyone and this planet.

    Because there is a hell of a storm brewing.

    DR RANDALL: there is still a place and a role for epidemiology and public health that's really, really important. 

    And so I don't want us to abandon it. I want us to put, to build it up and make it robust and make it, um, something that communicates well and researches well and works across disciplines well so that we can, um, kind of regain, um, um, A certain trust and standing,

    DANIELLA: Maybe there's a version of the Icarus story where he doesn't drown, gets pulled ashore by a group of people who care that someone is stranded and drowning. 
    Maybe they build a few rescue boats together, set up a lifeguard team and swimming lessons for free so nobody drowns…
    We have the answers. Failing an open book test is a choice. 
    The solutions to airborne transmission are in our hands.
    And it’s not handwashing! 
    The best time to act on airborne transmission would have been 5 years ago. 
    The next best time is now!

    I’m Daniella, thank you for listening to Public Health is Dead. 
    Catch you next time!


     

    If you liked this episode, please leave us a review! And if you’d like to hear more of Public Health is Dead, consider chipping in for production costs. This is an indie project that takes a lot of time and energy to produce and it’s made completely out of pocket. Support the show at publichealthisdead.com
     

    CREDITS
    This episode of Public Health is Dead was created, hosted, written, edited, and produced by me - Daniella Barreto 

    Fact checking and production support from Anika S

    Editing support from Kevin Ball, Sophie Kohn, Anika S, and Lauren M

    Mixing and Sound Design by Alexandria Maillot

Daniella Barreto
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