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In this post Zvi doesn't try to forecast how many infections/cases/deaths there would be in the US without this new strain (unless I missed it... it is a long post). Yet he really should, because doing so will lead one to realize that the US is likely going to be at or close to herd immunity by ~May-June anyway, so a new transmissible strain that becomes dominant in the US around that same period can't plausibly make as huge of a difference as Zvi seems to be saying in this post.
Good Judgment's median estimate for "How many total cases of COVID-19 in the U.S. will be estimated as of 31 March 2021?" is ~130M currently. And Good Judgment's median estimate for "When will enough doses of FDA-approved COVID-19 vaccine(s) to inoculate 100 million people be distributed in the United States?" is ~May 1st currently. https://goodjudgment.io/covid/dashboard/
Assuming that 20% of vaccines go to people who had already been infected, this would mean that by May, approximately ~220M people (220M = ~140M + 0.8*100M) the US will be immune, or about 66% of the population. This could easily be higher or lower, but the point is that we're going to be at or close to herd immunity by the time Zvi says this new viral strain would start becoming dominant in the US.
In short, the news would be much worse if this new viral strain had spread to the degree that it has now several months ago. But in reality, I think we'll be at or close to herd immunity already by the time it becomes prominent, so it won't make that much of a difference.
EDIT: I misread Zvi's piece initially and mistakenly thought he wrote that that the new strain wouldn't become dominant in the US until May. I now see that he says "Instead of that being the final peak and things only improving after that, we now face a potential fourth wave, likely cresting between March and May, that could be sufficiently powerful to substantially overshoot herd immunity." Taking this view as true instead makes me see the new strain as significantly worse news: specifically, this two-month shift might be sufficient to make an additional ~10-15% of the population get infected/sick before herd immunity is reached. (I still think the post title is overblown, but still this is a significant update for me.)
I choose an operationalization for the second question in this comment: https://www.lesswrong.com/posts/CHtwDXy63BsLkQx4n/covid-12-24-we-re-f-ed-it-s-over?commentId=A38t5Ffxbm6GhpXuk
Some of my thoughts that lead me to think this are in my comments on this Metaculus question: https://pandemic.metaculus.com/questions/3988/how-many-total-deaths-in-the-us-will-be-directly-attributed-to-covid-19-in-2021/
IMO The title is overly dramatic and seems to claim that the news about the new strain is more significant than I actually think it is in terms of how much it should cause us to update our views of what infection risk and US COVID-19 deaths will be in 2021.
Operationalizing "There will be an additional distinct large wave of Covid-19 infections in the United States 2021" as "The 7-day average of new cases according to Worldometers will decrease by at least 33% from a previous value in 2021 and then later increase to at least 150% of the previous high", I'm forecasting 38%.
(EDIT: Update 12/28: I updated my forecast to 48% after realizing that I had my timing wrong on when the new strain might become dominant in the US. Previously I thought Zvi said something like 'not until May, or maybe June or July', but I now see he actually said "Instead of that being the final peak and things only improving after that, we now face a potential fourth wave, likely cresting between March and May, that could be sufficiently powerful to substantially overshoot herd immunity." If the new wave actually becomes dominant in March (or early April) (instead of May or later, as I mistakenly thought Zvi was saying before) and is as transmissible as it seems, that will probably be soon enough that there will still be enough not-immune people for there to be a significant surge in cases to cause the above forecasting question to resolve positively.)
This operationalization isn't that great because changes in numbers of tests could affect it a lot, but at least it's concrete.
Alternatively we could operationalize it in terms of the midpoint newly infected estimate at https://covid19-projections.com/ . Doing this and using the same 33% and 150% as above, I'd forecast 32%.
(For the Elicit question in the post, I went with the first operationalization and said 38% (EDIT 12/28: Now 48%.))
Thanks! On mobile I had to zoom in to reliably tap directly on the bar, which I didn't try originally.
FYI, I'm not actually forecasting 50% on the two Elicit questions at the end of the post. Tapping on the distributions caused me to unintentionally make forecasts on them. I was able to modify the forecasts, but saw no way to remove them, so just set them to 50% so as to hopefully mislead others as little as possible. (While I'd like to actually make forecasts on these questions, I think how they are operationalized matters a lot and yet I did not see any operationalization provided for them.)
How are these questions being operationalized?
Yes, updated the main post, thanks.