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Comment by cableshaft | Hacker News Reader

One thing that makes Covid-19 a bit different from other viruses that have trended towards milder infections is its long incubation time (while still being infectious). So it can already spread pretty easily even if it's killing those people, and thus there's not a lot of darwinian pressure to become milder.

It might still trend towards that over time, but it will probably be slower at it than other viruses, and thus the 'it gets milder over time' aphorism about viruses doesn't apply as strongly to Covid-19.

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That’s only one pressure driving viral evolution.

Another pressure is social response to infection: so far, the predominant response to a more-virulent or more-lethal strain has been lockdown and/or other behavioral change, see: delta in India. On the flip side, a variant that causes milder symptoms is less likely to cause the same social response, which allows the virus to spread more widely.

This may (may!) be what we’re observing with Omicron. In any case, we’ll know much more in a few weeks.

I'd say that's normally true, but there's not a ton of lockdowns with even Delta right now, so while I agree that it probably isn't going to get worse, there's still not a ton of pressure from social response as it is right now for it to get milder (maybe you could argue pressure from vaccines I guess).

Yeah I think we can learn what society thinks is acceptable risk just by looking at death counts over the last two years. They've pretty much leveled out. So as the virus mutates into less (or more) harmful variations, we'll see the world react less (or more) strictly, but overall death count will remain stable.

Presumably the steady state will happen after the virus mutates into a less dangerous variant (as infecting more people will be evolutionarily advantageous for the virus), and eventually we all get it and build up antibodies, at which point its virulence further subsides.

Sure, and this is where the immune erosion comes into play: as vaccination rates go up, so does selection pressure for immune erosion.

Re: delta, think of this counterfactual — what would happen if a new variant appeared that is more lethal, more virulent, and that caused hospitalizations more quickly? You can bet the lockdowns would ratchet up.

With Omicron, we didn’t even notice it until there was a random genome scan. Viral evolution rarely selects for host death — it’s just not useful as a goal. There’s also probably relatively weak selection pressure for symptoms, though probably casing sneezes in hosts helps with spread, it also acts as a signal that can cause the host to isolate and halt spread. (See: SARS v1.)

From a selection pressure perspective, the ideal virus (among humans!) probably goes completely unnoticed for as long as possible. Humans won’t fight something they don’t even notice, and we probably have tons of these viruses everywhere and don’t even know about them.

Do you realise that mutation is not something the species can consciously control?

How could the virus have mutated to become milder to suit the social response if the society, as it stands today, is continuing to do what they previously did..?

There's likely millions of virus variants out there already. Some will evolve to become much more contagious and most won't do much of anything.

When a more severe variant starts dominating and everyone goes inside and stops spreading it that makes the more severe variant die out. As it dies out, and people go outside, variants that are milder will thrive because people won't lockdown as easily. This can repeat forever until eventually the virus is completely benign. Of course it's all based on randomness so it's not exactly predictable what will happen.

Except "Everybody goes inside and stops spreading" is not something that is unique to a variant of concern.

When everybody goes inside, all the variants stop spreading. The pressure is the same on every variants, so there's no source of evolutionary advantages on any variants.

> no source of evolutionary advantages on any variants.

Any variant that is able to co-exist with (rather than kill) its host during a full lockdown has a significant advantage. We co-exist with several coronaviruses already.

Only true if the virus lasts long enough to outlive a lockdown. So far that hasn’t been the case for the vast majority of single hosts.

> Except "Everybody goes inside and stops spreading" is not something that is unique to a variant of concern.

But it is — this will not be the response to a variant that doesn’t cause an increase in hospitalizations or deaths.

A given response exerts pressure on all variants, of course. But a milder variant may be able to spread widely before a more lethal one shows up and ratchets up lockdowns.

> When a more severe variant starts dominating and everyone goes inside and stops spreading it that makes the more severe variant die out

Except this doesn't happen, otherwise COVID would have already stopped spreading. Our social response to COVID isn't adequate enough to stop its spread. We can't get people to actually lock down or stop transmission.

The lockdown prevents severe mutations from replicating because of lockdowns. Milder mutations don't result in lockdowns hence ...

But has this been true in practice? Was any variant successfully stopped with lockdowns? I suppose hypothetically if there’s a new strain with like a 10% fatality rate there will be new extreme measures where that could be the case, but it hasn’t happened yet. Even the extreme early 2020 measures failed to stop the virus.

Which lockdowns in our hemisphere had the goal of stopping the virus? All I know about (or have been part of) never stated that goal, only goal was to break waves and avoid overload of health care systems, which most at least helped with.

And then it goes on because measures are reduced, and zero-covid never was a goal... would even go so far that some few countries pretty successfully did zero-covid strategies and stopped their virus, though sure, that is a pretty futile thing if the world is not "globally" doing this and you are likely not isolating forever/completely - so we just start to live with it.

> Was any variant successfully stopped with lockdowns?

Statstically speaking, almost surely yes: with millions of infections there are thousands of variants, every day. If somebody was prevented from infecting somebody with their variant (as patient 0) technically we stopped variants with lockdown. Maybe they more favorable for us, maybe they were more dangerous from us.

The mu variant, which caused a lot of worry, went away. It apparently escaped vaccines better than delta but spread much more slowly, so delta out-competed it. Perhaps if there were no restrictions it would have done better. Hard to say though.

It's true on an individual level too: someone who is very sick will stay at home, but someone with a mild head cold will still go out.

There's going to be a negative correlation between severity and something like "velocity" of infected persons.

Which begs the question of the long term utility and effect of symptom suppressing vaccines (that don't prevent transmission).

If a virus that would make make you very sick is contracted by someone who's vaccinated - They will now be in the 2nd category you describe ~'Sick, but not sick enough to stop them going out' -- They're now giving mobility to that virus that it would have otherwise not had (If they weren't vaccinated and were feeling too sick to go out and about)

So by usage of vaccines that only prevent severe symptoms, we pervert that normal negative feedback loop of virus spread and instead set the parameters to be more likely to propagate severe virus' that would usually keep you sick at home.

Vaccines don't suppress symptoms. They prevent symptoms by decreasing the viral load. They prevent transmission in the same way.

No, not _all_ transmission. Neither _all_ symptoms.

Or do lockdowns just prolong the inevitable?

Lockdowns are certainly a prolonging step.

But prolonging the inevitable is still useful, in that it slows down the number of hospitalizations on your march towards the inevitable.

Most hospital systems in the USA are stressed to severe levels. We had a nursing shortage before COVID19 even began, and the increased workload from COVID19 is clearly causing problems.

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Slowing things down gives more time for the old patients to leave the hospital, meaning doctors/nurses won't have to work as hard.

It's like the "invisible hand" or the "selfish gene" - just an analogy.

> Do you realise that mutation is not something the species can consciously control?

Very much so, and my post was carefully worded to refer to evolutionary selection pressure, and not any kind of agency on behalf of a virus.

I assumed the audience here would get it.

As an aside, there are much kinder ways to voice this kind of concern that don’t drip with contempt; consider taking a less accusatory tone in the future? That might trigger fewer downvotes the next time the reading comprehension module needs coffee.

It's not binary; if the virus is less infectious during incubation than during full infection, there's still selective pressure for milder symptoms.

A new variant need only replicate slightly faster to dominate (eventually).

Yeah I even said it would probably trend towards milder over time, just more slowly. That's definitely not a binary claim.

I think that the basic severity-lowering gradient still applies, but now it happens in two dimensions. Furthermore, it seems plausible that the sequence of variants "Original" -> Delta -> Omicron follows such a pattern.

First, evolutionary pressure will select for a lower dormancy period, i.e. a lower time to contagion. This is because a variant with a shorter dormancy will spread faster than one with a longer dormancy period if both are present in the same population. This is also exactly what happened with the Delta variant, which is asymptomatic generally for a shorter period[1] than the original variant, because it replicates faster.

Second, the usual process occurs for the usual reasons. This may be happening with Omicron.

[1]: https://www.health.govt.nz/our-work/diseases-and-conditions/...

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