It depends on the R0 of the mutation, and the efficacy of the vaccine.
For instance if Delta has an R0 of 8, and we're 100% vaccinated, and the vaccine has an efficacy of 85% against infection, the resultant Rt would be 1.2:
8 * (1 - (1 * 0.85))
So that means that some other form of mitigation on top of 100% vaccination would be necessary to stop the spread.
But for mutations with lower R0, or higher vaccine efficacy, herd immunity may still be possible.
That's kind of a moot point since the Delta variant has now out competed all other variants in the wild. If another new variant takes over from Delta it's unlikely to have a lower R0. At this point nothing we do can really stop the spread. Everyone should get vaccinated if they can because herd immunity won't protect anyone from infection.
> At this point nothing we do can really stop the spread. Everyone should get vaccinated if they can because herd immunity won't protect anyone from infection.
I think that's an overstatement of the links you are sharing.
Several parts of the country have pushed Rt < 1, so there are clearly things we can do to stop the spread, through a combination of vaccination and other mitigation measures.
And the definition of herd immunity is literally what protects people from infection. (Herd immunity includes vaccine immunity.) And even before the HIT, vaccination reduces contagion, reduces the doubling rate, buys time to implement further mitigation to drive down Rt < 1, and saves lives.
Anyway, what the Astra Zeneca guy is saying is just that our vaccines are not effective enough against infection to get Rt < 1 on their own.
mRNA Vaccines do have efficacy against infection, and additional effectiveness against infecting others; it's just that they're still not quite as effective as their effectiveness against hospitalization and death.
Improved vaccines, or the third-shots happening now (which do temporarily improve infection efficacy) improve those stats. Herd immunity isn't yet theoretically impossible even if it's a practical impossibility in our populations.
It probably is true that we can't go back to the way we were pre-covid, no distancing, no masks, and avoid COVID spread. We're not there and may never be since there's a likelihood that some variant of COVID will be endemic.
But there's plenty we can do - vaccination, and mitigation to get Rt < 1 during spikes. Those two practices protect people from infection.
Wait are you seriously saying masks, lockdowns, etc. during spikes _forever_? “The covid season is upon us, let’s stock up on masks, pull kids out of school, and cancel our overseas trip”? For the foreseeable future?
The point is Rt. If Rt is above 1, and the disease has a degree of mortality similar to what it has now, then it means the case count will double at some rate. And ICUs will fill up, and people will start dying from things like broken legs and pneumonia from not being able to get sufficient care. Does that make sense? That's just what Rt > 1 means; case counts are doubling. If Rt is above 1, then if you don't want the disease to eat the world, something needs to happen to get Rt back below 1. If not, it will happen naturally, solely through natural immunity and unnecessary death.
So the goal simply needs to be to keep Rt below 1, or to knock it back below 1 before prevalance becomes dangerous and threatens ICUs.
But that doesn't necessarily mean lockdowns. If there's a spike but already a good level of immunity, it might just mean masks on public transportation for a couple of months, or people naturally choosing to go out to eat three fewer times a month, or whatever.
The measure of required mitigation depends entirely upon the circumstance in the moment. If Rt spikes a little, you don't need to do much. If it spikes a lot, you need to do more. But with enough vaccination, we might not ever need full lockdowns for covid again.
> For instance if Delta has an R0 of 8, and we're 100% vaccinated, and the vaccine has an efficacy of 85% against infection, the resultant Rt would be 1.2:
For herd immunity, you also need to take into account that infected people—even symptomatic ones—are less infectious to others, if they're vaccinated.
Yeah, I'm familiar with that - I think that can be bundled into the efficacy number if you look at it as "efficacy against infecting others".
Last I heard, the CDC gave a 95% CI of the mRNA vaccines being 26% - 84% against infection (from Delta), and there's an additional 40% - 60% protection against infecting others (I've seen that estimate in multiple places but I don't know the source). If that's true, it suggests an overall range of 55.6 - 93.6 effectiveness against infecting others.
For instance if Delta has an R0 of 8, and we're 100% vaccinated, and the vaccine has an efficacy of 85% against infection, the resultant Rt would be 1.2:
8 * (1 - (1 * 0.85))
So that means that some other form of mitigation on top of 100% vaccination would be necessary to stop the spread.
But for mutations with lower R0, or higher vaccine efficacy, herd immunity may still be possible.