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One possible analysis of recent data would suggest that there is an end in sight (cannot be soon enough) and that perhaps that will happen even before we have a useful vaccine against COVID-19.
#COVID19
1/xοΏΌ
One possible analysis of recent data would suggest that there is an end in sight (cannot be soon enough) and that perhaps that will happen even before we have a useful vaccine against COVID-19.
#COVID19
1/xοΏΌ
This thread and hypotheses are prompted by a conversation between physicians interested in understanding the current pandemic (below). Why do I think there will be a "natural" end?
(this thread my take only)
@VincentRK @vmontori
#COVID19
2/x
(this thread my take only)
@VincentRK @vmontori
#COVID19
2/x
@VincentRK & I were always puzzled at what happened in Wuhan. The stories were tragic and the control measures extreme. Hubei is a province of 58 million people & Wuhan is a city of 11 MοΏΌ. However, the number of cases was only a very small fraction of the population
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Despite, the uncertainty about data and despite the welding of doors to contain the spread, how good can your measures be? Can a population control strategy really be that effective? (we know there are concerns with the data, but the same happened in Italy)
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In this thread @VincentRK shows how the pandemic seems to locally "burn out." The difference between US regions likely reflects a different point of evolution of the pandemic.
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5/x https://twitter.com/VincentRK/status/1276159410264576000?s=20
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5/x https://twitter.com/VincentRK/status/1276159410264576000?s=20
So let's start by looking at the usual epidemiological models are based on the knowledge of three status for any individual: SIR:
S - for susceptible,
I - for infected, and
R - for recovered.
https://images.app.goo.gl/5JjHooBLafeCmMz57
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S - for susceptible,
I - for infected, and
R - for recovered.
https://images.app.goo.gl/5JjHooBLafeCmMz57
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A ubiquitous assumption made is, that at the start, all in the population are susceptible if exposed to a new virus such as SAR-CoV-2. But is this assumption always correct?
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As a pandemic evolves, the susceptible are consider to be those that remain after one excludes those infected and recovered. It is difficult to precisely determine at a given time who is infected because of the dynamic nature of the disease.
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So people assume how many remain susceptible can be estimated by subtracting those with positive antibodies (serology) from the total. Is this consistent with what is being observed?
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Most serologic assays have ranged from 1-3% all the way up to 20-30% in areas such as New York City. And the curve seems to be ending in NYC. What gives?
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Similarly, in a recent study of an isolated Alpine community in Austria shows that even in a close-knit community only a fraction of people became infected.
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11/x https://twitter.com/NAChristakis/status/1276108130125066241?s=20
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11/x https://twitter.com/NAChristakis/status/1276108130125066241?s=20
It seems the pandemic has stopped in that community, with a high antibody prevalence of 42.4%. Notably, children were less likely to be infected.
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In another study, it was also shown that children are less likely to be infected, with a hypothesis being that this is driven by lower expression of the ACE2 receptor.
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13/x https://twitter.com/CMichaelGibson/status/1275392507191443458?s=20
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13/x https://twitter.com/CMichaelGibson/status/1275392507191443458?s=20
Another fascinating study of a ship expedition to the Antarctic showed that even in close proximity a significant faction of people did not become infected.
H/T @vmontori
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14/x https://twitter.com/VincentRK/status/1275838416236580867?s=20
H/T @vmontori
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14/x https://twitter.com/VincentRK/status/1275838416236580867?s=20
So it seems likely we cannot estimate the fraction of susceptible individuals by merely determining this by the lack of specific SAR-COV-2 protective antibodies.
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How could this be? Is it possible not all are likely to be infected? I suspect this is multifactorial and mostly hypothetical. I will share two possibilities others have explored.
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The most likely explanation is that there are some mechanisms that have evolved over the course of human/primates/mammal evolution and that there is some possibility of cross-immunity derived from other coronaviruses.
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This is hard to prove but it is possible that evolution has selected traits making humans more resilient to coronaviruses exposure. Perhaps our ancestors or even lemurs already had major existential threats in the past! Thank you!
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https://images.app.goo.gl/iDmZbMA8xAiS8H4g9
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https://images.app.goo.gl/iDmZbMA8xAiS8H4g9
How could we be protected? It is impossible to tell. Our knowledge about coronaviruses is limited as is true for most science. Maybe polymorphisms in receptors, immunity, or other ways. We might never know. But we do know evolutionary pathways select
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Another possibility is cross-reactivity to other coronaviruses. One such study has shown that as a possibility. They found T cell reactivity from viable T cells stored before SARS-CoV-2. In nearly one-half of cases!
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20/x https://twitter.com/Rfonsi1/status/1264572312025628672?s=20
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20/x https://twitter.com/Rfonsi1/status/1264572312025628672?s=20
This study was small but very provocative. If confirmed, this means that these individuals with such reactivity would need to be subtracted from the "S" (as in susceptible). In other words, you can be functionally "immune" even if not exposed
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21/x https://twitter.com/Rfonsi1/status/1264572313900441606?s=20
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21/x https://twitter.com/Rfonsi1/status/1264572313900441606?s=20
Importantly, and somewhat obvious, they will not have typical SAR-CoV-2 antibodies. But they may still have protective cross-reactive antibodies against other coronaviruses.
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It would be fascinating to test for such immunity and antibodies in close contacts of infected individuals who did not become sick. Low hanging fruit!
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Modern science has the capability of presenting an array of targets (proteome) of coronaviruses to test for the presence of these antibodies.
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It is possible a high viral dose can overcome some level of cross-immunity. That would explain why there are clusters among families or friends. And also some of the cases reported in healthcare workers.
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Globally we have heard from colleagues in Peru, Ecuador and Greece saying βthe parking lots were full, we had no more beds. They are goneβ
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The problem is we have no reliable way of knowing who is susceptible, and how is not. I do not recommend anyone reads this as a way to relax our safety measures. But hopefully this give you hope.
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@Vmontori highly recommends I read the A Camus book. Highly descriptive of the current situation.
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In the meantime stay safe, use masks in public, quarantine yourself if ill. And remain hopeful.
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