T. Ryan Gregory Profile picture
Dec 27, 2023 15 tweets 3 min read Read on X
🧵

There are 7 human coronaviruses (so far).

Four of them cause the "common cold" (229E, NL63, OC43, HKU1).

The three most recent are deadly (SARS-CoV, MERS-CoV, SARS-CoV-2).

All three of the deadly ones use the ACE2 receptor. Only one of the common cold viruses (NL63) does.
We have never in the history of our species encountered a situation anything like this one, with a coronavirus that is infecting *billions* of hosts, year-round, repeatedly up to several times per year, and being transported all over the world through mass global travel.
In short, we cannot simply look to other human coronaviruses and draw conclusions about what SARS-CoV-2 will do longer term.

SARS-CoV-2 has already proven itself not to be a "textbook virus". Rather, the textbooks will need to be revised significantly because of it.
Also, here's a reminder that the following are *myths* / *misconceptions*, with no basis in either experience or theory:

❌ That viruses always automatically evolve to become benign so they don't drive their hosts extinct.
Myths / misconceptions cont'd:

❌ That humans have evolved alongside pandemic-level respiratory viruses for millions of years. That's bats. We're not bats. Robin: "Humans evolved with these viruses for millions of ye-"  Batman, striking Robin: "You're not a bat!"
Myths / misconceptions cont'd:

❌ That a virus like SARS-CoV-2 evolves slowly or will soon run out of evolutionary space. This neglects the fact that there is an absolutely enormous population size of the virus and that it is evolving in a changing fitness landscape.
Myths / misconceptions cont'd:

❌ That a pathogen becoming endemic means it is no big deal. Also endemic: malaria, tuberculosis, measles, etc.

nature.com/articles/d4158…
Myths / misconceptions cont'd:

❌ That the immune system is like a muscle that gets stronger with repeated infections and weaker if not exercised through exposure to *pathogens*. Don't confuse this with the "hygiene hypothesis", which is about exposure to *commensal* microbes.
In the same way that we cannot make assumptions about the evolutionary trajectory of SARS-CoV-2 or the effects of (and on) immune systems, we need to reject expectations built on myths and misconceptions.
Every day there are new discoveries about what SARS-CoV-2 does to our bodies. Those proclaiming an end to waves have been proved wrong over and over. Optimistic predictions about the mildness or lack of potential spread of new variants have not survived collisions with reality. No one could have foreseen this.
We do not know what SARS-CoV-2 will do.

There is no simple, linear evolutionary path that it must inevitably follow.

There is no precedent on which to confidently base predictions.

What we can say with some confidence is that more virus is a bad thing.
Quick correction:

MERS-CoV uses the DDP4 receptor, but close relatives of the virus do use ACE2.

The point remains that the deadly viruses are not obviously just cold viruses we're not used to yet.

nature.com/articles/s4142…
(Correction: MERS-CoV uses DDP4 although close relatives do use ACE2. See tweet at the end of the thread.)
Oh, and SARS-CoV-2 doesn't only use ACE2, we are still learning new things about how it can enter cells using different receptors.

nature.com/articles/d4397…
(h/t for the reminder about MERS and DDP4 to @nzm8qs in our variant tracker group!)

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More from @TRyanGregory

Jan 18
As you read more and more reports of uncommon pathogens infecting a lot of people, or common pathogens surging far more than usual and/or having unusually severe effects, please remember that this is what immunity theft predicts and what we've warned about for years.

1/
By contrast, "immunity debt" or "post-pandemic normalizing of levels" as an explanation makes less and less sense as more time goes by. In 2025, it is absurd to still be talking of new surges of illness being due to the lack of immunity from mitigations that ended years ago.

2/
Case in point, we wrote this more than 2 years ago.



3/calgaryherald.com/opinion/column…
Read 4 tweets
Jan 15
Lots of things in biology correlate with "latitude" (biodiversity, population size, body size, etc.), but "latitude" itself isn't a thing in and of itself. What actually matters is photoperiod, temperature, precipitation, etc. That's how we should think of "seasonal" as well.

1/
Viral transmission may be strongly and predictably "seasonal", mostly occurring during certain times of the year (flu, RSV), but it's not either-or. Other viruses may be common year-round but also increase at certain times of the year.

2/
However, it's not "season" per se, it's things that vary throughout the year. Mostly this involves human behaviour (travel, congregating, being indoors more, school in or not, etc.). There may also be effects of environmental variables like UV, wind, temperature, humidity.

3/
Read 5 tweets
Jan 12
So, I'm not sure the American right has thought through the implications of annexing Canada yet.

A few things to consider...

1/
First of all, Canada has a slightly larger population than California, so presumably we'd get at least 54 electoral college votes in presidential elections. Polls here showed that about 61% of Canadians would have voted for Harris and 21% for Trump.



/2globalnews.ca/news/10830218/…
Now, it would be pretty weird and surely a big ego bruiser to have one state being physically larger than the entire rest of the country combined, especially if it's blue on the electoral map. So presumably Canada would represent several states, not one.

3/
Read 10 tweets
Dec 5, 2024
(Sarcasm alert) The way viral evolution works is that if you have a naïve idea of how it works and that helps with calm-mongering, that's how it works. Need some examples? 🧵
For example, if it helps with calm-mongering to think that viruses have to evolve to become mild or else they will drive their hosts and themselves extinct, that must be what happens. Don't let actual evolutionary biologists convince you otherwise! (Sarcasm)
Oh, oh -- how about this? If a virus can infiltrate the host's genome permanently and then not cause any harm, that would give it a huge advantage in long-term survival. Therefore, all viruses must evolve to become endogenous in the genome! This is fun! (Sarcasm)
Read 4 tweets
Nov 8, 2024
One side is consistently painted as violent and the other as being unsafe. Is that accurate? Well, all of these happened on video in Ontario, Canada. 🧵
Attacking with a nail gun while shouting "All Palestinians will die".

Read 8 tweets
Nov 4, 2024
How sure are you that only certain people are susceptible to severe acute COVID, and that you're not one of them?

What is your level of certainty that only specific people are vulnerable to long COVID, and that you're not one of them?

1/
Are you certain that repeated SARS-CoV-2 infections won't have cumulative effects?

How confident are you that you don't, or won't ever, harbour a persistent SARS-CoV-2 infection?

Are you totally convinced that SARS-CoV-2 will necessarily become mild and seasonal?

2/
Do you truly believe beyond doubt that "immunity debt" explains the surge in other infectious diseases, years after most major mitigations were dropped and even among kids who weren't born yet during lockdowns?

3/
Read 4 tweets

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