This New York Times article seems to have an important clue about the increased transmissibility of Omicron (I boldfaced the key points):
The buzzing activity Dr. Amaro and her colleagues witnessed offered clues about how viruses survive inside aerosols. The mucins, for example, did not just wander idly around the aerosol. The negatively charged mucins were attracted to the positively charged spike proteins. Charged atoms such as calcium fly around the droplet, exerting powerful forces on molecules they encounter.
Dr. Amaro speculated that the mucins act as a shield. If the virus moves too close to the surface of the aerosol, the mucins push them back in, so that they aren’t exposed to the deadly air.
“What we think is that it’s actually covering itself in these mucins, and that’s acting like a protective coating for it during flight,” Dr. Amaro said.
This discovery may help explain how the Delta variant became so widespread. Delta’s spike proteins have a more positive charge than those on earlier forms of the coronavirus. As a result, mucins huddle more closely around them. That attraction could potentially make the mucins a better shield.
Every now and then, one of the simulated coronaviruses flipped open a spike protein, surprising the scientists. “The Delta variant opens much more easily than the original strain that we had simulated,” Dr. Amaro said.
A simulation of the Delta variant’s spike protein suggests that it opens wider than the original coronavirus strain, which may help explain why Delta spreads more successfully.
Once a coronavirus enters someone’s nose or lungs, the Delta spike’s wide opening may make it better at infecting a cell. But Dr. Amaro suspects that it’s bad for a coronavirus to open a spike protein when it’s still inside an aerosol, perhaps hours away from infecting a new host. “If it opens too soon, it could just fall apart,” Dr. Amaro said.
Some of the molecules that are abundant inside aerosols may be able to lock the spike shut for the journey, she said. Certain lung surfactants can fit into a pocket on the surface of the spike protein, preventing it from swinging open.
To test that idea and explore others, Dr. Amaro and her colleagues are stretching out the time frame of their simulation a hundred times, from ten billionths of a second to a millionth of a second. They’ll also investigate how the acidity inside an aerosol and the humidity of the air around it may change the virus.
Dr. Amaro and her colleagues are making plans to build an Omicron variant next and observe how it behaves in an aerosol. They want to wait for structural biologists to work out the three-dimensional shape of its spike proteins before getting started. But just looking at the early findings about Omicron, Dr. Amaro already sees one important feature: “It is even more positively charged,” she said.
Because Omicron’s spike proteins are even more positively charged than Delta’s, it may build a better mucin shield in aerosols. And that may help make it even more transmissible.
In other words, Delta lasts longer in the air than the original strain (which itself could last in the air for as long as three hours) and Omicron is even hardier. This seems to track pretty well with increased spread in households and across hotel corridors. In the latter example, the prevailing theory seems to be that it passed from one occupant to the other when they were getting their meals. I find it much easier to imagine the increased transmission resulting from a build-up of Omicron in the air, which then seeped through a gap in the door, rather than Omicron having developed sentience and seeking out new hosts during fleeting encounters. Doors to hotel rooms aren’t exactly airtight. Together with the aforementioned 70-fold replication speed in the bronchus, that would tie up the transmissibility question quite nicely—infected people are spewing a lot more virus, which lasts longer in the air. We are all super-spreaders now.
The “air hardiness” also makes the jump from wild mice that much more plausible. With a virus that survives such a long time in the air, it’s a lot easier to imagine zoonosis and reverse zoonosis occurring, without having to get terribly close to an infected animal.
Another corollary of all this would be that you should assume that you’re going to get infected if you live in a multi-family residence with any shared indoor spaces whatsoever. Or consider getting an indoor air purifier, even if you live alone. Scratch that; if you haven’t already gotten an air purifier it’s probably too late.
In other words, Delta lasts longer in the air than the original strain (which itself could last in the air for as long as three hours)
This is tangential, but it’s been fascinating to me to watch the spread of that “three hours” factoid. I believe it originally comes from this paper: https://www.medrxiv.org/content/10.1101/2020.03.09.20033217v1.full.pdf (Note that “HCoV-19” was referring to what is now designated “SARS-CoV-2″, i.e. COVID-19.)
I very gently criticized it at the time for having a quite misleading abstract, regarding the “three hours” figure:
This abstract, as far as I can tell, is where the “three hours” factoid originated, which has now become gospel that appears on public health pages like your link above. In reality, the abstract said they detected the virus in aerosols for “up to three hours” because that was the duration of the experiment. It’s obvious from graphs, as well as their computed half-life figure—which is coincidentally pretty close to three hours—that if they had continued the experiment, they would have kept detecting viable virus for a multiple of that time. (Of course, this figure is also kind of meaningless anyway, since the initial quantity of virus they’re experimenting on was arbitrary! Only the half-life is really meaningful, but that doesn’t make good headlines.)
It feels very weird to me to have “been there at the beginning” for this. I have no specific qualifications for interpreting this paper, beyond being smart and careful. It’s a little depressing (but that’s the COVID story.)
(I would love for someone to correct my story here, and find some other explanation for where this factoid came from, or argue that I’m wrong about it being misleading to the point of error. I really don’t like this story or what it implies.)
This New York Times article seems to have an important clue about the increased transmissibility of Omicron (I boldfaced the key points):
In other words, Delta lasts longer in the air than the original strain (which itself could last in the air for as long as three hours) and Omicron is even hardier. This seems to track pretty well with increased spread in households and across hotel corridors. In the latter example, the prevailing theory seems to be that it passed from one occupant to the other when they were getting their meals. I find it much easier to imagine the increased transmission resulting from a build-up of Omicron in the air, which then seeped through a gap in the door, rather than Omicron having developed sentience and seeking out new hosts during fleeting encounters. Doors to hotel rooms aren’t exactly airtight. Together with the aforementioned 70-fold replication speed in the bronchus, that would tie up the transmissibility question quite nicely—infected people are spewing a lot more virus, which lasts longer in the air. We are all super-spreaders now.
The “air hardiness” also makes the jump from wild mice that much more plausible. With a virus that survives such a long time in the air, it’s a lot easier to imagine zoonosis and reverse zoonosis occurring, without having to get terribly close to an infected animal.
Another corollary of all this would be that you should assume that you’re going to get infected if you live in a multi-family residence with any shared indoor spaces whatsoever. Or consider getting an indoor air purifier, even if you live alone. Scratch that; if you haven’t already gotten an air purifier it’s probably too late.
God help us.
This is tangential, but it’s been fascinating to me to watch the spread of that “three hours” factoid. I believe it originally comes from this paper: https://www.medrxiv.org/content/10.1101/2020.03.09.20033217v1.full.pdf (Note that “HCoV-19” was referring to what is now designated “SARS-CoV-2″, i.e. COVID-19.)
I very gently criticized it at the time for having a quite misleading abstract, regarding the “three hours” figure:
https://twitter.com/gwillen/status/1237854407007457280 https://twitter.com/DrNeeltje/status/1237895661967642626 https://twitter.com/gwillen/status/1237896626355593221
This abstract, as far as I can tell, is where the “three hours” factoid originated, which has now become gospel that appears on public health pages like your link above. In reality, the abstract said they detected the virus in aerosols for “up to three hours” because that was the duration of the experiment. It’s obvious from graphs, as well as their computed half-life figure—which is coincidentally pretty close to three hours—that if they had continued the experiment, they would have kept detecting viable virus for a multiple of that time. (Of course, this figure is also kind of meaningless anyway, since the initial quantity of virus they’re experimenting on was arbitrary! Only the half-life is really meaningful, but that doesn’t make good headlines.)
It feels very weird to me to have “been there at the beginning” for this. I have no specific qualifications for interpreting this paper, beyond being smart and careful. It’s a little depressing (but that’s the COVID story.)
(I would love for someone to correct my story here, and find some other explanation for where this factoid came from, or argue that I’m wrong about it being misleading to the point of error. I really don’t like this story or what it implies.)
So 3 hours was too low even for the original strain??? Jesus, no wonder so many cases are untraceable.
Thanks for some possible details about the relevant ‘gears’!
Gears! I love it!
I picked that term up from Zvi but he himself links to this LW post for background/context:
Gears in understanding—LessWrong
It is a wonderfully useful term/idea to have in the back of your mind!