Comment by subsubzero | Hacker News Reader

Comment by subsubzero | Hacker News Reader

Some up to date news regarding T-cells and their implications suggest this in fact could be a thing with some of the harder hit states. Apparently T-cells will "remember" an infection after a person is exposed to and recovers from covid-19[1]. This is a huge development as it suggests that neutralizing antibodies are not the only defense against a reinfection of covid-19(and these antibodies only last a few months) whereas T-cell memory of infections lasts years.

Also, there are some signs that other cornavirus family of viruses(common colds, not covid-19) could trigger a memory with these t cells, this is a possibility why some have extreme cases and others show no signs of sickness[2]. Couple these points with data showing 40% of people who contract the virus are asymptomatic[3] this leads to the idea that alot more people have had the virus than what is reported, which in this case is a good thing as its closer to herd immunity(if all the above is found to be true).

[1] - https://www.businessinsider.com/long-term-coronavirus-immuni...

[2] - https://www.livescience.com/common-cold-coronaviruses-t-cell...

[3] - https://www.washingtonpost.com/health/2020/08/08/asymptomati...

yes agree. And the CDC reports there are 10X the cases of COVID than has been reported based on antibody studies. And there are many more deaths than have been reported https://realscience.community/2020/08/16/why-a-lot-more-peop.... All reasons that we are closer to herd immunity than is the common perception.

Doesn’t herd immunity for a country of 350 million need somewhere on the order of 220 million to have been exposed and recovered? I don’t think we’re anywhere near that yet.

We are at around 50,000,000 cases. It is looking like herd immunity or at least R<1 is happening at around 30%. There are five states so far that have reached that point- NY, NJ, LA, FL, and AZ. So we have 45 more states to go. As a nation we aren't there yet. I would guess that in a few months we will be given the pace at which this is happening.

This has been reported from a number of places as a possibility.

Coronaviruses are a member of the virus group that give us common cold and one theory is that the common cold has cross reactivity with Covid immunologically.

So there may be a huge population with built in immunity.

Sweden has had tiny amounts of deaths for weeks, New Zealand, I think Italy and some other countries as well.

It's not just the U.S. it's other countries.

> We are at around 50,000,000 cases.

Where is that number coming from? If you were talking about United States, you were off by a factor of 10! If you’re talking about the whole world, you’re still off by a factor of two! At least as far as confirmed cases goes.

We can all assume the number of actual cases is greater than the number of confirmed cases. How much greater, it’s really hard to say, especially as testing has ramped up significantly and I even know Americans who are getting multiple tests with quick responses in certain locations. So you can’t just make up a number as a guess and then use it as evidence.

The CDC has said we are underestimating infection rates by a factor of 10 based on antibody testing. We have undertested the population and therefore have only captured 10% of the cases.

How do you define that 220 is the right number?

It’s an estimate based on the probability of a virus finding new hosts. the higher the proportion of potential hosts that are immune, the less likely the virus is to spread.

Herd immunity is the threshold where the replication rate falls below 1. It's not the point at which transmission stops. The disease will continue beyond that point.

Thats, uhm, very limited understanding. Currently behavioral changes (mask, etc) are much larger factors affecting R0 and none of them have any bearing on hwrd immunity.

Plus we are finding that traditional herd immunity (aka just let the disease rampage) may come at the cost of heart disease in a majority of cases.

Of course they have an effect on herd immunity. If behaviour changes then the replication rate changes and hence the herd immunity threshold changes.

Is it based on any kind of evidence? Just wondering if we have ever measured this kind of number in any way.

Herd immunity means roughly 70% of a population has antibodies so the chance to spread to new hosts is low.

> Apparently T-cells will "remember" an infection after a person is exposed

That is not a "huge development". The basic workings of the immune system have been known for decades. I used to think this was common knowledge.

The huge development is that they found this T-cell mechanism active already in relation to covid-19 for a large percentage of sampled populations. Current antibody tests are only looking at B-cells.

It's good news and nobody talks about it.

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