Agreed. Omicron is going to be the vaccine for Delta for those misinformed enough to not get the actual vaccine.
And it’s good to make the point about virulence, because too many people seem to mistake a tendency for lower virulence for some certain cast iron future. It doesn’t work like that. Especially not for a virus with currently a low fatality rate.
If there’s a positive, it’s that virology is likely to be a popular and well funded area of study for at least a few years.
Omicron is basically the viruses response go the billions of vaccinated person it’s had to face for months.
What do you mean by this? Because the virus has a low fatality rate, it must go higher? Like it’s a roll of the dice or something? I don’t know that to be true. There are billions of viruses out there, don’t almost all of them have low fatality rates?
Chronos explained it better than me, but basically, because the fatality rate of the virus is already quite low, there is little selective pressure for the virus to become less virulent.
Or, put it this way: I think that all of the successful variants of Covid-19 have been more virulent than the initial Wuhan strain.
So, while it is indeed true that in the long term we would expect milder variants to win out, that’s no guarantee that on shorter timescales the virus cannot either remain at a stable level of virulence or even some more deadly strains might happen to have features that make them more successful despite killing off more of their hosts.
I don’t agree with this. One factor is that fatal Covid patients don’t die until they can no longer infect other people anyway. So by that theory the fatality rate could be much higher without providing selective pressure, since until the virus is able to go back for Round 2 on an individual, it’s already spread as much as it can, and it can do no more with the host.
The reason evolution would go away from ability to kill is that ability to kill is inefficient. The features that enable ability to kill cost resources to the virus without providing any value. A small organization isn’t going to retain inefficiency over time. Once the virus is established, it’s competing with versions of itself. Variants that aren’t wasting resources on ability to kill are more efficient.
In early days, it’s likely more beneficial for the virus to be hardier, more lethal, since it is competing with a billion different baby viruses and needs to survive that. The game changes once the virus is established.
People don’t have to die. As long as hospitals are being stressed and it gets a lot of news coverage, there could be selective pressure on this virus.
Covid-19 has already become more virulent a couple of times, so I don’t know why it would be so contentious to say that that might happen again.
Once again, in the long term, yes, evolution will favor variants which don’t kill. However, in the short term, all bets are off. This is because of two factors which you haven’t included in your analysis
A mutation might have more than one effect. So it may have an effect that greatly aids the virus in spreading, but also happens to make it more deadly as a side effect.
Viruses are constantly mutating, so any given variant will have a bunch of mutations. In a successful variant some mutations will of course be beneficial but there may also be several neutral and even detrimental ones. As long as the benefits outweigh the losses, it can spread. Over time evolution will weed out the bad genes. But again, over time.
Note that of course there have been viruses that have infected humans and been deadly for a very, very long time. Viruses are not obliged to become benign overnight. Smallpox certainly didn’t get the memo.
As far as I know, there’s no evidence for this. The successive variants have had a higher transmissibility. There was speculation that they were more virulent but I don’t there was any evidence for that.
The data for alpha and beta being more virulent is still debated (though it is still there, see my second cite below).
Delta seems the most clear, as it does result in a higher viral load and several studies comparing hospitalization rates for different forms of the virus example1, example2 have found it to be more deadly.
Yeah, you’re right. I just found some papers that suggest that delta does result in a higher hospitalization rate per case. Not just total hospitalizations. https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(21)00475-8/fulltext
Does anyone know any good sources on the larger question of changing virulence over time? I’ve heard of the idea, but it also seems to me like whole populations can gain some immunity–not enough to squelch the disease entirely, but enough that it doesn’t kill as many after a while. But then when those people bring the disease to an isolated population, the new people start dying. So how often is it really the virus that’s mellowing out, vs. us adapting?
Can’t answer that for you but I do what to say I really like the question and await the answer with you.
I doubt you’ll get a clear cut answer though.
It would be good if we could solve the protein folding and assorted other problems*, and work out in a lab how virulent a virus (or variant) is.
But we haven’t and in the meantime all the data is inferred out of messy real world case data. Even with the alpha and beta variants of covid the data is still debatable and it’s hard to imagine a situation where we’d have more case data.
* AIUI the protein folding problem has been a little overhyped, in that it’s a (hella) useful tool that will enable progress in many applications but won’t overnight solve all those applications. Figuring out what effect a virus will have on a human body is a good example of an application that would need a lot of progress in other areas (crucially our understanding of the immune system).
This line of thinking doesn’t really work. Viruses neither need nor have resources. They have no tissue, no cells, no metabolism, no reproduction. Technically they aren’t even alive. A virus is just a chain email between host cells, and all it says is “copy this and send it to your friends until you die”.
Opportunity can be thought of as a resource. Other non-concrete things too. Like time, for instance.
Viruses don’t have their own resources besides genome, some kind of coating, and maybe an enzyme or two. This makes it that much more reliant on cellular resources.
A virus doesn’t have to be super deadly to evolve into something less virulent. If it causes enough illness to change people’s behavior, a less virulent virus may be selected.
Let’s say you have two variants with equal transmissibility, but one is more virulent than the other. As hospitals start to fill up, people start staying home (either through mandates or self-regulation). The more virulent variant will lose opportunities to replicate while the mild virus continues to infect the population. Eventually, the mild virus takes over.
Right, I was responding to the flawed assumption that a virus expends more resources by being more virulent. Mainly because viruses have no such resources to expend, but also because virulence is a function of physical properties that require no resources to maintain.
Even if you accept this definition, the idea still doesn’t work. The factors that make a virus more virulent (mainly protein folding) are not sustained by investments in time or opportunity.
On the issue of virus becoming less/more deadly, I thought the leading hypothesis for why the Spanish flu pandemic was so bad, while later outbreaks weren’t (for instance in 2009) was a variation on this?
As the pandemic hit during the 1918 fighting season in WW1, soldiers who got mild cases stayed in the trenches and those who got severe ones were sent to the rear, ie into the general population The virus therefore had selective pressure to become more severe?
Firstly, I think it would be a very difficult hypothesis to verify.
As we have seen, there are many unknowns with just the immune system itself, let alone in the interaction between the immune system and various strains of a virus while taking into account population movement and socioeconomic factors etc.
There are many potential reasons why Spanish flu was so virulent in the first place, and why it got so much worse in the second wave.
But the second thing to appreciate is, it doesn’t need a special explanation.
What I have been trying to say is that the factoid “Viruses trend towards less virulence” is true as a generalization in the long term.
It doesn’t at all preclude a more virulent strain happening to have characteristics that make it more fit overall than extant variants. As we saw with the delta variant.
Impossible I would think. But, there has to be some reason why the 2009-2010 outbreak was so mild.