Intellectual reply required

[time2tork]

I know this sounds a bit silly.

But I'm genuinely asking.

What happens to the Delta coronavirus now we have Omicron?

Because wasn't there a strain before Delta but we never hear of it now?

And now omicron is spreading we are hearing less of delta?

So where do they go?
Do the previous strains naturally end?

They naturally end...or die out. Theoretically, places that don't have omicron will continue to have delta as the dominant variant. For example, in Peru, delta was late in arriving and i think something like lambda or kappa was the dominant variant for quite some time: this worked out not so well for Peru as this variant was more lethal (but not more transmissible) than delta.

I would imagine thousands of niche strains of SaRS-CoV-2 have already died out and they haven't been missed. Delta may well be stored in some sort of virus repository for future study (I believe several strains of Spanish flu are still under storage somewhere in the US I think, for example).

I'm also interested in understanding the science behind this more. (My scientific knowledge is sadly very limited.)

I know that a new variant, if more transmissible, can become the dominant one, but I don't really understand how this works and why the two don't continue to co-exist alongside each other? Is it because more people build up immunity from the transmissible variant so that there are fewer people available to be infected with the earlier variant? It doesn't quite compute in my head...

Effectively Omicron out competes the other variants as it is more infectious that is of course until a more infectious variant comes along and out competes Omicron.

The flu variants that caused the 1947 and 1968 flu pandemics that together caused more deaths than Covid are still in circulation it's just that they have been out competed by more recent variants so that they are very rare.

Interestingly the current flu jab was originally developed in response to the 1968 pandemic but by the time it was developed, tested and approved for release most people had already developed natural resistance. So they tweak it every year in response to the previous year's variants. Sometimes they miss a new variant like in 2017 that then causes a high flu death toll one winter.

@1dayatatime

Effectively Omicron out competes the other variants as it is more infectious that is of course until a more infectious variant comes along and out competes Omicron.

The flu variants that caused the 1947 and 1968 flu pandemics that together caused more deaths than Covid are still in circulation it's just that they have been out competed by more recent variants so that they are very rare.

Interestingly the current flu jab was originally developed in response to the 1968 pandemic but by the time it was developed, tested and approved for release most people had already developed natural resistance. So they tweak it every year in response to the previous year's variants. Sometimes they miss a new variant like in 2017 that then causes a high flu death toll one winter.

This is basically how much of biology and evolution works. Its called natural selection (or sometimes survival of the fittest). The key to understanding this is that genetic fitness has nothing to do with biological fitness. Genetic fitness merely describes the capacity to reproduce. Much of the time this genetic fitness may actually come with other vulnerabilities.

As it transpires, omicron seems to be genetically fitter than delta, hence it will likely ultimately out-compete delta. Whether it has additional vulnerabilities is harder to say at the moment. So far, symptoms seem a bit less severe.

This is the key to understanding most of biology really, from why we have so many different species of birds, to why highly targeted cancer therapies often ultimately fail.

Thank you for the explanations. I'm probably being thick but I still don't totally understand how it out-competes Delta.

I still don't understand why they don't keep spreading concurrently. So, if person A has Delta, they might pass it to person B. Meanwhile, person C has omicron and passes it to persons D, E and F because it's more transmissible. But person B still has Delta, and might presumably pass it on to person G, who might then pass it to person H etc? So Delta is still spreading, even though omicron is spreading faster. So what happens to Delta in the end? Does it fizzle out because so many people have already had omicron and have therefore developed immunity? So that, person H perhaps doesn't spread it to anyone? If that's the case, though, I still don't really understand it because having covid once doesn't seem to stop people from getting re-infected. So how does it work?

Sorry, please be patient! I'm trying to understand!!

@AlexaShutUp That is a question very well asked.

Imagine you have 2 house burglars. One has a skeleton key that is tailor made to the front door of your house. The other has a key to the back door, but it is a bit fiddly and takes a bit longer to get in.

Burglar One is a bit quicker on foot (more transmissable) so gets to your house first. Burglar 1 has control of your house. He goes round and leaves the key in the back door so it cannot be opened by a key from outside.

Burglar 2 arrives a bit later. He tries his key to your back door, but he can't get in.

Burglar 1 then decides to target your next door neighbour (infect the next person). Again, he arrives more quickly and gets in to their house more efficiently. Burglar 2 has the same idea, but when he arrives, he has the same problem.

This breaks the chain for Burglar 2, who is slower and less efficient at getting in houses than Burglar 2.

Not a perfect anaology but does that make sense?

Yes, thank you @Lex345, that does actually make sense. Good analogy!

No problem 😊

@AlexaShutUp

Thank you for the explanations. I'm probably being thick but I still don't totally understand how it out-competes Delta.

I still don't understand why they don't keep spreading concurrently. So, if person A has Delta, they might pass it to person B. Meanwhile, person C has omicron and passes it to persons D, E and F because it's more transmissible. But person B still has Delta, and might presumably pass it on to person G, who might then pass it to person H etc? So Delta is still spreading, even though omicron is spreading faster. So what happens to Delta in the end? Does it fizzle out because so many people have already had omicron and have therefore developed immunity? So that, person H perhaps doesn't spread it to anyone? If that's the case, though, I still don't really understand it because having covid once doesn't seem to stop people from getting re-infected. So how does it work?

Sorry, please be patient! I'm trying to understand!!

They do keep spreading concurrently for a bit. For example it took about 8-10 weeks for delta to become the dominant variant in Germany (where I live). Basically, the effects you describe above happen to the point that the more transmissible variant suppresses the less transmissible variant. If you think about it, in the model you describe (ie a person with delta consistently infects an additional 1-2 people and a person with omicron infects 3 or maybe more, you eventually end up with omicron dominating).

Mathematically this effect can be demonstrated as follows based on the assumptions provided above

Delta: 1.51.51.51.5 = about five cases for four rounds of infection
Omicron: 3333 = about 81 cases for four rounds of infection