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Comment by acwan93 | Hacker News Reader

Wasn't there news about how as a virus mutates over time it becomes less severe, but more transmissible? Something about where the virus just wants its host to live long enough to transmit the virus to someone else so it can continue passing its genetic data over. It seems like Omicron could be following this pattern.

If you have too severe of a virus, then all its hosts are killed and it can't live on. Too weak of a virus and the host's immune systems will kill it before it has a chance to transmit.

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> Wasn't there news about how as a virus mutates over time it becomes less severe, but more transmissible?

That's sort of a rule-of-thumb, not a fixed law. In the case of covid there's a relatively long period of time (up to several days) in which people can spread the virus without yet showing symptoms. As such there isn't a lot of evolutionary pressure for it to become less virulent.

True, there's no selective pressure for it to become less lethal.

But I wonder: isn't a random mutation unlikely to improve on any of its profiles (transmissibility or lethality)? If so a more transmissible virus is unlikely to also be more lethal.

What if (not sure) a random mutation actually tends to do slightly worse? Then more transmissible viruses tend to be less lethal over time.

Sure we still get more lethal mutations from time to time, but the more transmissible ones are the ones which win out.

> random mutation unlikely to improve

indeed, but subsequent success or failure does. Mutation and selection. Mutation prepares the pool to sieve the successful ones.

Yes my point is, when you do improve one (transimissibility) you probably did not improve the other one (or even got worse at it).

I'm no expert but my understanding is that unfortunately there is some correlation between transmissibility and severity of disease, because one of the ways it can become more transmissible is to reproduce in your cells faster so that you shed more virus particles. This also means it takes over quicker and your immune system has less time to respond before it does lots of damage.

Whether that outweighs the randomness you describe I don't know. Maybe nobody knows for this virus?

Well if the two events (improved transimissibility and improved lethality) are not independent as I assumed then it's certainly bad news.

I also heard the opposite thesis btw, higher transimissibility might sacrifice something in terms of lethality. Like you can't really add much as I'm not an expert.

The people have dramatically altered their behavior on a global scale (on average anyways) because of COVID’s lethality. There is absolutely selective pressure in that dimension.

If the lethality of Covid were to drop to seasonal flu levels there wouldn’t be anywhere near the amount of research into medical interventions nor would we feasibly maintain our current levels of public health interventions.

Don't really get your point.

> The people have dramatically altered their behavior on a global scale (on average anyways) because of COVID’s lethality. There is absolutely selective pressure in that dimension.

This reads to me: "Covid is certainly more lethal than the average flu, therefore is undoubtedly getting less lethal" (effect of selective pressure). It doesn't make much sense.

> there wouldn’t be anywhere near the amount of research into medical intervention

Right, how's that has to do with whether there's selective pressure or not?

It almost feels like you are attributing a different meaning to "selective pressure", but cannot understand which one.

You seem to misunderstand what selective pressure is.

Selective pressure is anything that disrupts replication. If people take measures to prevent spread of a disease that’s literally selective pressure. I don’t understand what is confusing about that concept.

I think you're too quick at making assumptions which are not correct unfortunately. Let's recap:

> there's no selective pressure for it to become less lethal.

> If people take measures to prevent spread of a disease that’s literally selective pressure.

How trying to slow down its spread can "force" it to become less lethal?

The only possible answer is that lower lethality gives it more time to spread around right?

It turns out Covid has a long incubation period, in fact plenty to use the host to infect other people.

Tl;dr: Given the length of the incubation period a less lethal virus would not gain much in terms of its ability to spread. That's the thesis I'm hearing.

With delta and asymptomatic transmission this wasn’t totally the case iirc.

Increased viral load in the asymptomatic phase increased virality, but also increased deadliness once the symptoms started. At least that’s what I recall reading. Normally you’re correct, but it doesn’t necessarily need to be that way.

Hopefully we’re lucky and it’s both way more transmissible and way less deadly, but no one knows yet.

Delta was more severe than the original strain, but there was some evidence indicating it was slightly less severe than Alpha (and much more transmissible than Alpha).

In order for this to occur, there needs to be a selection pressure. It doesn't just magically happen.

The virus behind Marek's disease in chickens hasn't gotten less severe over time, it's gotten much, much more severe, as an example. HIV does not seem to have gotten less severe, nor smallpox.

The virus behind Marek's disease in chickens got much more severe because of the leaky vaccine used on chickens.

Here's some introductory material:

  https://www.pbs.org/newshour/science/tthis-chicken-vaccine-makes-virus-dangerous

  https://www.nationalgeographic.com/science/article/leaky-vaccines-enhance-spread-of-deadlier-chicken-viruses

  https://www.youtube.com/watch?v=haRMKsI-jKY

And here are a couple of papers:

  https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002198

  https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002236

Yes, Marek's is actually a good illustration of how diseases can go in the other direction.

This is true (and hopefully so w/ Omicron) when looked at a long enough time scale.

The real concern is if we're currently in the "still getting worse before it gets better" part of the timeline.

We're all waiting to see how many severe hospitalizations occur w/ a large enough population.

>If you have too severe of a virus, then all its hosts are killed and it can't live on.

Ever played "Plague Inc" ?

Its a fascicle way to show how this model is unlikely to play itself out in todays hyper mobile population.

That's the theory behind spanish flu mutating into the less severe seasonal flu strains we learned to live with.

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