Chia C. Wang, Kimberly A. Prather, Josué Sznitman
Jose L. Jimenez, Seema S. Lakdawala, Zeynep Tufekci, Linsey C. Marr
2021 · Science
Mechanisms of airborne transmission The COVID-19 pandemic has highlighted controversies and unknowns about how respiratory pathogens spread between hosts. Traditionally, it was thought that respiratory pathogens spread between people through large droplets produced in coughs and through contact with contaminated surfaces (fomites). However, several respiratory pathogens are known to spread through small respiratory aerosols, which can float and travel in air flows, infecting people who inhale them at short and long distances from the infected person. Wang et al . review recent advances in understanding airborne transmission gained from studying the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections and other respiratory pathogens. The authors suggest that airborne transmission may be the dominant form of transmission for several respiratory pathogens, including SARS-CoV-2, and that further understanding of the mechanisms underlying infection from the airborne route will better inform mitigation measures. —GKA
Metadata: Crossref. Abstracts retain their original authors’ rights.
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> especially those similar to covid-19 - are transmitted by larger droplets, which travel less far. The medical establishment believed that (some may still believe). But it is not true. https://www.science.org/doi/10.1126/science.abd9149
The human body is near 37C / 99F and ambient room temperature is typically kept near 22 C / 70 F. Humans are constantly shedding skin dust, which due to their higher temperature are always floating around rooms. Additionally, people are constantly spreading tiny aerosolized particles from their lungs, even without coughing, simply by talking and breathing. For example: https://www.science.org/doi/10.1126/science.abd9149 "Airborne transmission of respiratory viruses" (2021) Science > "Advances in aerosol measurement techniques, such as aerodynamic and scanning mobility particle sizing, have shown that the majority of exhaled aerosols are smaller than 5 μm, and a large…
fraction are <1 μm for most respiratory activities, including those produced during breathing, talking, and coughing." Such droplets can likely pass through cloth masks with little difficulty, and 6 feet of distance is probably irrelevant. The only thing that prevents transmission and infection between nearby people is containment efforts such as BSL-3/4 laboratory precautions and even there, accidental transmission has been documented. Without highly strict quarantine and isolation protocols, we're really all just swimming in the same petri dish when it comes to respiratory transmission.
Excellent question! The distinction here is between droplets and aerosol transmission. As I understand it, droplets are relatively large chunks of water (or whatever), and aerosols are particles in suspension in a gas. At the beginning of the pandemic, most scientific professionals assumed that COVID-19 was transmitted by droplets; the 6 foot distancing advice comes from that assumption, since droplets don't have much range. (Which is not to say that increasing distance didn't help, but 6' wasn't a magic number.) This article goes into useful depth on our new understanding: https://www.science.org/doi/10.1126/science.abd9149?url_ver=...
> The current climate we're in means that consensus science from 50+ years of research and medical practice around the world is being questioned. (A) In some aspects, 50+ years of accepted medical science was wrong. "Droplet dogma" [1,2] was wrong. Now we know that respiratory viruses spread by airborne aerosols [3]. The epistemological tradition of modern medical science seems to be almost solely based on randomized controlled trials (RCTs). They think everything should be studied and verified the same way that new drugs are studied. We use a lot of physical safety measures, like seat belts and airbags in cars, hard hats in construction sites, etc. because they make…
physical sense, and their protective properties have been measured in engineering laboratory studies. Like using crash test dummies when crash testing cars. Engineering and physical sciences have methods to achieve and test knowledge, that are not an RCT with real people. Now the topical topic is face masks. Engineers know respirator masks can filter over 95% of fine particles, but a sizeable part of the medical science still doesn't believe in face masks, due to lack of decisive studies using an RCT-based setup. (B) But then we also have a surprisingly strong anti-vaccine movement. In this case, the consensus of medical science is correct, and vaccines work. So we have A, where medical science was wrong and a bit stubborn to correct itself. Science as whole was not wrong: Engineers and physicists worked out the details of aerosol spread of the virus and the filtering properties of face masks. And then we have B, a genuine anti-science movement. But what to do? If we didn't question the established dogma as used by the authorities, then we would still believe in the droplet dogma, and we would still think face masks are useless. But if we allow the questioning of the established dogma when the dogma is indeed wrong, the how can the general public know when the old dogmas are questioned for good scientific reasons (A), and when not (B)? [1] https://royalsocietypublishing.org/doi/10.1098/rsfs.2021.004... [2] https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3904176 [3] https://www.science.org/doi/10.1126/science.abd9149
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