Opinion | Why Covid's Airborne Transmission Was Acknowledged So Late - The New York Times - 0 views
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A week ago, more than a year after the World Health Organization declared that we face a pandemic, a page on its website titled “Coronavirus Disease (Covid-19): How Is It Transmitted?” got a seemingly small update.
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The revised response still emphasizes transmission in close contact but now says it may be via aerosols — smaller respiratory particles that can float — as well as droplets. It also adds a reason the virus can also be transmitted “in poorly ventilated and/or crowded indoor settings,” saying this is because “aerosols remain suspended in the air or travel farther than 1 meter.”
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on Friday, the Centers for Disease Control and Prevention also updated its guidance on Covid-19, clearly saying that inhalation of these smaller particles is a key way the virus is transmitted, even at close range, and put it on top of its list of how the disease spreads.
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But these latest shifts challenge key infection control assumptions that go back a century, putting a lot of what went wrong last year in context
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If the importance of aerosol transmission had been accepted early, we would have been told from the beginning that it was much safer outdoors, where these small particles disperse more easily, as long as you avoid close, prolonged contact with others.
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We would have tried to make sure indoor spaces were well ventilated, with air filtered as necessary.
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Instead of blanket rules on gatherings, we would have targeted conditions that can produce superspreading events: people in poorly ventilated indoor spaces, especially if engaged over time in activities that increase aerosol production, like shouting and singing
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We would have started using masks more quickly, and we would have paid more attention to their fit, too. And we would have been less obsessed with cleaning surfaces.
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The implications of this were illustrated when I visited New York City in late April — my first trip there in more than a year.
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A giant digital billboard greeted me at Times Square, with the message “Protecting yourself and others from Covid-19. Guidance from the World Health Organization.”
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That billboard neglected the clearest epidemiological pattern of this pandemic: The vast majority of transmission has been indoors, sometimes beyond a range of three or even six feet. The superspreading events that play a major role in driving the pandemic occur overwhelmingly, if not exclusively, indoors.
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The billboard had not a word about ventilation, nothing about opening windows or moving activities outdoors, where transmission has been rare and usually only during prolonged and close contact. (Ireland recently reported 0.1 percent of Covid-19 cases were traced to outdoor transmission.)
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Mary-Louise McLaws, an epidemiologist at the University of New South Wales in Sydney, Australia, and a member of the W.H.O. committees that craft infection prevention and control guidance, wanted all this examined but knew the stakes made it harder to overcome the resistance. She told The Times last year, “If we started revisiting airflow, we would have to be prepared to change a lot of what we do.” She said it was a very good idea, but she added, “It will cause an enormous shudder through the infection control society.”
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In contrast, if the aerosols had been considered a major form of transmission, in addition to distancing and masks, advice would have centered on ventilation and airflow, as well as time spent indoors. Small particles can accumulate in enclosed spaces, since they can remain suspended in the air and travel along air currents. This means that indoors, three or even six feet, while helpful, is not completely protective, especially over time.
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Meanwhile, many countries allowed their indoor workplaces to open but with inadequate aerosol protections. There was no attention to ventilation, installing air filters as necessary or even opening windows when possible, more to having people just distancing three or six feet, sometimes not requiring masks beyond that distance, or spending money on hard plastic barriers, which may be useless at best
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To see this misunderstanding in action, look at what’s still happening throughout the world. In India, where hospitals have run out of supplemental oxygen and people are dying in the streets, money is being spent on fleets of drones to spray anti-coronavirus disinfectant in outdoor spaces. Parks, beaches and outdoor areas keep getting closed around the world. This year and last, organizers canceled outdoor events for the National Cherry Blossom Festival in Washington, D.C. Cambodian customs officials advised spraying disinfectant outside vehicles imported from India. The examples are many.
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clear evidence doesn’t easily overturn tradition or overcome entrenched feelings and egos. John Snow, often credited as the first scientific epidemiologist, showed that a contaminated well was responsible for a 1854 London cholera epidemic by removing the suspected pump’s handle and documenting how the cases plummeted afterward. Many other scientists and officials wouldn’t believe him for 12 years, when the link to a water source showed up again and became harder to deny.
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Along the way to modern public health shaped largely by the fight over germs, a theory of transmission promoted by the influential public health figure Charles Chapin took hold
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Dr. Chapin asserted in the early 1900s that respiratory diseases were most likely spread at close range by people touching bodily fluids or ejecting respiratory droplets, and did not allow for the possibility that such close-range infection could occur by inhaling small floating particles others emitted
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In a contemporary example of this attitude, the initial public health report on the Mount Vernon choir case said that it may have been caused by people “sitting close to one another, sharing snacks and stacking chairs at the end of the practice,” even though almost 90 percent of the people there developed symptoms of Covid-19
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It was in this context in early 2020 that the W.H.O. and the C.D.C. asserted that SARS-CoV-2 was transmitted primarily via these heavier, short-range droplets, and provided guidance accordingly
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Amid the growing evidence, in July, hundreds of scientists signed an open letter urging the public health agencies, especially the W.H.O., to address airborne transmission of the coronavirus.
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Last October, the C.D.C. published updated guidance acknowledging airborne transmission, but as a secondary route under some circumstances, until it acknowledged airborne transmission as crucial on Friday. And the W.H.O. kept inching forward in its public statements, most recently a week ago.
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Linsey Marr, a professor of engineering at Virginia Tech who made important contributions to our understanding of airborne virus transmission before the pandemic, pointed to two key scientific errors — rooted in a lot of history — that explain the resistance, and also opened a fascinating sociological window into how science can get it wrong and why.
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biomechanically, she said, nasal transmission faces obstacles, since nostrils point downward and the physics of particles that large makes it difficult for them to move up the nose. And in lab measurements, people emit far more of the easier-to-inhale aerosols than the droplets, she said, and even the smallest particles can be virus laden, sometimes more so than the larger ones, seemingly because of how and where they are produced in the respiratory tract.
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Second, she said, proximity is conducive to transmission of aerosols as well because aerosols are more concentrated near the person emitting them. In a twist of history, modern scientists have been acting like those who equated stinky air with disease, by equating close contact, a measure of distance, only with the larger droplets, a mechanism of transmission, without examination.
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Since aerosols also infect at close range, measures to prevent droplet transmission — masks and distancing — can help dampen transmission for airborne diseases as well. However, this oversight led medical people to circularly assume that if such measures worked at all, droplets must have played a big role in their transmission.
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Another dynamic we’ve seen is something that is not unheard-of in the history of science: setting a higher standard of proof for theories that challenge conventional wisdom than for those that support it.
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Another key problem is that, understandably, we find it harder to walk things back. It is easier to keep adding exceptions and justifications to a belief than to admit that a challenger has a better explanation.
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The ancients believed that all celestial objects revolved around the earth in circular orbits. When it became clear that the observed behavior of the celestial objects did not fit this assumption, those astronomers produced ever-more-complex charts by adding epicycles — intersecting arcs and circles — to fit the heavens to their beliefs.
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He was also concerned that belief in airborne transmission, which he associated with miasma theories, would make people feel helpless and drop their guard against contact transmission. This was a mistake that would haunt infection control for the next century and more.
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So much of what we have done throughout the pandemic — the excessive hygiene theater and the failure to integrate ventilation and filters into our basic advice — has greatly hampered our response.
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Some of it, like the way we underused or even shut down outdoor space, isn’t that different from the 19th-century Londoners who flushed the source of their foul air into the Thames and made the cholera epidemic worse.
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Righting this ship cannot be a quiet process — updating a web page here, saying the right thing there. The proclamations that we now know are wrong were so persistent and so loud for so long.
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the progress we’ve made might lead to an overhaul in our understanding of many other transmissible respiratory diseases that take a terrible toll around the world each year and could easily cause other pandemics.
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So big proclamations require probably even bigger proclamations to correct, or the information void, unnecessary fears and misinformation will persist, damaging the W.H.O. now and in the future.
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I’ve seen our paper used in India to try to reason through aerosol transmission and the necessary mitigations. I’ve heard of people in India closing their windows after hearing that the virus is airborne, likely because they were not being told how to respond
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The W.H.O. needs to address these fears and concerns, treating it as a matter of profound change, so other public health agencies and governments, as well as ordinary people, can better adjust.
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It needs to begin a campaign proportional to the importance of all this, announcing, “We’ve learned more, and here’s what’s changed, and here’s how we can make sure everyone understands how important this is.” That’s what credible leadership looks like. Otherwise, if a web page is updated in the forest without the requisite fanfare, how will it matter?