Author Topic: Is there a second wave?  (Read 22205 times)

Offline how

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Re: Is there a second wave?
« Reply #555 on: June 21, 2020, 08:13:09 PM »
I don't know how severe they are I can ask.

If you can find out and report.

From Texas I heard that cases are less severe than 2 months ago

Offline chevron

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Re: Is there a second wave?
« Reply #556 on: June 21, 2020, 10:09:15 PM »
Florida is not NY. Florida never got hit like NY.
With each passing day, it is becoming more and more likely that NY/NJ will not see a significant second wave, unless immunity runs out before a vaccine is produced. In addition, many people are still distancing/wearing masks (though it decreases by the day), the government is testing enough and has great data transparency to help people make better decisions. There are still new cases in NY, but despite reopening and protests, the numbers continue to decrease.

Compare to Florida - lack of data transparency, encouraging people to go out unsafely, less herd immunity, it’s a bad recipe playing out in many states.

Well they are certainly different but don't tell me that New York has herd immunity.

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Re: Is there a second wave?
« Reply #557 on: June 21, 2020, 10:21:14 PM »
The cases are not less severe they are the same as they were a couple months ago

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Re: Is there a second wave?
« Reply #558 on: June 21, 2020, 10:21:25 PM »
Well they are certainly different but don't tell me that New York has herd immunity.

I didn’t say NY has herd immunity. I said Florida has less herd immunity, or if you want to be precise - NY has a higher percentage of residents with immunity.

Bottom line: more people with immunity means lower infection rate. But there are other factors at play as I have mentioned.

Offline biobook

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Re: Is there a second wave?
« Reply #559 on: June 23, 2020, 11:13:52 AM »
https://www.biorxiv.org/content/10.1101/2020.05.26.115832v1.full.pdf

This study “may” show that immunity which stems from T cells last a long time.

I didn't know enough to understand the article that @Afrages6 posted last week, so I detoured back to basic biology, then went back to the article, and then came up for air and wrote this TR of it all.  It's probably too simplified for many here, but it reflects my simplistic level of understanding, so let me know what I got wrong. 


Just how long will immunity to COVID last?
  We've usually answered this by discussing how long antibodies remain in the blood, but maybe other parts of the immune system are more important.  Let’s look at those other parts, and they help defends against a virus.

We have some general mechanisms to prevent damage – multiple cell layers in our skin, hairs in our nose, cilia in our airways, sticky mucus on exposed surfaces, like tears in our eyes and mucus in the nasal passages.  These  block entry by the myriad bacteria, viruses, and fungi that we come into contact with every day, when we touch a doorknob or breathe in a public restroom, for example.  They work immediately upon contact with an infectious agent, and aren’t picky about what it is, so they’re sometimes called innate immunity, there from the time we’re born. 

Innate immunity prevents a lot of infections, but not all.  Other immune responses develop only after we’re exposed to a particular infectious agent, making up what’s called specific immunity, so let’s take a look at what is meant by specificity.

Imagine you hold a kiddush cup with a stem in your hand, your fingers pressed snugly around the bumps and ridges in the stem.  Now imagine removing the cup, while your hand remains frozen in place, forming a mold that specifically fits that stem.  With eyes closed, you’d be able to use that hand to feel around the china cabinet… past the esrog box…past the candlesticks…then, punkt!  Your molded hand “recognizes” the kiddush cup.  But one day you get fooled.  You’re reaching in with your molded hand… and when you open your eyes… you’ve got a besomim box!  Some artist created a Havdalah set with the the identical stem on the cup and besomim box.  We could say that your molded hand, designed to react specifically with the stem of the kiddush cup, also cross-reacts with the similarly-shaped stem of the besomim box.
 
In the human body, many processes depend on this sort of recognition, where the 3-D structure of one protein molecule matches up exactly with another protein, and that connection leads to some change in the cell.  In addition, cross-reactivity happens, when a protein made to recognize X happens to also (inappropriately) recognize Y. 

In the immune system, two kinds of cells produce these sorts of proteins with specificity. 
B cells make antibody proteins, and release them into the fluid that surrounds the cell.  Antibodies can be isolated from the fluid part of blood, known as plasma.  Antibody activity is also known as humoral immunity, because it occurs in the body’s fluids (not funny!  humoral, from the same root as humidity, meaning fluid). 

T cells make a protein called TCR, which, like antibodies, can match up with a specific target protein.  But T cells don’t release TCR, rather they keep it stuck in their outer membrane, and it’s the cell with TCR that actively fights infection.  This is called cellular immunity

Incidentally, although we talk about antibodies and T cells as being part of the blood, they are, in fact, both found throughout all the tissues of the body.  They’re just usually studied in blood, because people are more willing to donate a pint of blood than a pound of flesh. 

If we were to look at all the blood’s B cells under the microscope, they’d look pretty much alike, but at a chemical level, they’re quite varied.  One cluster of B cells make only antibodies that recognize a measles virus, another bunch make antibodies that recognize chicken pox, another might recognize a particular cold virus.  Similarly there are separate T cells with TCRs that are specific for measles, others specific for chicken pox, etc.  And cross-reactivity can happen, when an antibody or TCR made to recognize X can also recognize Y. 

Antibodies and TCR can recognize a particular protein on the surface of a virus, which in COVID, is often the Spike protein.  Pictures of the COVID virus show a ball with RNA inside and various proteins protruding outside.

Specific immune response - virus in blood

Now let’s go back to that virus that wasn’t stopped by the non-specific immune responses, and now finds itself in the fluids of the body.  Fluids released from the body, such as tears, saliva, and nasal mucus contain IgA antibodies.  If there are IgA antibodies specific for COVID, they’ll attach specifically to the spike protein, and thereby neutralize the virus, preventing it from doing further damage.

If the virus manages to get deeper into body fluids such as into blood or lymph, they’ll encounter IgG antibodies.  Again, IgG antibodies specific for the COVID spike protein will attach and neutralize the virus.  These fluids also contain macrophages, large cells that scoot around between the other cells of our body, much like the ameba you may have seen moving across a microscope slide in a biology class.  Macrophages engulf and digest the neutralized virus, breaking it down into smaller molecules that can then be recycled and reused.  Macrophages act nonspecifically, so can engulf a wide variety of particles – viruses, bacteria, particles of air pollution, what have you. 

Specific immune response - virus inside cell

A strong antibody response may stop the virus in its tracks, but if that doesn't happen, the virus can reach its final destination, the inside of a human cell.  The Spike protein on the virus surface, unencumbered by antibody, is now free to make a different protein-protein connection, and binds to ACE2, a protein on the surface of certain human cells.  This connection acts like a knock on the door, allowing the virus to enter the cell. 

Once inside, the virus takes over the cell’s machinery, forcing it to churn out copies of viral proteins and viral RNA.  The human cell has been transformed into a virus-making factory.   Viral RNA and proteins are then packaged into new viral particles which are discharged from the cell and go on to infect other cells.  The infected cells, prevented by the virus from doing all their own normal human stuff, eventually dies off. 

The kind of damage this does to the body will depend on where the infected cells are.  ACE2, the protein that the COVID virus first latches on to, is found in the lungs, digestive tract, and blood vessels, and all of these have been shown to be affected in COVID patients.

But the body doesn’t stand idly by and allow its cells to be infected by viruses – there’s an app for that!  It’s the T cell, and specifically killer T (or cytotoxic T, or CD8), which has a TCR protein on its surface that specifically recognizes a part of the COVID virus after it has infected a human cell.  The T cell sidles up to a COVID-infected cells, and the TCR-COVID protein-protein attachment leads the T cell to send a chemical signal (cytokine) that causes the infected cell to self-destruct.  Don’t worry, you won’t miss the loss of the cell - you’ve got 30 trillion more. The viral components are dispersed in the fluid, where they can be neutralized by antibodies and gobbled up by macrophages.
 
So this two-pronged approach, by antibodies and killer T cells, can effectively rid the body of the virus.  Another T cell, called T helper (CD4) coordinates the activity of the B and T cells.

Long-term immunity


The first time we’re exposed to a new virus, it can take 5-10 days for the B and T cells to make enough antibodies and TCR to fight this specific infection, and in the meantime, the virus has time to infect our cells and we get sick.  Only as sufficient antibodies and T cells are produced do we start to recover.   Memory B cells and memory T cells are also produced, and remain in our body after we recover.  The next time we’re infected with that same virus, the B and T cells make the specific antibody and TCR so quickly that they overpower the virus before it gets a chance to do any damage, and we're considered immune to that virus.

So our original question, How long does immunity to COVID last, can be rephrased as How long do memory B and memory T cells remain after COVID infection? And are those memory cells still able to fight infection? 

The new article

We can’t answer that for COVID, since the virus hasn’t been around for a long time, so Nina Le Bert and her co-workers asked a similar question regarding a similar virus that appeared 17 years ago, known as SARS.  SARS is also a coronavirus, in the same family as COVID, so it could give us a hint about what to expect from COVID.   (Proper names of the viruses are now SARS-CoV-1 and SARS-CoV-2, but I abbreviated them to SARS and COVID.)

With regard to humoral immunity (B cells and antibodies), some think this will be short-lived.  It was already known that people who had recovered from SARS in 2003 had antibodies at that time, but they were gone from the blood after 2-3 years.  A recent paper from China suggests that the same may be true of COVID antibodies, which start to diminish after just 2-3 months.  So it's not clear whether humoral immunity to these viruses is long-lasting.

What about cellular immunity (T cells)?  Do people who had been infected with SARS in 2003 still have T cells specific for SARS?  Le Bert tried to answer this by using proteins that were known to have been part of the SARS virus (the SARS virus itself has disappeared).  She mixed those SARS proteins with the blood of people previously infected with SARS, and found that in every single person the blood still contained T cells that could recognize those proteins.  They concluded that memory T-cells can last as long as 17 years after infection with the SARS virus, and makes us hopeful that those who’ve recovered from COVID will similarly have long-lasting cellular immunity.

Le Bert did another study, this time on blood which had been collected in 2019, so it was from people who definitely had not had either SARS or COVID-19 which were not around then.  Much to their surprise, half of these people did have T-cells that could recognize certain COVID proteins!  But we know that T cells are only made specifically for those foreign agents we’ve been exposed to, and these people hadn’t been exposed to COVID or SARS.   So where could these T-cells have come from?  Their best guess is that these people had once been exposed to yet a third virus, with a similar structure, which might have given them a mild cold, if anything.   T cells would have been made specific to that virus, but due to the similar structure of COVID, the T cells cross-react with the COVID protein.   

This is actually the third paper that @Afrages6 has posted, which show that even before COVID appeared, T cells that cross-react with COVID were already in the blood of some people. 

Implications

One implication of this is that it might explain why some people are exposed to the coronavirus but remain asymptomatic.  Perhaps these asymptomatic people had some long-term T-cell immunity based on their exposure to some unknown, related coronavirus, and this protected them from a serious infection.
   
Another implication of this is that it might change our concept of what is needed for herd immunity, something that @Afrage6 said weeks ago.  If 50% of people have some degree of immunity due to a cross-reacting T memory cell, and 20% have immunity because they actually came down with COVID and recovered, then we may have 70% immune, which may be close to herd immunity, even without a vaccine.  On the other hand, as @Lurker has pointed out, it’s possible that of the 20% who came down with COVID, half of those also had the cross-reacting memory T cells and they didn’t work, so maybe cross-reacting T cells are not as useful as we’d hope.

A few caveats:

Le Bert found T cells made in response to some older virus, that can physically cross-react with the COVID virus proteins.  But as @S209 noted we don’t yet have evidence that these T cells can actually fight off a COVID infection.   Even in the case where those who recovered from SARS have T cells specific for SARS,  we can’t be sure how effective those would be in fighting a second SARS infection, since the SARS virus has disappeared.

We don’t know if these findings will generalize to other people – When they say that 50% of people had some T-cell immunity before COVID, they are talking about 50% of the 18 people they sampled, which is just 9 individuals.  We can’t really extrapolate from that to conclude that 50% of 328 million Americans would show the same response.   These people also all lived in Singapore, so it’s possible that the viruses prevalent there were not common in the US, and that fewer Americans would have this particular T cell.

This research hasn’t been peer reviewed, that is, critiqued by immunologists who know something about the subject.

I still don’t understand how memory T cells would be enough to stop an infection – I thought they needed to be accompanied by antibodies, and here they seem to be saying that long-term cellular immunity would be enough to prevent infection.
 

Offline Lurker

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Re: Is there a second wave?
« Reply #560 on: June 23, 2020, 01:08:03 PM »
@biobook There's no way you weren't/aren't a teacher. You have a great knack for breaking down complicated science into an understandable "For Dummies" format. Thank you!!
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Re: Is there a second wave?
« Reply #561 on: June 23, 2020, 01:16:35 PM »
@biobook There's no way you weren't/aren't a teacher. You have a great knack for breaking down complicated science into an understandable "For Dummies" format. Thank you!!
+1000 should definitely be one.
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Re: Is there a second wave?
« Reply #562 on: June 23, 2020, 01:33:14 PM »

Offline Dan

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Re: Is there a second wave?
« Reply #563 on: June 24, 2020, 12:20:54 AM »
@biobook There's no way you weren't/aren't a teacher. You have a great knack for breaking down complicated science into an understandable "For Dummies" format. Thank you!!
+1, amazing!
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Offline Proisrael

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Re: Is there a second wave?
« Reply #564 on: June 24, 2020, 02:03:54 AM »
The cases are not less severe they are the same as they were a couple months ago

In Israel the cases are far far less severe....Ventilator use actually fell by 2 from 29 to 27 yesterday. And this is now 2 weeks after the jump has started.

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Re: Is there a second wave?
« Reply #565 on: June 24, 2020, 05:42:03 AM »
In Israel the cases are far far less severe....
Completely not true.

Ventilator use actually fell by 2 from 29 to 27 yesterday. And this is now 2 weeks after the jump has started.
Ventilators are not being used anymore until absolutely necessary.
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Offline Proisrael

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Re: Is there a second wave?
« Reply #566 on: June 24, 2020, 06:40:09 AM »
Completely not true.
Ventilators are not being used anymore until absolutely necessary.

Well maybe the media is lying and you have a secret source to help fuel unnecessary panic.

https://en.globes.co.il/en/article-covid-19-cases-skyrocket-as-govt-restricts-hotspots-1001333423

Offline B.D.Da'ehu

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Re: Is there a second wave?
« Reply #567 on: June 24, 2020, 06:53:48 AM »
Well maybe the media is lying and you have a secret source to help fuel unnecessary panic.

https://en.globes.co.il/en/article-covid-19-cases-skyrocket-as-govt-restricts-hotspots-1001333423
The most important number to watch is serious cases. If you look at the numbers you'll see it has consistently risen over the last few weeks. In the latest update today it's back up to 45.


The fact that most positives now are younger people does make that number go up more slowly, however as more and more test positive overall we unfortunately are seeing a consistent rise in those in serious condition.

Offline Proisrael

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Re: Is there a second wave?
« Reply #568 on: June 24, 2020, 08:30:40 AM »
The most important number to watch is serious cases. If you look at the numbers you'll see it has consistently risen over the last few weeks. In the latest update today it's back up to 45.


The fact that most positives now are younger people does make that number go up more slowly, however as more and more test positive overall we unfortunately are seeing a consistent rise in those in serious condition.

The number on Sunday was 49 then fell to 40 now back to 45. Still less then Sundays numbers. Ventilators was at 29 fell to 26 and now at 27. These numbers are far better then the begining where severe cases were about 3-4% of total cases.

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Re: Is there a second wave?
« Reply #569 on: June 24, 2020, 08:40:51 AM »
The number on Sunday was 49 then fell to 40 now back to 45. Still less then Sundays numbers. Ventilators was at 29 fell to 26 and now at 27. These numbers are far better then the begining where severe cases were about 3-4% of total cases.

Remember that the first time around, we had little idea what we were looking for and public knowledge was close to zero, so by the time someone tested positive, there was a very short amount of time before the infection became serious. Now that we're catching it very early, it will take that much longer for an infection to become serious. It's also very likely that early treatment will keep many cases from becoming serious in the first place.

All of the above is good news. It also says nothing about the seriousness of the virus itself. Early detection and treatment doesn't mean the virus has weakened. It means we're doing what we're supposed to do. However, if the spread becomes exponentially worse, there is a good chance that more and more cases will avoid early detection and treatments will get delayed, causing serious cases to rise again.

(Hishtadlus, yada yada, you've heard this part before...)
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