
A T Cell Army against SARS-CoV-2 - karmel
https://www.hellovirology.com/2020/08/a-t-cell-army-against-sars-cov-2.html
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jonplackett
I'm not a virologist or anything close, but reading this it seems like
definitely good news?

If I am understanding it right, it's saying many people already have T-cells
from common colds that can to some extent recognise Covid-19, and those that
have had Covid, even a mild case, have T-cells that seem to last quite a
while.

~~~
dalore
Yes, this confirms what a few people have been trying to say, that we do have
some form of prior immunity, it's not a novel virus in that everyone is 100%
susceptible, and that anti body tests won't show up prevalence. In addition
means we need a lower rate for herd immunity, if we haven't already got it in
some places like New York and London. So the models of exponential growth was
unfounded and it follows more a natural gompertz curve.

~~~
graeme
Not quite. Carl Bergstrom had a good thread on this. Basically, we saw a
certain rate of growth. If this rate of growth happened despite half the
population having T cell immunity, then it means the R0 must be higher than we
thought, and therefore the herd immunity threshold in the susceptible
population rises.

You do get a somewhat lower overall herd immunity threshold, but less than you
thought.

[https://twitter.com/CT_Bergstrom/status/1290744393796694016](https://twitter.com/CT_Bergstrom/status/1290744393796694016)

~~~
timr
That doesn't make any sense. The key part of Bergstrom's logic is here:

 _" But ex post, holding the epidemic trajectory constant, it means that the
disease is more transmissible per contact event than you expected."_

...but that's wrong. The epidemic trajectory _isn 't_ constant (R0 is not an
innate property of a virus; it changes with context), and it's pretty likely
that we've completely mis-measured it by sampling from the wrong population.
Our estimates for R0 are mostly model extrapolations from PCR testing data,
which are not uniformly sampled from the population. If anything, in fact,
they're heavily biased _toward the susceptible population_.

In other words, because we're sampling disproportionately from the most
susceptible population, our estimates of R0 _already_ seem high. If you
sampled _randomly_ from the population of less-susceptible people, you would
see that the R0 is much lower than you originally predicted.

On top of that, there's absolutely no reason to believe that cellular immunity
would make it seem like R0 is lower in any particular population: T-cell-
mediated immunity is a late response. It can reduce the severity of an
infection, but it's still highly likely you'd show up as a positive PCR test,
and count toward an R0 estimate.

So you have a measurement based on a test that isn't strongly affected by
cellular immunity, derived from a population biased toward the most
susceptible individuals. If you have to doubt something here, you doubt the
estimate of R0 (i.e. the model), not the observations of reality.

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chrisgd
2021 will be the year of T-cells given this news and the continued growth of
CAR-T therapy

~~~
qserasera
agreed

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nradov
This previous discussion covers the same topic:

[https://news.ycombinator.com/item?id=24076096](https://news.ycombinator.com/item?id=24076096)

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orblivion
So is anybody floating the crazy idea of giving every reasonably healthy
person a dose of the common cold as a poor man's vaccine?

~~~
ProcNetDev
Some people want to start giving out Oral Polio Vaccine (OPV) because it kicks
the immune system into action. It is very safe, if you have already had a
polio vaccine. I believe it has been shown that OPV reduced seasonal flu in
areas where it was distributed.

[https://science.sciencemag.org/content/368/6496/1187](https://science.sciencemag.org/content/368/6496/1187)

~~~
acqq
Your link refers to the following clinical trials for BCG, running since
March:

[https://clinicaltrials.gov/ct2/show/NCT04327206](https://clinicaltrials.gov/ct2/show/NCT04327206)

[https://clinicaltrials.gov/ct2/show/NCT04328441](https://clinicaltrials.gov/ct2/show/NCT04328441)

It seems there are no current clinical trials for OPV, just that author
arguing that such trial could be started (first time in April).

BTW, looking at how polio manifested, it really is a good example about what
viruses are able to do, and why only counting "dead" (as in CFR or whatever)
misses the point:

[https://www.cbc.ca/news/canada/manitoba/covid-19-is-
threaten...](https://www.cbc.ca/news/canada/manitoba/covid-19-is-threatening-
to-us-past-epidemic-leaves-survivors-at-risk-1.5510947)

"Polio often destroyed nerve cells that controlled muscles, leaving some with
paralyzed limbs or lungs."

