Thread by @AtomsksSanakan

1/C

A lot of COVID-19 contrarians abuse the idea of "cross-reactivity" to make SARS-CoV-2 (the virus that causes COVID-19) look less dangerous than it really is. Many of them do this to avoid policies they dislike, like lockdowns.

So let's get into that

2/C

Some basics:

Immune cells known as T cells and B cells have receptors that recognize viruses.

Think of the receptors as a lock, + portions of the virus as a key; i.e. the lock (receptor) binds to a specific key (virus region), + not to other keys

3/C

Even if you've never been infected with a virus, bacteria, etc., you almost certainly have T + B cells that recognize it.

When you're first infected, those cells (especially B cells) take a few days to increase in number (and activity) + generate their full immune response.

4/C

But if you're re-infected, T + B cells reach their full response quicker + better. That's what makes the T + B cell response *adaptive*; it improves w/ re-infection.

Vaccines typically work by mimicking a 1st infection, so u respond better later

slideshare.net/Pratheepsandra…

5/C

Sometimes two different viruses, bacteria, etc. are similar enough that the same T cell receptor or B cell receptor recognizes both of them.

In other words: 1 lock recognizes more than 1 key.

This is known as "cross-reactivity".

frontiersin.org/articles/10.33…

6/C

So imagine a coronavirus that causes a cold infects u.
Then suppose SARS-CoV-2 (a different coronavirus) later infects u.

If u have cross-reactive cells that recognize both coronaviruses, your immune system could treat SARS-CoV-2 as a re-infection of the 1st coronavirus.

7/C

This is where the COVID-19 contrarians/denialists come in to distort the science.

Many of these contrarians *assume* that cross-reactivity acts like a very beneficial vaccine that makes you immune to SARS-CoV-2.

8/C

One mistake involves non-experts messing up on terms like "immunity".

We immunologists can use those terms to mean generating a immune response, such as a T cell receptor binding a virus. That is not necessarily the same as being "immune" to infection, disease, etc.

9/C

Another problem is contrarians overlooking other impacts cross-reactivity can have.

Cross-reactivity from cold coronaviruses could be:
1) beneficial
2) useless
3) harmful

Contrarians evade options 2 and 3.



nature.com/articles/s4157…

10/C

I've discussed elsewhere how cross-reactivity can be harmful.

Some core points:
- SARS-CoV-2 can exploit your immune response to make u sick
- immune response specific to a cold coronavirus could work badly on SARS-CoV-2

11/C

On harmful immune responses to SARS-CoV-2:
academic.oup.com/nsr/article/7/…
link.springer.com/article/10.100…
medrxiv.org/content/10.110…

Helpful video below from @c0nc0rdance on how cross-reactivity is know to be harmful in other conditions:
51:59 - 54:06 :

12/C

Another risk is that u may need "naïve" immune cells; i.e. cells that haven't bound to a virus before binding to SARS-CoV-2.

Binding previously to a cold coronavirus means they're not naïve.


cell.com/cell/fulltext/…

medrxiv.org/content/10.110…

13/C

Cross-reactivity could instead be useless because:

- SARS-CoV-2 better evades the immune system than do cold coronaviruses [hence why SARS-CoV-2 is more deadly]
- the immune response to cold coronaviruses doesn't last long enough

nature.com/articles/s4159…

14/C

Cross-reactivity might also be useless because infection with SARS-CoV-2 generates a different and *better* immune response to SARS-CoV-2 than does prior infection with a cold coronavirus.

science.sciencemag.org/content/early/…

web.archive.org/web/2020061800…

15/C

So in my opinion, it's unlikely that cross-reactivity from cold coronaviruses is very beneficial to the immune response to SARS-CoV-2.



medrxiv.org/content/10.110…

medrxiv.org/content/10.110…

16/C

Folks should also remember that SARS-CoV-2 managed to kill over a million people, even with cross-reactivity being present. So cross-reactivity clearly is not enough to prevent this virus from infecting and killing large numbers of people.

17/C

And before some politically-motivated contrarian says:

'Well how do most people avoid getting sick without cross-reactivity?!'

Look up what the "innate immune system" is. Also, one doesn't need cross-reactivity to generate a T + B cell response.

18/C

So beware if a non-expert tells you cross-reactivity is some saving grace from SAR-CoV-2, especially if that non-expert is politically-motivated to make SARS-CoV-2 looks less deadly in order to evade policies they dislike (like lockdowns):

judithcurry.com/2020/07/27/why…

19/C

I'll post more sources below, along with the parts of the thread they're relevant to. Might update this thread as needed.

For part 14/C:
medrxiv.org/content/10.110…

For part 13/C:
medrxiv.org/content/10.110…

20/C

Re: "COVID-19 contrarians abuse the idea of "cross-reactivity" to make SARS-CoV-2 (the virus that causes COVID-19) look less dangerous than it really is."

I'm fed up with politically-motivated non-experts (see part 7/C).



archive.is/pAvqj