That IS a big deal! Well done!! 
I saw this expressed in the YouTube comments - that the vaccine might only make the vaccine stronger. If this were a Zombie movie, it would mean the heroes would let themselves be eaten - because fighting the zombies would only make them stronger? (BRAINS!!! 
) (and I am delighted to learn that Discourse has zombie emojii).
@dsterncardinale I just watched your Delta Variant video. It was not what I was expecting. I was hoping for an analysis of the mutations and how the mutations arose and promoted viral fitness or transmissibility in some way.
At the end you said that the delta variant is āa result of widespread vaccination.ā I do not see the evidence for that statement. Would you please explain how you came to that conclusion? The delta variant arose in India before the country had widespread access to vaccines. Likewise, other variants arose in the UK, South Africa and Brazil prior to vaccines being available. My assumption was that these variants arise due to uncontrolled infection rates (for example in Brazil social distancing measures and masking were being discouraged by the President, leading to a massive outbreak in which it was assumed the majority of people in some cities could have been exposed to the virus). I have been seeing anti-vax propaganda now stating that vaccines are making the pandemic worse, so I think that concluding that vaccines caused the delta variant could be a dangerous idea to spread, unless there is good evidence for that fact and how we should respond. Iād appreciate your thoughts. Thanks!
Widespread vaccination (leading to robust immunity in a large % of the population) creates the selective pressures that favor the delta variant - high viral load, preferentially infect the nose rather than lungs, etc. That and many other variants have appeared over the course of the pandemic, with varying degrees of success, but under the current conditions, delta seems to be the most fit. Thatās because weāre making it harder for the viruses to spread by limiting the available targets, so this set of phenotypes is best right now. And in terms of the long-term trajectory of the pandemic, that indicates weāre winning - even if we donāt hit herd immunity, because the selective pressures imposed by very strong inter-host competition will very likely drive a decrease in virulence.
I do hope I covered why delta is so transmissible, but I felt like digging into the specific mutations wasnāt particularly important.
I understand the rationale behind the argument you are making (in terms of the idea about selective pressures) but where does the data come to support that ādelta is a result of widespread vaccination?ā Delta arose in India before vaccines were widely available there and has become predominant around the world because it is so infectious. While there are breakthrough infections here in the US, delta is spreading rapidly among the unvaccinated, with the highest case rates in the states and counties with the lowest vaccination rates.
I would follow your reasoning if delta arose in New England or in Israel where and when vaccinations rates have become high, but that is not what happened. Is it hypothesized that delta arose in a heavily vaccinated community in India? I thought vaccines were very hard to get in India when delta arose.
Let me ask also, is their any evidence that Delta is more dangerous, except that it might be resistant to the vaccine?
If not, then perhaps its rise is not actually detrimental to those who have not been vaccinated.
The conditions that favor delta are the result of widespread vaccination. If the population was still largely naive, other variants would be winning. Thatās all. Whether it originated among highly vaccinated populations isnāt important - high vaccination levels have imposed selection that favors delta.
And I want to emphasize again, this is a good thing. This is what vaccination does. Itās evidence that what weāre doing is working - weāre making life harder for the virus.
@swamidass as far as I know right now, the mortality rate among unvaccinated associated with delta is not any higher than previous variants.
I think the jury is still out on whether Delta is more virulent, making people more sick. Iāve been reading reports about more pediatric cases in hospitals, including with COVID lung (not just MIS), but I donāt think there is enough data analyzed yet to know for sure. Iāve also heard a couple reports now of people who had a mild infection with Alpha, deciding not to get vaccinated with the assumption that they were protected with acquired immunity, but now getting much more sick with Delta.
Can you link to some of the evidence that suggests this? I have not seen this idea discussed elsewhere.
Why is that the case? Since Delta is so contagious, wouldnāt it win against all other variants regardless of the level of vaccination in the community? Isnāt Delta the predominant strain even where vaccines are still not very accessible?
Edited to add:
And based on the actual epidemiology, isnāt it more likely that Delta arose where there had been prior widespread infection? So Delta arose and spread while avoiding selective pressure from the immune responses to prior variants (like Alpha). So I wouldnāt peg Deltaās spread on the vaccine so much as pre-exposure/immunity to other variants, even from natural infection.
@davecarlson @Michelle I know itās long, but I went through the underlying evolutionary dynamics in that video linked above.
The short version is that in naive populations, the rate-limiting step in the viral life cycle is how well it competes to be the predominant variant within a single host, in competition with all the other viruses in that host. This is intrahost competition, which imposes selection for greater competitiveness and tends to (not always, but tends to) lead to selection for higher virulence.
But late in a pandemic, or once a large % of the population is vaccinated, the rate-limiting step is transmitting from the current host to a new host, and the viruses within one host are primarily competing with the viruses within other infected hosts to spread to the relatively few remaining susceptible hosts in the population. This is interhost competition, and it imposes selection for greater transmissibility, often (not always, but often) at the expense of intrahost competitiveness, and therefore virulence.
So even with fairly high infection rates (think like NYC area), youāre only hitting, what, like 30% of the population has some degree of protection? And thatās not protective antibodies actually present, just the memory cells required to make them. So new hosts arenāt actually in super short supply prior to vaccination, and intrahost competition still predominates. To be sure, the balance will shift towards transmission as more people are infected, but not nearly to the degree imposed by widespread vaccination.
That would depend on how well it competes within individual hosts. Competitiveness is going to be based on things like attachment rate, adsorption rate, burst time, burst size, so itās going to be a phenotype under selection (which means virulence is also under selection, less directly). If there are a ton of hosts available, then you need to be pretty good at intrahost competition to be successful. Delta may be just as competitive, but more transmissible because it is more concentrated in the nose. Or it maybe be less competitive in some way, which facilitates more opportunities for transmission. A lot of places arenāt seeing big Delta outbreaks yet (as of the latest update on Covariants), but probably will soon, and that might tell us something.
This isnāt really being discussed, at least not that Iāve seen, so I donāt have anything specific to link. This is just me applying the evolutionary dynamics of pandemics to this specific pandemic.
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