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Airborne transmission of COVID-19: The controversy

Last week, 239 scientists in 32 countries published an open letter to the WHO arguing that airborne transmission of COVID-19 occurs and urging it to change its recommendations. What is behind this controversy?

One of the biggest mysteries early on in the COVID-19 pandemic that continues to some extent even today is how SARS-CoV-2, the coronavirus that causes COVID-19, spreads. While it’s always been known to spread primarily through respiratory droplets (and that is still thought to be the primary method of spread), there are still so many questions that remain. For instance, you might remember that early on in the pandemic, fomites (objects on which virus-laden respiratory droplets could land and thereby harbor the virus) were thought to be a major source of infection, as people would touch such objects and then touch their face, and no doubt many of you remember all the breathless stories in March about studies showing that SARS-CoV-2 could survive up to three days on plastic and metal surfaces and up to 24 hours on cardboard. Then, a month ago, the CDC published a news release and updated its website to say that indirect contact from a surface contaminated with coronavirus is a potential way to contract COVID-19 but not the most prominent way that the virus infects people, emphasizing that the “primary and most important mode of transmission for COVID-19 is through close contact from person-to-person” and stating that fomite transmission is not “thought to be the main way the virus spreads.” None of this makes it any less of a good idea or any less imperative that you wash your hands frequently and avoid touching your face. The virus can still spread that way; it’s just not the primary driver of infection. The real debate though bubbled up in the news over the 4th of July weekend in the form of a story in The New York Times entitled “239 Experts With 1 Big Claim: The Coronavirus Is Airborne“:

The World Health Organization has long held that the coronavirus is spread primarily by large respiratory droplets that, once expelled by infected people in coughs and sneezes, fall quickly to the floor.

But in an open letter to the W.H.O., 239 scientists in 32 countries have outlined the evidence showing that smaller particles can infect people, and are calling for the agency to revise its recommendations. The researchers plan to publish their letter in a scientific journal next week.

Even in its latest update on the coronavirus, released June 29, the W.H.O. said airborne transmission of the virus is possible only after medical procedures that produce aerosols, or droplets smaller than 5 microns. (A micron is equal to one millionth of a meter.)

Proper ventilation and N95 masks are of concern only in those circumstances, according to the W.H.O. Instead, its infection control guidance, before and during this pandemic, has heavily promoted the importance of handwashing as a primary prevention strategy, even though there is limited evidence for transmission of the virus from surfaces. (The Centers for Disease Control and Prevention now says surfaces are likely to play only a minor role.)

The text of the letter can be found here.

Reading the news stories and the letter, I thought of two things. First, the reaction to this story reminds me of the reaction to stories that have emerged regarding how presymptomatic and asymptomatic COVID-19 patients can spread coronavirus to others. The second—and more relevant—thing was that this debate reminded me of a very similar debate that I wrote about nearly six years ago. At the time, the nation was gripped in fear that the deadly Ebola virus would make its way here from Africa in order to cause outbreaks, and there was a similar question: Could Ebola be spread by air? Because I’ve written about this before, it allows me to expand a bit on the same basic concepts that I discussed in the context of Ebola and discuss them in the context of what we know about COVID-19. I’ll be very straightforward in admitting that I don’t know yet what to believe on this question, but I’ll look at the basic concepts and the evidence.

Airborne transmission: Droplet size matters

Before I discuss evidence, it’s necessary to know what the experts are talking about when they debate whether COVID-19 spread is airborne. Basically, it all boils down to the size of respiratory droplets. To explain the difference, I’m going to go back to an article by an infectious disease expert named Heather Lander that I cited 6 years ago (remember, in this article she was discussing droplets in the context of claims that Ebola could undergo airborne spread, hence the mention of a bloody wash cloth):

Bodily secretions that make it into the air from various orifices (e.g., nose, mouth) are called droplets and are classified based on size and distance traveled. The smaller the droplet, the longer it stays suspended in the air, the farther it travels and the deeper into the respiratory tract it can go upon inhalation by the person sitting down the aisle from you on the airplane. Teeny-tiny droplets (less than 5 microns) are generally referred to as “aerosols” and can be generated by a cough, a sneeze, exhaling, talking, vomiting, diarrhea, passing gas etc. Aerosols can also be generated mechanically by things like flushing a toilet, mopping, or rinsing out a bloody wash cloth. When aerosols are infectious, they transmit disease when they are inhaled by an organism and its [sic] called “aerosol transmission”. When droplets are larger than 10 microns they are called “large-droplets” and if infectious, they transmit disease by inhalation if the organism being infected is close enough to inhale the particles before they settle out of the air. They can also transmit virus if someone gets showered with droplets from, for example, a sneeze, or touching a droplet that is on the surface of an object (fomite) or someone’s skin and it’s called “large-droplet transmission”.

By way of comparison, SARS-CoV-2 is a bit more than 100 nm in diameter, or 0.1 micron.

It’s more complicated than even that, though:

Not all viruses can form infectious aerosols. It depends on where the virus goes in your body and what happens when it gets there. Aerosol infectivity of a virus is determined by how long the virus remains infectious in the air, how deep into the lungs it can travel, and how many virus particles are actually in each droplet compared to how many are required to actually establish an infection. If a viral infection generates aerosols containing 10 virus particles per droplet, but it takes 1000 virus particles per human cell to establish an infection, then those aerosols are not infectious, even though they contain virus. In addition, while airborne, aerosols begin to lose water content by evaporation and virus particles, especially enveloped particles like Ebola, can be affected by other environmental conditions such as humidity, air currents, and sunlight. These particles are also subject to the laws of physics and mechanical forces. A good example of a virus for which these characteristics have been better defined is influenza and this is an excellent article [PDF] that really explains the different kinds of aerosols and how they are transmitted.

If you keep this in mind, then those studies that you’ve no doubt seen in the press trumpeting how researchers have “isolated coronavirus” from respiratory droplets make more sense. Just detecting virus in droplets doesn’t mean that those droplets are infectious. In particular, remember that most such studies use polymerase chain reaction to detect viral nucleic acid sequences, whose presence alone doesn’t necessarily equate to infectivity. Thus, such droplets might be infectious, but it depends upon how many virus particles are in them and how many virus particles are required to get an infection rolling.

Another important thing to remember is that we are dealing with a continuum. The 5-micron cutoff between an “aerosol” droplet that can hang in the air for a long time and a larger droplet that falls out of the air rapidly, to land on nearby objects, is arbitrary. Humans beings, when coughing, sneezing, or speaking, produce a range of droplet sizes, ranging from aerosols to larger droplets. In order to understand the range of possibilities, this article from the CDC is useful [PDF, linked in the above quote]. Basically, by definition, aerosols are suspensions in the air small enough that they remain airborne for prolonged periods of time because of their low settling density. The article reports that for spherical particles of unit density, settling times for a 3-meter fall are 10 seconds for 100 microns, 4 minutes for 20 microns, 17 minutes for 10 microns, and 62 minutes for 5 microns. Particles with a diameter less than 3 microns in essence do not settle. So for a disease to be truly airborne, it has to produce aerosols that hang in the air for a long time, such that prolonged contact (or even any direct contact at all) with the infected individual isn’t necessary for disease transmission. Also affecting this equation is how far these tiny particles can get into the lung. Particles greater than 6 microns tend to be trapped in the upper respiratory tract, while essentially no deposition of particles into the lower respiratory tract occurs for particles greater than 20 microns. To sum it up, a good rule of thumb is that particles in the micron or submicron range are referred to as, and will behave like aerosols; particles greater than 10 to 20 microns are referred to as large droplets, will settle rapidly, and won’t be deposited in the lower respiratory tract.

It’s even more complicated than that:

Whether propelled by sneezing, coughing, talking, splashing, flushing or some other process, aerosols (an over-arching term) include a range of particle sizes. Those droplets larger than 5-10 millionths of a meter (a micron [µm]; about 1/10 the width of a human hair), fall to the ground within seconds or impact on another surface, without evaporating (see Figure). The smaller droplets that remain suspended in the air evaporate very quickly (< 1/10 sec in dry air), leaving behind particles consisting of proteins, salts and other things left after the water is removed, including suspended viruses and bacteria. These leftovers, which may be more like a gel, depending on the humidity, are called droplet nuclei. They can remain airborne for hours and, if unimpeded, travel wherever the wind blows them. Coughs, sneezes and toilet flushes generate both droplets and droplet nuclei. Droplets smaller than 5-10µm almost always dry fast enough to form droplet nuclei without falling to the ground, and it is usual for scientists to refer to these as being in the airborne size range. It is only the droplet nuclei that are capable of riding the air currents through a hospital, shopping centre or office building.

When infectious disease experts say that a virus is “airborne”, they have a very specific meaning. What they are saying is that the virus is capable of aerosol transmission via inhalation, even when the person inhaling the virus is not in close proximity to the source of the aerosol. In other words, if someone with measles (a very highly infectious virus that can be transmitted through the air), coughs up droplets in a room and then leaves the room and then you enter the room, you can breathe in the measles aerosol and will be very likely to contract measles (that is, if you haven’t been vaccinated against measles or had it before). In other words, droplet transmission is not the same thing as airborne transmission. Airborne transmission can occur in places where the infected patient has been, even if it were hours ago, while droplet transmission requires being close to the infected patient.

That is what this debate is about.

Is COVID-19 transmitted by airborne route?

Specific evidence was discussed addressing whether facemasks work to slow the spread of COVID-19; I don’t feel the need to repeat that discussion in detail. The specific meta-analysis also examined the effect of social distancing on the transmission of coronavirus. The meta-analysis found that a physical distance of more than 1 meter was associated with an 82% decrease in the risk of virus transmission, more precisely that the absolute risk of infection from an exposed individual was 12.8% at 1 m and 2.6% at 2 m, while each additional meter of increased distance resulted in a doubling in the change in relative risk. Taken at face value, this evidence tends to suggest that COVID-19 is transmitted through larger droplets that settle rapidly after short distances. However, it doesn’t exclude the possibility of aerosol transmission.

Most of the evidence for aerosol transmission is anecdotal thus far, albeit nonetheless worrying:

Dr. Morawska and others pointed to severalincidents that indicate airborne transmission of the virus, particularly in poorly ventilated and crowded indoor spaces. They said the W.H.O. was making an artificial distinction between tiny aerosols and larger droplets, even though infected people produce both.

“We’ve known since 1946 that coughing and talking generate aerosols,” said Linsey Marr, an expert in airborne transmission of viruses at Virginia Tech.

Scientists have not been able to grow the coronavirus from aerosols in the lab. But that doesn’t mean aerosols are not infective, Dr. Marr said: Most of the samples in those experiments have come from hospital rooms with good air flow that would dilute viral levels.

The incidents cited above included the spread of coronavirus in a choir at choir practice in March:

The full choir consists of 122 singers, but only 61 made it that night, including one who had been fighting cold-like symptoms for a few days.

That person later tested positive for the coronavirus, and within two days of the practice, six more members of the choir had developed a fever. Ultimately, 53 members of the choir became ill with Covid-19, the disease caused by the virus, and two of them died.

The event, which was reported in March by various news organizations, demonstrated how contagious and dangerous the coronavirus is, especially among older populations. The median age for those attending the practice that night was 69.

On the other hand, the story notes that the choir seats were “were packed together, six to 10 inches apart, far closer than the minimum six-foot recommendation by the CDC during the pandemic.” This incident, to me at least, is not compelling anecdotal evidence of airborne spread beyond large respiratory droplets over short distances landing on fomites.

More suggestive of airborne spread is an incident that occurred in a restaurant in Guangzhou, China in January early in the course of the pandemic, in which one diner infected with coronavirus but not yet feeling ill appeared to spread the disease to nine other people in the restaurant. The hypothesis was that the restaurant’s ventilation system blew virus particles around the dining room. However, 73 other diners in the restaurant did not become sick, nor did the eight employees working the floor at the time. Moreover, all of the people who became sick at the restaurant were either at the same table as the infected person or at one of two neighboring tables. Thus, this particular anecdote isn’t very compelling evidence, either, at least not to me.

Still more suggestive anecdotal evidence of airborne spread comes from a German meatpacking plant, where coronavirus infected more than 1,500 workers:

An outbreak of coronavirus that infected more than 1,500 people at a German slaughterhouse may have been spread by “circulating air”.

Experts fear COVID-19 can be spread inside facilities like the Toennies meat plant in Guetersloh because of the systems they use to pump out cool, moist air inside enclosed rooms.

Martin Exner, director of the Institute for Hygiene and Public Health at the University of Bonn, said: “What has not been known so far is that under such conditions circulating air can keep an aerosol moving.

This outbreak is more consistent with airborne spread of coronavirus.

Basically, most of the evidence for airborne spread is either anecdotal or inferred. For example, one recently published review article notes:

While evidence for airborne transmission of COVID-19 is currently incomplete, several hospital-based studies have performed air-sampling for SARS-COV-2, including one published paper (Ong et al. 2020), one early-release paper (Guo et al., 2020) and 5 papers still in pre-print at the time of writing (Chia et al., 2020, Ding et al., 2020, Jiang et al., 2019, Liu et al., 2020, Santarpia et al., 2020). Four of these studies found several positive samples for SARS-CoV-2 genome (RNA) in air using polymerase chain reaction (PCR) testing (Chia et al., 2020, Jiang et al., 2019, Liu et al., 2020, Santarpia et al., 2020), two found very small numbers of positive samples (Ding et al., 2020), and only one (Ong et al., 2020) found no positive air samples. This evidence at least demonstrates a potential risk for airborne transmission of SARS-CoV-2.


A recent mechanistic modelling study showed that short-range airborne transmission dominates exposure during close contact (Chen et al., 2020). Other studies investigating the transport of human-expired microdroplets and airflow patterns between people also provide substantive support for this transmission route (Ai et al., 2019, Li et al., 2007, Liu et al., 2017). Therefore, in light of this body of evidence for these other respiratory viruses; we believe that SARS-CoV-2 should not be treated any differently – with at least the potential for airborne transmission indoors.

The modeling study by Chen et al is interesting in that it found that, even in short range transmission, smaller exhaled droplets are important, with the large droplet route only predominating when the subjects are within 0.2 m while talking or 0.5 m while coughing and that the large droplet route contributes less than 10% of exposure when the droplets are smaller than 50 microns at 0.3 m apart. Of course, this study is a mathematical modeling study and doesn’t have empirical support for its conclusions, but its finding is consistent with both small aerosol droplets being an important mode of transmission and the observation that transmission efficiency drops off rapidly after 1-2 meters.

The authors further note:

Whilst this evidence may be deemed to be incomplete at present, more will arise as the COVID-19 pandemic continues. In contrast, the end-stage pathway to infection of the droplet and contact transmission routes has always been assumed to be via self-inoculation into mucous membranes (of the eyes, nose and mouth). Surprisingly, no direct confirmatory evidence of this phenomenon has been reported, e.g. where there have been: (i) follow-up of fomite or droplet-contaminated fingers of a host, self-inoculated to the mucous membranes to cause infection, through the related disease incubation period, to the development of disease, and (ii) followed by diagnostic sampling, detection, sequencing and phylogenetic analysis of that pathogen genome to then match the sample pathogen sequence back to that in the original fomite or droplet. It is scientifically incongruous that the level of evidence required to demonstrate airborne transmission is so much higher than for these other transmission modes (Morawska et al., 2020).

They do have a point. It’s been accepted that fomites and self-inoculation are a means of spreading coronavirus, but the evidence has been mostly circumstantial and not that rigorous. The one recent study in the Proceedings of the National Academy of Science (PNAS) that found masks are very effective in slowing the spread of COVID-19 has been cited as indicating that the predominant mode of spread of COVID-19 is airborne was riddled with methodological shortcomings, so much so that dozens of scientists petitioned the journal to retract it, saying the study has “egregious errors” and contains numerous “verifiably false” statements, so much so that a scientist named James Heathers wrote an article for Retraction Watch about it (and one other paper) entitled I agree with your conclusions completely, and your paper is still terrible. (That about sums it up.) Part of the problem is a good thing for you to know, namely that PNAS has a special track, called the “contributed” track, by which members of the National Academies of Science (NAS) can solicit their own peer reviews and submit them with the manuscript. That’s why PNAS has long been known as a dumping ground for NAS members to publish their cast-offs or to publish in areas outside their area of expertise. It’s how, for instance, Linus Pauling got some of his terrible papers claiming that vitamin C is an effective treatment for cancer published. More recently, PNAS has switched to a more standard peer-reviewed model of publishing, but the contributed track still remains for NAS members.

The bottom line

The question of whether COVID-19 can spread by aerosol remains without a definitive answer; however, it could be that the debate has been framed in a way that isn’t helpful. Again, respiratory droplets exist on a continuum, from tiny droplets and droplet nuclei that can travel far and hang in the air a long time to larger droplets that float to earth within seconds to minutes. They can also contain varying numbers of infectious virus particles. As one scientist put it:

People generally “think and talk about airborne transmission profoundly stupidly,” said Bill Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health.

“We have this notion that airborne transmission means droplets hanging in the air capable of infecting you many hours later, drifting down streets, through letter boxes and finding their way into homes everywhere,” Dr. Hanage said.

Experts all agree that the coronavirus does not behave that way. Dr. Marr and others said the coronavirus seemed to be most infectious when people were in prolonged contact at close range, especially indoors, and even more so in superspreader events — exactly what scientists would expect from aerosol transmission.

Dan Diekema, an infectious disease specialist in Iowa, concurs, referring to the controversy as a “tiresome spat“:

As we’ve outlined here and here, a major problem plaguing this discussion is the false dichotomy between “droplet” and “airborne” transmission that we use in healthcare settings (for simplicity of messaging, and because it has served us well for several decades—for reasons I’ll get back to later). This dichotomy divides application of transmission-based precautions between those pathogens spread via respiratory droplets, all of which must absolutely fall to the ground within 6 feet of the source, and those pathogens which become airborne, meaning they travel long distances on air currents, remain in the air for very long periods of time, and most importantly, can cause infection after their airborne sojourns if they find the right mucosal surface.

But we know (and WHO experts know) that there is no such dichotomy—it’s more of a continuum. At the very least there is a middle category, let’s call it Small Particle Aerosol Transmission (or SPAT). Many respiratory viruses (not just SARS-CoV-2) can remain suspended in aerosols and travel distances > 6 feet. As Jorge outlined, it’s probable that transmission events occur when these aerosols are concentrated in closed, poorly ventilated spaces or in very large amounts (e.g. a 2+ hour choir practice, a 3 hour indoor birthday party, a crowded bar). This may explain the superspreading events that drive a lot of SARS-CoV-2 transmission.

The Center for Evidence-based Medicine (CEBM) published a recent review on the evidence base supporting the two-meter rule of social distancing to reduce COVID-19 transmission. In it the authors also discussed the evidence that COVID-19 is transmitted by air and concluded, among other things, that the “longstanding dichotomy of large droplet versus small airborne droplet transmission is outdated and SARS-CoV-2 may be present and stable in a range of droplet sizes, which will travel across a range of distances, including some beyond 2 metres” and that “single thresholds for social distancing, such as the current 2-metre rule, over-simplify what is a complex transmission risk that is multifactorial,” adding that “social distancing is not a magic bullet to eliminate risk,” while further recommending that a “graded approach to physical distancing that reflects the individual setting, the indoor space and air condition, and other protective factors may be the best approach to reduce risk.”

It turns out that, three days ago, the WHO updated its website regarding how COVID-19 is transmitted. In essence, it didn’t change its position that much. It conceded that airborne transmission outside of situations that generate a lot of droplets (such as intubation of COVID-19 patients) could be occurring, while pointing out that the extent to which it is happening is unclear, concluding:

Airborne transmission of the virus can occur in health care settings where specific medical procedures, called aerosol generating procedures, generate very small droplets called aerosols. Some outbreak reports related to indoor crowded spaces have suggested the possibility of aerosol transmission, combined with droplet transmission, for example, during choir practice, in restaurants or in fitness classes.


Urgent high-quality research is needed to elucidate the relative importance of different transmission routes; the role of airborne transmission in the absence of aerosol generating procedures; the dose of virus required for transmission to occur; the settings and risk factors for superspreading events; and the extent of asymptomatic and pre-symptomatic transmission.

Again, my speculation (which will evolve as more evidence comes in) is that aerosol transmission likely can happen but is probably a lot less efficient than spread by larger droplets, which is why there are relatively anecdotes strongly suggesting airborne transmission. What’s really needed is more science. The amount of science, both excellent, terrible, and every level of quality in between, that’s been produced since the pandemic began is truly amazing, but it’s only been less than seven months since the pandemic started in China. As Kimberly Prather and co-authors argue, what’s needed is this:

Aerosol transmission of viruses must be acknowledged as a key factor leading to the spread of infectious respiratory diseases. Evidence suggests that SARS-CoV-2 is silently spreading in aerosols exhaled by highly contagious infected individuals with no symptoms. Owing to their smaller size, aerosols may lead to higher severity of COVID-19 because virus-containing aerosols penetrate more deeply into the lungs (10). It is essential that control measures be introduced to reduce aerosol transmission. A multidisciplinary approach is needed to address a wide range of factors that lead to the production and airborne transmission of respiratory viruses, including the minimum virus titer required to cause COVID-19; viral load emitted as a function of droplet size before, during, and after infection; viability of the virus indoors and outdoors; mechanisms of transmission; airborne concentrations; and spatial patterns. More studies of the filtering efficiency of different types of masks are also needed. COVID-19 has inspired research that is already leading to a better understanding of the importance of airborne transmission of respiratory disease.

The information gathered on these characteristics of SARS-CoV-2, how it spreads, and how it causes disease will then be of use in the study of other respiratory viruses and future pandemics. In the meantime, I’m coming to the conclusion that we should assume that respiratory aerosol is a major mode of spread of COVID-19 and act accordingly. In many ways, we are already doing that, as social distancing and masks are primary means of preventing the transmission of viruses transmitted this way. However, more can be done, particularly in buildings. Additional strategies to mitigate the spread of COVID-19 in buildings could include refreshing stale indoor air, passing recirculated air through a high-efficiency filter to prevent infecting people in adjacent rooms, and other means of keeping airborne virus confined to limited areas. Then, as the science comes in, recommendations can be fine-tuned based on what we learn. In the meantime, there is no reason to be any more alarmed or even, in most cases, to change what we’re doing to protect ourselves and others.

By Orac

Orac is the nom de blog of a humble surgeon/scientist who has an ego just big enough to delude himself that someone, somewhere might actually give a rodent's posterior about his copious verbal meanderings, but just barely small enough to admit to himself that few probably will. That surgeon is otherwise known as David Gorski.

That this particular surgeon has chosen his nom de blog based on a rather cranky and arrogant computer shaped like a clear box of blinking lights that he originally encountered when he became a fan of a 35 year old British SF television show whose special effects were renowned for their BBC/Doctor Who-style low budget look, but whose stories nonetheless resulted in some of the best, most innovative science fiction ever televised, should tell you nearly all that you need to know about Orac. (That, and the length of the preceding sentence.)

DISCLAIMER:: The various written meanderings here are the opinions of Orac and Orac alone, written on his own time. They should never be construed as representing the opinions of any other person or entity, especially Orac's cancer center, department of surgery, medical school, or university. Also note that Orac is nonpartisan; he is more than willing to criticize the statements of anyone, regardless of of political leanings, if that anyone advocates pseudoscience or quackery. Finally, medical commentary is not to be construed in any way as medical advice.

To contact Orac: [email protected]

56 replies on “Airborne transmission of COVID-19: The controversy”

Orac writes,

Then, as the science comes in, recommendations can be fine-tuned based on what we learn.

Hint from MJD,

Present a mouth/nasal spray that affects the hydrophilic/lipophilic balance (ie., HLB) of saliva, and nasal discharge, as a means to inhibit the stability of viruses in expelled body fluids. In simplification, make it difficult for viruses to agglomerate and suspend in the moisture we share through breathing, coughing, and sneezing.

@ Denice Walter,

When you have a cold, such a mouth/nasal spray would make your bad breath much better!

Why is this question so hard to answer? Take a couple ‘organisms’ in cages separated across a room without airflow and piss the infected one off (as one does)* — get it shouting. If the other one gets, then there you go for the win.

*show it clips of Ann Coulter or Tucker Carlson on a repeating loop.

@ Tims July 13, 2020
*show it clips of Ann Coulter or Tucker Carlson on a repeating loop.

You would never get ethics approval.

Because we have collectively decided that we are better than Joseph Mengele and his ilk. If you want to count yourself ethically along with him and the other Nazi doctors, since it seems you think very much as they had, that’s on you.

Whoa… I don’t want to be that guy. Besides, it has the potential to make a bunch of frothing right wing ‘organisms’. There is a better way:

% Americans wearing masks in public places 74. UK 36% We have more selfish covidiots than you. Disappointing as I thought we were a relatively caring society.

Where were they doing the counting? People walking around my neighborhood rarely wear masks. Some have them around their necks and pull them up if other people approach—does that count? Another oddity are women I see walking with their male companion, the woman wearing a mask, the man with no mask at all—not even around their neck. Far fewer than 20 percent are wearing masks. It’s the same thing walking in the business district, except that more people have chin-masks, which they pull over their faces when they have to go into a business. This is crunchy, coastal California, and cases numbers are rising, so I don’t understand the non-compliance.

People walking around my neighborhood rarely wear masks. Some have them around their necks and pull them up if other people approach—does that count?

Sure, if they are outside (I think). What I’ve noticed here (and everybody masked at the beer store lasted about 1 day even though the whole entrance is plastered with mask requirements) is that the employees only keep them on around customers. Troubling, given this airborne question.

That’s exactly what I’m seeing. The chinmasking, the quick pull-up when someone gets close. The masked woman and the unnmasked man walking together. It’s absolutely boggling. The chinmasking gives you plenty of opportunity to leave a little aerosol lingering around, it gives you lots of opportunities to get your hands contaminated, it means you touch your face a lot, and it means you’ve probably got a lousy seal even when you do have it on.

And yeah, I’m in the Bay Area.

I’m having to get better at confrontation. I confronted a guy at the store yesterday who didn’t have a mask on; at least he was shamefaced about it and pulled his shirt up over his face. (That’s another one I’m seeing a lot. A guy – always a guy – walks into a store and just pulls his shirt up over his nose.)

Of the people who are wearing masks in stores and coffeeshops and the like, maybe half have them actually covering their nose.

@ Roadsterguy:

Maybe they’ll wake when they learn that a new study by Monica Gandhi (UCSF) shows that masks protect the wearer too ( via CBS LA) because it cuts down how many virus can get through.

@Denice – I’d love to believe that, but I think there’s a strong macho component going around with compliance around mask wearing and social distancing.

I’ve seen toxic masculinity get in the way of some very basic Good Health. Helmets on bicycles? Really, that’s Not Manly? Hell, helmets on motorcycles. Eating vegetables. Etc.

I would point out that this is something that can change relatively quickly as the pandemic carries on and more people get infected. The virus could quite easily evolve to be better at aerosol infection. There’s direct selective pressure for this to occur. What’s true now may be wrong in a few months, or the anecdotes from earlier in the disease may already not be completely representative. Viruses aren’t static things and it just jumped species.

Just curious. How do you feel about schools opening up? The county school board in Orange County CA where I teach, is recommending a schools open up with zero distancing or PPE. Most of our staff is over 50, many with health problems.

I would be worried because :
1. Orange County’s numbers have not been great
2. real problems with social distancing with younger students
3. age of staff/ health conditions
4. it’s kind of late for planning, no?

NJ’s governor is currently tackling how to re-open schools when the state’s numbers are decreasing and so far, it looks like a staggered schedule will happen ( alternate days i-person/ partially remote see @gov murphy)
A while back, news reported that Germany IIRC would allow older students in person and another country would allow the younger ones who needed in-person education more. It would be enlightening to know how those plans go.

HOWEVER, I just flew in a plane and can report that I wasn’t totally terrified for 5 hours each way because I felt that the airline used SB measures- hepa filters, air filtration increases, distanced seats , masks, hand sanitisers, other cleaning between flights, reduced services/ packaged foods, boarding changes,,alerts if plane was 70% capacity ( free cancellation/ exchanges) attendants/ pilots wore spiffy masks. ( see united hub/ covid 19). It would be interesting to see data about results.


I flew recently as well and agree with your assessment as far as the planes, BUT…the airport itself left much to be desired. A sign at the entrance doors clearly REQUIRED face covering, but many inside were not complying. I complained to the TSA guys and was flippantly told that it was a “Port Authority problem”, not theirs. I asked if there was someone I could talk to and was told I could call them. I asked for a phone number and was told to “google it”. The other problem was the bathrooms–very crowded and no way to distance. There seemed to be no planning or control of this airport other than the food outlets not being open. The attitude of the TSA staff was beyond insulting. The airport in question was Portland, OR.

@ brainmatterz:

The airports were extremely good as well- even TSA- one of the reasons I probably felt safe was because the first flight was very early – the place was empty, no lines, no waits, people wore masks- and the flight back was on 4 July and even more deserted; flights being 15-20% and 10% occupied respectively. Most restaurants/ shops closed in airports, very few people walking about, empty parking lots
It was a once-in-a lifetime experience.


A lot of the problems you mention at the airport are how international airports are organized and regulated(I work at one ). The various authorities are extremely delineated. Hence TSA will not care a whit about the actual airline counters etc. The various departments are very compartmentalised and care not a bit about things out of their jurisdictions. However, do not close the line into THEIR authority,,,,,,,

As an example: YTZ is a busy commuter airport, not handling any commercial size jets. In spite of a newly completed terminal expansion, during very high demand times/emergencies, all gates are occasionally full and we need to off-load a plane the old way- by stairs to buses that take passengers to the gate. The new layout for this needed line marking etc. When we tested it for initial fit we had over FIFTY people there to ensure all the regulations and such were dealt with. Before COVID shutdowns, it was going to be finished last month after 15 months of discussion/planning etc……. all to designate a parking spot, paint out lines for the bus to follow and develop a procedure not one bit of construction needed!

The county school board in Orange County CA where I teach, is recommending a schools open up with zero distancing or PPE.

It’s interesting to see that response in conservative Orange County considering that neighboring LA County schools will have remote-only instruction this fall. Perhaps Mitch McConnell is right that “some people in the country tried to politicize” our nation’s response to the pandemic. . . .

But the worry here is that Trump appears to be taking a post-sharpie approach to the scientists and public health experts who are skeptical of his approach. In the earlier instance, in which Trump doctored a hurricane forecast map with a magic marker, science agencies were forced to undercut their own staff under the threat of job losses. The intense pressure put upon the CDC in response to its school advice seems similar. Other recent reports indicated that White House staff leaked a collection of criticisms against infectious disease expert Dr. Anthony Fauci, based on statements he made early in the pandemic when our knowledge was less certain. Fauci has also had trouble getting approval for media appearances, possibly because of his past history of contradicting the administration’s sunny outlook on the pandemic.

In other words, indications are that the administration is no longer content to push its policy over the contrary advice from scientific and medical experts. Instead, it may be shifting toward silencing and undercutting those experts in an attempt to smooth the acceptance of its policies.

It’s nice to see Fomites mentioned. They seem to have largely disappeared in the teaching of Infection Control (at least on this side of the Pond).

That’s interesting. When I was learning specific-pathogen-free animal work about 10 years ago fomites were the big thing to be worried about. So much so that one facility that was forever having trouble keeping things “clean” refused to allow any non-plastic wrapped paper into the facility. Either you laminated it, or you had to fax it in.

Literally on a fax machine. That was also the place that expected everyone to shower in Dial Gold soap. I was so glad I only had to go in once or twice.

I used to ask newly qualified nurses two questions;
1: When was the last time you emptied a bedpan and;
2: What’s a Fomite?

The answers were never encouraging.

It does depend on the virus. HIV? Not really worth worrying about. Parvo? Months and months of contamination.

“The minimum dose of SARS-CoV-2 that leads to infection is unknown”


blockquote>how many virus particles are actually in each droplet compared to how many are required to actually establish an infection. If a viral infection generates aerosols containing 10 virus particles per droplet, but it takes 1000 virus particles per human cell to establish an infection, then those aerosols are not infectious, even though they contain virus.



How does this actually work? Is it like fertility where it only takes one but it is unlikely that any particular one will make it in or some rapid localized immune response?

But, what about that ‘V-word’ if it came to DIY immunization? As I’ve noted before, it has been stated that mearly getting it in the eyes results in pink eye-like symptoms (I doubt that). But, nerves have ACE2? It can travel along the nerves to other places that have ACE2?

I ‘thought’ the damage throughout the body including brain, heart, and kidneys, (even ‘covid toes’) was due to the wierd coaguopathy and blood clots thrown off from the lungs and general low SpO2 in the first place; But maybe not?

If it was, though, getting it in the eyes could be protective? Eww. Too close to the brain. But what about getting it somewhere with ACE2 that is far from the lungs (the only place where the cytokine storm seems relevent for the disease state) and brain? Like — Urethral sounding??? (god forbid). But, I note that the CDC guidelines do not seem to indicate that the baby batter spreads it even though the balls are where the pee is stored and contain ACE2.

I had another thought. What about an external petri dish with cultured cells with lots of ACE2 that is plugged in like an circulating IV? Get antibody reaction, Less direct contact with nerve cells.

I know my views are crazy, but I’ve never courted un-crazy popularity.

/s (not really)

ok, but the plugin petri dish is the Moderna process (I just love new tech) with all the cells already having the ‘kill me’ placards sticking out… If recipients start having high fevers, seizures, brain fog, or getting artistic, then just unplug it.

Scalability probably sux. foresee underground clinics, I do.

Orac, I think this clause is missing an important word: “which is why there are relatively anecdotes strongly suggesting airborne transmission”

Recommendations based off of assuming airborne transmission should have been implemented in the first place & could have been scaled back if evidence showed to the contrary.

Now people have distancing fatigue & will reject stricter measures.

Please, share your wisdom of how you would have done things differently, being sure to account for the refusal of the current administration to coordinate the distribution of PPE based on need. And be extra sure to explain how you would have gotten your antivax cohort to accept vaccination once a vaccine is available, as that’s a basic principle of airborne transmission prevention.

“Immunize susceptible persons as soon as possible following unprotected contact with vaccine-preventable infections (e.g., measles, varicella or smallpox).”

But Terrie,
what does the CDC know?

Although Hospi Medica 9 July 2020, vaccination with Trivalent Flu vaccine is associated with less risk of severe Covid
and speculation MMR may be associated with less risk of Covid ( e.g. rates of Covid in sailors were lower than expected; service members get MMR/ older people did NOT. It may be the Rubella part)


At any rate,
where is Joel, PhD, MPH ?

@ Terrie,

Why would any administration have been coordinating PPE back in February when Fauci, WHO & CDC were saying COVID-19 wasn’t going to be a big deal in the US?

Why couldn’t public health authorities used their supposed knowledge to start recommending face coverings; even cloth, bandannas, gaiters, etc back in February? Anything that can prevent you from being able to blow out a candle could have mitigated viral spread.

But they didn’t do anything. They waited for permission from the talking heads, blaming “the administration “ for their own failure.

And how, in good conscience, could I ever support a vaccine after a vaccine killed my child? Why would administering a substance that stimulates cytokines, during a pandemic with a virus that kills by inducing a cytokine storm, be something I would advocate for?

@CK, You’re the one who said we should have been pushing airborne transmission prevention from the start. Standard protocol for that includes vaccines where available.

@Denice and F68.10,

It had occurred to me that Joel’s comments had grown increasingly acrid in the last month and a half, so I was thinking of suggesting that he and F68.10 give it a break for a week or so.

Their discussion had devolved to long “you said, I said” posts that mostly ignored or dismissed the other’s point of view.

But I also miss his depth of experience and the wealth of information he brings to our discussions.

FWIW, I still haven’t really started reading Sompayrac. But, since I’ve been listing to a lot of TWiV lately, it will probably make a lot more sense when I do get into it.

@Christine Kincaid Your child died after you cut the oxygen supply. This should be obvious to everybody.
COVID 19 situation is worse now than in February. And Fauci does not know everything. It is people like you who belive that they do.

@ squirrelite

“It had occurred to me that Joel’s comments had grown increasingly acrid in the last month and a half, so I was thinking of suggesting that he and F68.10 give it a break for a week or so.”

Mostly what I am doing. I just hope he will be back.

“Their discussion had devolved to long “you said, I said” posts that mostly ignored or dismissed the other’s point of view.”

I would dispute that, but, well, I’d better drop it.

“But I also miss his depth of experience and the wealth of information he brings to our discussions.”

Me too. He does complain at times that people do not read what he posts… but at times, when I find some time for leisure, I do read them. Still got his eugenicism documentary to go through, though (not a big fan of that gleeful topic).


I probably over-simplified my description.

My perception was that the long back-and-forth reviews had reached the point where I didn’t have time to dig through them trying to figure who had said what to whom and whether I agreed or disagreed.

Part of that was just my current work schedule, which reduced my reading time.

I definitely sympathize with your experience with the French psychiatric system.

@ squirrelelite

“I probably over-simplified my description.”

No offense taken. I assure you.

“I definitely sympathize with your experience with the French psychiatric system.”

Please do not. Reality is always more complex than what can be conveyed by comments on a blog. I’d advise withholding sympathy and also take into account that I do not shy away from exaggerations and strong language to get my point across. So withholding judgement is probably the best option from where you stand.

Are these monkies mimicking sound public health policy?? (just the bookends; idk what the middle part is but I think machine translated had a stroke):

Here is one showing disdain for Dead Leader:

Re the photograph up top, I’m pleased to have discovered that someone at the University of Washington has scanned Milton Van Dyke’s An Album of Fluid Motion (PDF, 177 pp.), which I had as a supplementary text as an undergrad. (After all these years, I’m still amazed that the primary text was the Dover reprint of Horace Lamb’s Hydrodynamics. Geophysics had its own building for a reason, I take it.)

yes no doubt … out the nose or mouth …if u got it & no mask u are spreading it …this looks like how it happens world wide lets fix it now …cheers…happy bob from oz . …8

I did a little search that confirmed my suspicions about who exactly is quite opposed to Dr Fauci:
if you google/ bing his name for recent stories, you’ll find that Trump’s inner circle have been trying to cast doubt upon his efficacy, also I find that Tucker Carlson is not a supporter ( for months).
My own tracking has shown that Del Bigtree and Gary Null have no respect for his expertise ( as if they have the knowledge to judge anything SB)
AND Orac’s scoffers see him as part of the problem not a reliable source for information about Covid.
That’s an interesting group- what do they have in common? Conservative politics and anti-vax sentiment ( either or both)?

@ Denice,

So you believe that Fauci is supported by those with a provax agenda & antivaxxers don’t support him?

I actually do not agree. I personally know people who are provax & very well educated who are completely disgusted with him. And the overload of antivaxxers posting his pre-April statements on social media makes me want to puke.

My own tracking has shown that Del Bigtree and Gary Null have no respect for his expertise ( as if they have the knowledge to judge anything SB)

The one I find most hilarious is Peter “Fauci has been wrong about everything I have interacted with him on” Navarro, who apparently is mightily asshurt about the HCQ debacle.

@ Aarno,

"@Christine Kincaid Your child died after you cut the oxygen supply. This should be obvious to everybody."

I hope you did not mean that the way it sounded & I don’t think you did. To clarify; my twins’ pediatrician appointment was in the morning. They were both vaccinated & the doctor ordered a pulse ox study for her (not her twin, he had been the smallest & most fragile of the two) that was done at home, that afternoon. She passed the study & the respiratory therapists took all her oxygen supply & equipment. By about 5 pm she was wailing that awful, high pitched cry & arching her back. The pediatrician’s after hours triage service was called. The on call doctor said it was “a normal” reaction to the vaccine. Couldn’t get her comfortable until about 2 am & then … she died in her sleep before the sun rose.

Symptoms of encephalopathy should not be “normal”.

"COVID 19 situation is worse now than in February. And Fauci does not know everything. It is people like you who belive that they do."

I believe that Fauci knew the same as I did, back in January that we were in imminent danger from COVID. However, he obviously declined to sound the alarm when he was in a position to do so & I was not. That makes him worse than just being ignorant. He wasn’t ignorant; he was negligent.

I believe that Fauci knew the same as I did, back in January that we were in imminent danger from COVID.

You believe lots of things, but your record of proving any of them is worse than the Cubs in the World Series.

You previously mentioned cutting the oxygen supply, prematurity and a severe infection. You said, too, that you connect the dots only later. So you yourself thought at first that these things caused the death.
Interesting thing is your spoke about normal vaccine reaction. Perhaps this is an actual fact. The death was very fast, too. Certainly a doctor (or a nurse) would recognise an anaphylactic shock

Irony meter explosion of the day, thanks to James (SCIENCE!) Lyons-Weiler’s latest anti-CDC/Fauci diatribe:

“ONE OF THE MOST FRUSTRATING ASPECTS of how academic science conducts itself in the US is high reliance to SELECTIVE ATTENTION to information that suits one’s particular viewpoint in science…To seek only confirming instances that match one’s own viewpoint is positivistic – and it is the essential driver of confirmation bias.”

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