Post #745: Aerosol transmission — I had to comment on this one.

Source:  New York Times 7/5/2020.

The upshot of this post is, social distancing is NOT enough.  It’s not enough, due to aerosol (airborne) spread of COVID-19.  If you are indoors with people other than family, wear the best mask you can get, KN95 and N95 included.



Recall the difference between droplets (particles 5 microns and larger) and aerosols (particles under 5 microns).  Droplets rapidly fall out of the air.  Aerosols can float in the air for hours.

“Droplet transmission” of COVID-19 is the reason for the 6′ social distancing rule.  It’s what the CDC keeps nattering about, that the main source of transmission of infection is individuals who cough or sneeze and emit a bunch of droplets containing the virus.  Even though that cannot possibly explain the spread of COVID-19 for the past four months or so (Post #565),because nobody has been dumb enough to be out in public while visibly ill.

But, stay out of sneeze range (6′), said the CDC, and you’re safe.  Social distancing will solve this problem.  Because it’s being transmitted by droplets.

“Droplet transmission” is the reason the CDC originally said that you didn’t need to wear a mask in public.  The story is that if the droplets only go 6′, and you’re maintaining your social distancing, then masks are unnecessary.  You’re out of cough/sneeze range.

But aerosol spread is the reason that outdoors is far safer than indoors.  In crowded indoors settings, aerosols build up, raising infection risk.  Outdoors, space and air currents disperse aerosols to levels that will (typically) not cause infection.  (Droplets, by contrast, don’t care if you are indoors our out — they’ll only go six feet either way.)

Aerosol spread is the reason that singing is so dangerous.  (I have numerous posts on that topic, which you may search for if you wish.)  Singing generates aerosols at the same rate as coughing.  Suffice it to say that the latest twist in that saga is that California has banned singing in church services.  This is long after Germany did that, and after most mainstream denominations did that.

I believe I first started talking about aerosol transmission four months ago, in Post #573, March 6, 2020.   That’s when it became obvious to me that, despite what the CDC was saying, the preponderance of evidence indicated that aerosol transmission of disease was a real and material threat.   That’s about when I shaved my beard and decided to wear a mask whenever I was in public.

And the evidence has only gotten clearer and stronger since that time.  It was obvious at that time that aerosol transmission had to be an important factor.  It’s far more obvious now.   Obvious, even to a mere economist like me, with no medical or formal epidemiological training.  The only explanation of the facts was aerosol transmission of COVID-19.

But the World Health Organization (WHO) and the US CDC absolutely cannot bring themselves to say that aerosol spread of COVID-19 is real and material.  No matter what the evidence. No matter that many important infectious disease (tuberculosis, measles) are know for aerosol spread.  Despite overwhelming evidence of superspreader events that could only have occurred via aerosol transmission of disease.

Thankfully, many US institutions acted (to some degree) as if aerosol spread were real, despite what the CDC says.  (Or, really, what it will not say.)  And certainly, every state that has favored outdoor over indoor settings is implicitly acknowledging the importance of aerosols.  (Because, hey, if it’s all about droplets, they only travel 6′ whether you are indoors or out.)  Even the CDC’s altered guidance implicitly assumes aerosol spread matters (See Post #602).

And the result is that the guidance we get is illogical and inconsistent.  We are doing a lot of things — such as wearing masks in public while social distancing, such as favoring outdoor settings over indoor, such as banning singing at religious services — that tacitly acknowledge that aerosol transmission in the community setting is a real threat.

But the WHO and CDC won’t just flat-out come out and say it.  So there are other things that we all ought to be doing, that we aren’t.  These include wearing masks indoors even if you are properly social distancing.  These including favoring quick and cheap upgrades of commercial ventilation systems to include more circulation, and to use filters with high MERV ratings or to use high-rated 3M Filtrete filters.

And there’s one more thing we should be doing.  I think it’s the reason the CDC ignores aerosol transmission.  Above all, aerosol transmission of COVID-19 means that we should be providing at-risk workers with proper aerosol-stopping masks.  Chinese-made KN95s would be just fine for that.  And those seem to be readily available.  And thanks to another hide-bound Federal bureaucracy — the FDA — those are still frowned upon for use in hospital settings.  So, you might as well feel free to buy one.

I don’t normally just pull something out of the newspaper, quote it, and be done. But I think this bit of reporting summarizes what I’ve been saying all along, about aerosol transmission of COVID-19, and about the established public health authorities’ absolutely unwillingness to recognize that.

Ready:  From this NY Times article, emphasis mine:

But the infection prevention and control committee in particular, experts said, is bound by a rigid and overly medicalized view of scientific evidence, is slow and risk-averse in updating its guidance and allows a few conservative voices to shout down dissent.

“They’ll die defending their view,” said one longstanding W.H.O. consultant, who did not wish to be identified because of her continuing work for the organization. Even its staunchest supporters said the committee should diversify its expertise  and relax its criteria for proof, especially in a fast-moving outbreak.

That sums it up for me.  Hidebound academic outlook, unwillingness to admit error, only talk to a experts with a narrow viewpoint, require impossible-to-meet standards of proof.  That’s what has kept us in this weird never-land where we are taking some — but not all — of the precautions that aerosol transmission should require.

It’s now four months since some untrained blogger — me — was able to put two and two together.  And the WHO and the CDC still can’t deal with it.  When this is all over, I sure hope some heads roll over this.  Barring that, maybe the CDC can finally come to grips with aerosol spread, and can start recommending that we do all the things that implies.