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Opinion | Why Covid’s Air Transmission Was Recognized So Late


Linsey Marr, a professor of engineering at Virginia Tech who made important contributions to our understanding of airborne virus transmission prior to the pandemic, pointed out two major scientific errors that are rooted in history and explain the resistance, and also opened a fascinating sociological window on how science can go wrong and why.

First, said Dr. Marr, the upper limit for particles to float is actually 100 microns, not five microns as is commonly believed. The false claim of five microns may have arisen because previous scientists linked the size at which respiratory particles could reach the lower airways (important for studying tuberculosis) with the size at which they float in the air.

Dr. Marr said when you breathe a particle out of the air, it’s an aerosol. She agreed that droplet transmission is possible through a larger breath particle if, for example, it lands on the eye, but biomechanically, she said, nasal transmission encounters obstacles because the nostrils point down and the physics of such large particles make it difficult for them move your nose up. And in laboratory measurements, people emit far more aerosols, which are easier to inhale than the droplets, and even the smallest particles can be laden with viruses, sometimes even more than the larger ones, apparently because of how and where they are in the Airways produced.

Second, she said, proximity also promotes the transmission of aerosols, as aerosols are more concentrated near the person who is emitting them. In a twist of history, modern scientists have acted like those who equated stinking air with disease by equating close contact, a measure of distance, only to the larger droplets, a transmission mechanism. without examination.

Because aerosols infect even at close range, measures to prevent droplet transmission – masks and distancing – can help dampen transmission, including in airborne diseases. However, this oversight has led medical professionals to assume that droplets must have played a major role in their transmission, if such measures work at all.

Other false assumptions flourished. For example, in July, immediately following the letter from hundreds of scientists questioning the droplet paradigm, Reuters reported that Dr. John Conly, chair of a major WHO infection prevention working group, said there would be many more cases if the virus were in the air, asking, “Wouldn’t we see literally billions of cases worldwide?” He made similar claims last month. And he’s not the only member of this group to claim this, a widespread belief in the world of infection control well into 2021.

Dr. However, Marr pointed out that there are airborne diseases like measles which are highly contagious and others like tuberculosis that are not. While SARS-CoV-2 is certainly not as contagious on average as measles, it can be highly contagious in the widespread events that trigger the pandemic.

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