Introduction by Croakey: A group of international researchers is calling for urgent changes in public health policies to reflect “ten streams of evidence” that they say collectively support the hypothesis that COVID-19 is spread primarily by airborne transmission, rather than by larger “droplets” as is still the main advice of the World Health Organization.
The team of researchers from the University of Oxford, University of Colorado, University of California, University of North Carolina and the University of Toronto, led by Oxford Primary Health Care Sciences Professor Trish Greenhalgh, published their report, ‘Ten scientific reasons in support of airborne transmission of SARS-CoV-2’, in The Lancet earlier this month.
It challenges a systematic review led by Oxford Professor Carl Heneghan, Director of the Centre for Evidence-Based Medicine, published in March, that states: “The lack of recoverable viral culture samples of SARS-CoV-2 prevents firm conclusions to be drawn about airborne transmission”.
However the Greenhalgh-led research finds there is “consistent, strong evidence that SARS-CoV-2, the virus that causes COVID-19, spreads by airborne transmission” and that while other routes can contribute, the airborne route is likely to be dominant.
As an article in the BMJ outlined this week, how COVID-19 spreads is one of the most debated questions of the pandemic, with significant implications for infection control practices worldwide, although it also notes that the two theories in play are “not mutually exclusive”.
The Lancet report outlines the implications, saying that if an infectious virus spreads predominantly through large respiratory droplets that fall quickly, the key control measures are reducing direct contact, cleaning surfaces, physical barriers, physical distancing, use of masks within droplet distance, respiratory hygiene, and wearing high-grade protection only for so-called aerosol-generating health-care procedures.
By contrast, it says, airborne transmission means the need for more comprehensive measures to avoid inhalation of infectious aerosols, including ventilation, air filtration, reducing crowding and time spent indoors, use of masks whenever indoors, attention to mask quality and fit, and higher-grade protection for health-care staff and front-line workers.
The research cites long-distance transmission in Australian and New Zealand hotel quarantine, “super spreader” concert and church events, and significant transmission of SARS-CoV-2 by people who are asymptomatic as key parts of the accumulated evidence.
“The public health community should act accordingly and without further delay,” the researchers say, adding that they found no study that had provided strong or consistent evidence to refute the hypothesis of airborne SARS-CoV-2 transmission.
The article was described on Twitter as “compelling” by Victoria’s Chief Health Officer Dr Brett Sutton and cited by Public Health Association of Australia president Dr Tarun Weeramanthri in his call on Australian authorities to “stop dancing around the issue of airborne transmission” and its risks for hotel quarantine and Australia’s pandemic management.
In response, she has published a detailed Twitter thread this week refuting many of the criticisms, which is republished in full below with her permission.
In it she says the researchers are “begging” the World Health Organization “to show scientific leadership at this historical moment, in the face of overwhelming evidence”.
See also this Twitter thread by Greenhalgh’s co-author Jose-Luis Jimenez, University of Colorado Chemistry Professor, summarising the Lancet paper.
He explains why most of the long-distance transmission cases are being identified in the quarantine hotels in Australia and New Zealand: “Because the lack of community cases makes it much more certain that transmission happened there. (Can’t do in US) Plus there is video surveillance etc”.
From Trisha Greenhalgh on Twitter:
Had quite a bit of backlash to our paper, published last week, which set out 10 streams of evidence supporting predominance of AIRBORNE spread of SARS-CoV-2. I respond to some criticisms in this thread.
Criticism 1: “The paper is just opinion, and several authors aren’t even doctors.”
Response: No. It’s well-researched scholarly argument, produced by an interdisciplinary team of 6 professors including 3 docs, 2 aerosol scientists and 1 social scientist.
Criticism 2: “Sure, the virus may be airborne, but this is a minor issue. Droplets are so much bigger and more infectious.”
Response: We disagree. Most infection happens by INHALATION. Every gulp of infected air contains thousands of tiny viral-laden particles.
Criticism 3: “Laboratory studies are artificial and low-quality. Viable SARS-CoV-2 virus has never been isolated from ordinary room air.”
Response: Incorrect. People who make these claims are cherry-picking evidence and misclassifying excellent lab studies as “low-quality”.
Criticism 4: “Half air sampling studies found no virus, therefore the virus is not airborne or airborne is minor route.”
Response: Logical fallacy. If I go for a walk and don’t see a kingfisher, this proves neither that kingfishers don’t exist nor that they’re almost extinct.
Criticism 5: “In contrast to the sparse and flawed studies of aerosols, the virus has been easily and consistently cultured from droplets.”
Response: Incorrect. The only evidence cited to support this claim seems to be “unpublished data from my lab”.
Criticism 6: “This droplet v aerosol argument is just semantics. It doesn’t change the recommendations.”
Response: No it’s not just semantics. “Predominantly airborne” means we need a RADICALLY different approach to prevention policy (next tweet).
Airborne precautions include:
Ventilation. Open windows and doors, encourage draughts.
Air filtration w HEPA filters (+ DISCOURAGE air-recycling air-conditioning).
Ensure masks are high-quality, well-fitting and worn whenever indoors.
Limit time indoors.
Avoid close contact.
Criticism 7: “Airborne infection occurs beyond 2m. The virus spreads mostly via close contact. Therefore close-contact spread isn’t airborne.”
Response: Logical fallacy. MOST airborne spread occurs at CLOSE RANGE (physics innit: particles don’t magically jump the first 2m).
Criticism 8: “Given that anything smaller than 5 microns is a droplet, and droplets fall within 2m, we can largely forget about transmission beyond 2m.”
Response: Incorrect. Particles of up to 100 microns travel far beyond 2m in the air, so physical distancing isn’t enough.
Criticism 9: “The paper is scaremongering. If we say SARS-CoV-2 is spread through the air, people will panic.”
Response: But it IS spread through air, and until we acknowledge that, our measures to control its spread will be ineffective. Lying isn’t an effective strategy.
Criticism 10: “Okay it’s airborne, but it’s not PREDOMINANTLY airborne”.
Response: The evidence suggests that it is. Super-spreader events have no other explanation. Over-dispersion. Long-range infection in quarantine hotels. Many other examples in the paper. Please read it.
Criticism 11: “A systematic review came to the opposite conclusion.”
Response: A review isn’t gold-standard if it a) omitted topic experts, b) asked an overly narrow question, c) misclassified high-quality studies as low-quality, d) failed to account for disconfirming evidence.
Criticism 12: “But systematic reviews are always more rigorous than narrative reviews”.
Response: No they’re not. We scotched that flawed assumption here:
Criticism 13: “The paper is an ad hominem attack against individuals in the WHO.”
Response: Please read the paper. It’s not personal. Thousands are dying daily. We’re begging WHO to show scientific leadership at this historical moment, in the face of overwhelming evidence.
Link to the paper again:
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