Despite the heavy tonnage of news coverage about the novel coronavirus to which we’re all subjected 24/7, there are several aspects of the situation that have not to my knowledge been given adequate attention; and these have serious implications for both our own individual behavior and public policy. This article highlights and explains: That much of the spread of COVID-19 is by people who don’t show symptoms of infection; that this occurs primarily not by coughing or sneezing but by aerosol, that we all produce when we breathe or speak; and that wearing a mask is protective of others as well as oneself.
The novel coronavirus causing the present pandemic is also called SARS-CoV-2. Here I call it simply “the virus,” although there are many other viruses and also many other coronaviruses. The disease the virus causes is called COVID-19, which I also call “the disease.”
The facts about the virus and the pandemic are evolving, and even changing, fairly quickly. What I present here are my own present understandings.
How the virus spreads
Symptoms of COVID-19 may not appear until a person has been infected with the virus – and been contagious – for several or more days. A person in this phase is called “pre-symptomatic.” In some people, the disease may be present with no symptoms at all; these people are “asymptomatic.”
More than half the cases of COVID-19 are spread by people who are either pre- or a-symptomatic. There’s no way for these people to be identified except by testing.
And a major means of contagion is by aerosol (as explained below); hence the importance of masks to protect others, not just yourself.
The disease may be spread by large droplets disseminated by coughs or sneezes, which are said to be able to reach as far as 19 or 26 feet. However, according to the essay cited immediately below, the dominant mode of transmission of the disease is by aerosol.
The essay by Marc Wathelet, an immunologist and virologist, has been posted by Paul Craig Roberts, an assistant Treasury secretary in the Reagan administration, in an article titled, “Coming Out of Lockdown Unprepared,” at https://www.paulcraigroberts.org/2020/04/25/coming-out-of-lockdown-unprepared/ and reposted by Ron Unz at https://www.unz.com/proberts/coming-out-of-lockdown-unprepared/ . Dr. Wathelet’s analysis and conclusions are plausible, and are not reflected adequately, if at all, in the current debates about reopening and about mask-wearing. What they have done for me is to make me avoid as much as possible people who don’t wear a mask in a public setting (like the grocery store), and to keep as much distance as possible between me and other people, especially those not wearing masks, even out of doors.
According to Dr. Wathelet:
2.1 Aerosol transmission of COVID-19: the world must face reality. …
An article [just] published in the scientific journal Environment International has … a very unusual [title] for a scientific article: “the airborne transmission of SARS-CoV-2: the world must face reality” https://tinyurl.com/y7tndf24. The authors … underline the extreme importance of the recognition by national authorities of the reality of aerosol transmission: it is necessary that they put in place adequate control measures to prevent the transmission of COVID-19 by aerosol.
2.2 What is an aerosol? And why is this mode so important?
The internal surface of the lungs, the alveoli where gas exchange takes place, … is moist so that with each breath the exhaled air has microdroplets coming from this surface … . These microdroplets remain suspended in the air, and their existence can be easily verified by blowing on a cold window: the fogging that forms is the result of the condensation of these microdroplets; if you pass your finger over this fogging, drops become visible. Speaking, singing, shouting, coughing, sneezing gradually increases the production of this aerosol, of these microdroplets, independently of the production of droplets which can accompany speech and that accompany sneezing.
These expired microdroplets form a cloud that is normally invisible, unless it is cold enough for the microdroplets to condense into fog. When a person is contagious, these microdroplets are infectious and can remain infectious for a long time (hours), floating in the air and being able to move over long distances, very much greater than the separation distance recommended today. …
One might think that these clouds of infectious particles disperse quickly, but in the absence of turbulence, the fluid mechanics tells us that they do not, and the observation of clouds in the sky confirms to us that if they can deform, the clouds are not quickly diluted in the air by wind but move with the wind (the clouds in the sky being aerosols, too). Likewise the smell of cooking, [of a backyard barbecue] for example, can be perceived over long distances if the observer is downwind. And of course aerosol transmission is much more problematic in confined spaces.
2.3 Asymptomatic transmission involves aerosol transmission.
A study indicates that 79% of cases of COVID-19 transmission are not documented (people who are asymptomatic or whose symptom is so minor that it is not recognized) https://tinyurl.com/tpx4css. A Belgian study indicates that 50% of transmissions are asymptomatic https://tinyurl.com/yc3r3592.
The implication is undeniable: asymptomatic transmission, where, by definition, the contagious individual has no symptoms, and therefore in particular has no runny nose, no sneezing, no cough, and therefore no possibility of producing droplets capable of contaminating a physically close individual or a surface, … can only occur by aerosol!
And since even symptomatic transmission also involves aerosol transmission, it is undeniable that the dominant mode of transmission of COVID-19 is by aerosol.
2.4 The consequences on public health measures of aerosol transmission.
… For specialists in the biology of infectious aerosols, there is no doubt that COVID-19 is transmitted by aerosol: “it is a no-brainer” https://tinyurl.com/w2tt7rx. For Professor Gala, “The distance of 1m50 is rubbish. We know that it is a distance which is absolutely minimal and which does not correspond to anything. Https://tinyurl.com/y7wk52ha.
Social distancing is simply ineffective for viruses that are transmitted by aerosol. Only masks allow a crowd density compatible with an almost normal economic activity.
What kinds of material make the best masks?
Apparently the only practical mask for protecting yourself as fully as possible is the NIOSH-approved N95. But other types of mask provide you with some protection, and are quite effective at minimizing your own “aerosol” emissions, thus protecting others.
A recent article titled, “Tests Measure Homemade Masks’ Efficacy” (by Jo Craven McGinty, The Wall Street Journal, April 25 – 26, 2020), compares the percentage effectiveness of masks made from various materials as follows: Coffee filters (2 layers), 10%; Paper towels (5 layers), 40%; Bed sheets (5 layers), 50%; T-shirt fabric (5 layers), 60%; vacuum bags, 90%; Automotive filters, 95%; Furnace filters, 98%. The article cites David Pui and Qisheng Ou, Center for Filtration Research at the University of Miinesota, and notes the researchers tested only the materials, not masks made of the materials, and didn’t account for poor fitting, breathability and other issues.
Besides these numbers, the article makes these observations:
Simple masks, whether medical or makeshift, prevent wearers from dispersing viruses through coughing, sneezing, talking or breathing.
Respirators, like the N95 masks…do the same but also protect wearers from inhaling viruses once they become airborne. …
…[W]hen viruses are ejected, they’re encapsulated in droplets of mucus or saliva, and almost any face covering will trap those particles.
“Normally, you think about wearing a mask to protect yourself,” said Mike Bell, deputy director of the Division of Healthcare Quality Promotion at the U.S. Centers for Disease Control and Prevention [CDC]. “That’s not what this is about. It’s about not spraying respiratory secretions and spit into the air around you.” …
A 100-micron particle will sink at a rate of about one foot a second, Dr. Pui said, and in very dry conditions, it will evaporate in around seven seconds – so some droplets might settle to the ground before releasing a virus – but particles less than one micron will float indefinitely. (Dr. Pui is director of the Center for filtration Research at the University of Minnesota.)
The new coronavirus measures 0.12 micron. …
The best plan, the experts said, is to don a mask, whatever the material, and prevent the virus from becoming airborne to begin with.
So, any kind of mask is better than none, at least with respect to aerosol transmission. But the so-called “social distancing” of six feet does seem inadequate, at least or especially in the absence of any kind of mask. And where coughing or sneezing is involved, the situation is more serious, as illustrated by the foregoing analysis and in the images below.
* * *
Masks stop the viruses one sheds from reaching other persons. They do this effectively. [See images below.]
Flow field during coughing without mask (whooping cough over one breath):
Flow field during coughing with mouth and nose protection:
Why it’s risky to come out of lockdown anytime soon
The best approach to containing the pandemic would be to test large number of people at random, so as to identify pre- and a-symptomatic people; trace their contacts, and isolate them and those with whom they’ve had contact for an appropriate period.
However, there are nowhere near enough test kits, or testing equipment, to permit such widespread testing. There are vastly inadequate supplies of both the kits/equipment and the materials (swabs, chemical agents, etc.) necessary for effective testing. Meanwhile, the reliability of available tests/kits varies considerably. There are false positives, and false negatives.
Because of the wholly inadequate resources for testing and the vast shortage of N95 masks, coming out of lockdown now would be risky at best. Besides more masks and testing, we need continued “social distancing,” and the recommended 6 feet (or 2 meters) may be inadequate, especially among people who are not wearing masks – to some extent, this is true even outside as well as indoors.
Robert Roth worked as a lawyer in consumer frauds and protection for the attorneys general of New York (1980-1991) and Oregon (1993-2007).