Youyang Gu Profile picture
18 Feb, 12 tweets, 4 min read
I've seen many news articles cite that "the UK variant could be the dominant strain by March". This is emphasized by @CDCDirector.

While this will likely to be the case, this should not be an automatic cause for concern. Cases could still remain contained.

Here's how: 🧵
One of @CDCgov's own models has tracked the true decline in cases quite accurately thus far.

Their projection shows that the B.1.1.7 variant will become the dominant variant in March. But interestingly... there's no fourth wave. Cases simply level out:…
Just because a variant becomes the dominant strain does not automatically mean we will see a repeat of Fall 2020.

Let's look at UK and South Africa, where cases have been falling for the past month, in unison with the US (albeit with tougher restrictions):
Furthermore, the claim that the "variant is doubling every 10 days" is false. It's the *proportion of the variant* that is doubling every 10 days.

If overall prevalence drops during the studied time period, the true doubling time of the variant is actually much longer 10 days.
Simple example:

Day 0: 10 variant / 100 cases -> 10% variant
Day 10: 15 variant / 75 cases -> 20% variant
Day 20: 20 variant / 50 cases -> 40% variant

1) Proportion of variant doubles every 10 days
2) Doubling time of variant is actually 20 days
3) Total cases still drop by 50%
Given these facts, I think headlines along the lines of "CDC warns UK variant could be dominant strain by March" can be misleading.

It has the consequence of instilling fear in the public, who are much more likely to misinterpret it as "there will be another bad wave".
The amount of pessimism still present and being proliferated does not match a reality where:

1) Cases and hospitalizations have fallen by more than half in the past month (and still falling)
2) We have administered the vaccine to 40M+ people, with 1M new vaccinations per day
Of course, there's a very possible scenario that we'll see a fourth wave beginning in mid/late March and peaking in April/May. I'm not trying to downplay that.

But I'm baffled to see such a high level of confidence from the public health community that a fourth wave will happen.
I was told last year that the purpose of restrictions/interventions is to "flatten the curve". That the main goal is to make sure we do not overwhelm our healthcare system.

That messaging seems to have been shifted to "eliminate the curve". Why?
It's possible that selection bias may be at play (i.e. experts that are more confident about a fourth surge will have their voices amplified).

In any case, the future trajectory of the variant is still unclear, at least from the data. It's good to tread with cautious optimism.
Here's a great expert analysis @trvrb for what's next. It lays out the facts and expresses the uncertainties in the near term. The truth is not always headline-worthy.

Update: Here is a possible projection that shows a fourth wave in infections that peaks in April, but at a significantly lower level than the fall wave.

Obvious caveat that there is a high level of uncertainty.


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More from @youyanggu

17 Feb
Which metric is a better predictor of the severity of the fall surge in US states?

1) Margin of Democrat victory in Nov 2020 election
2) % infected through Sep 1, 2020

Can you guess which plot is which?
The left plot is based on the % infected through Sep 1, 2020. You can see that there is very little correlation with the % infected since Sep 1.

However, there is a *strong* correlation when using the margin of Biden's victory (right).

Infections % from
This is the strongest single variable I've seen in being able to explain the severity of this most recent wave in each state.

Not past infections / existing immunity, population density, racial makeup, latitude / weather / humidity, etc.

But political lean.
Read 15 tweets
17 Feb
Tue Feb 16 Weekly Vaccination Update:

Not much changed over the past week. New vaccinations has been stuck at 900k-1M per day for the past *month*.

New doses distributed remains low, but hopefully this changes soon with the newly announced allocations.…
We renamed our page from "Path to Herd Immunity" to "Path to Normality". Reasons explained in our thread from last week:

More encouraging news: more people are getting their second shot daily than the peak daily infection rate in December.

The number of new vaccinations is now 4x the number of new infections. Hopefully this pattern continues.
Read 4 tweets
11 Feb
The recent focus on reaching herd immunity through vaccination may be overblown.

My modeling suggests that it is increasingly unlikely that the US will reach the immunity levels required for theoretical herd immunity in 2021.…

(A 🧵 w/ my thoughts)
This conclusion is based on the following new developments over the past month:

- Remained high levels of vaccine hesitancy
- New variants that may lower vaccine efficacy
- Rollout of the J&J vaccine (efficacy ~70%)
- Delayed arrival of the children vaccine
That said, herd immunity does not have a hard threshold, and being close to herd immunity may be sufficient to prevent large outbreaks.

Our goal should not be to reach "herd immunity", but to reduce COVID-19 deaths & hospitalizations so that life can return to normal.
Read 12 tweets
10 Feb
Wed Feb 10 Weekly Vaccination Update:

New vaccinations has been stuck at 900k-1M per day for the past three weeks, while second doses have nearly tripled.

New doses distributed remains stubbornly low, so this pattern may continue...…
This seems to confirm analysis announced by White House Data Director @cyrusshahpar46 that shows that the majority of delivered first doses have already been administered.

The bottleneck is supply.

California is now vaccinating at 4x the rate of new infections, a tremendously improvement over January.

Florida took a different route but with has equally impressive results thus far. Their rate of new 2nd doses is among the fastest in the country.

No politics, just data.
Read 6 tweets
3 Feb
Wed Feb 3 Weekly Vaccination Update:

It was a disappointing week. New vaccinations decreased compared to last week.

This is also the first week where fewer doses were distributed than administered.…
1st doses remained under 1M/day while 2nd doses were up 60% compared to last week (236k -> 381k a day).

The clear pattern that is emerging is that states are allocating their limited doses to give out as 2nd doses rather than to vaccinate new people.
Given that the pace of "doses distributed" have also not increased since early January, the outlook is worrisome.

Unless the pace of new distributed doses increases, it currently looks like we may be at a plateau in new vaccinations for a while.
Read 7 tweets
27 Jan
Wed Jan 27 Weekly Vaccination Update:

Given no unforeseen supply issues, we estimate that the general public can receive the vaccine by April.

We also estimate over 60% of the US adult population will be fully vaccinated by June.…
These estimates are driven by data. In the past week, over 1 million doses were administered per day, a 20% week-over-week increase.

While there are news reports of anecdotal supply issues, this has not shown up in the data. If this changes, we will update accordingly.
Nationwide, new infections are decreasing quickly while vaccinations are steadily increasing.

But around 500k people are still being infected per day, double the summer peak.

The drop in infections is more likely due to a post-holiday slowdown rather than vaccinations.
Read 6 tweets

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