Wes Pegden Profile picture
15 Oct, 17 tweets, 4 min read
We have entered Phase II (or is it XXII?) of the COVID "discussion": gathering signatures for petitions.

In some sense it is the perfect phase for this moment, which involves remarkably little scientific curiosity or engagement.

Some thoughts. 1/17
First let's consider the GBD. This document lays out in concise terms the position that COVID mitigations should focus on vulnerable populations. 2/17

It advocates for the one of the most extreme (not a synonym for ridiculous) positions of this form, which is that "life as normal" should immediately resume for younger people.

My least favorite thing about the GBD...
...is that it does not do more to acknowledge the importance of balancing goals (such as not overwhelming healthcare resources), and that it seems uninterested in identifying any but the most basic measures (like handwashing) to reduce transmission in sustainable ways. 4/17

It is telling, I think, that many responses to this document focus not on it's content, which would not be considered radical without the context of the current political climate, but on theories about political influence. 5/17
One thing I cannot find in this document is a sentence which clearly misrepresents expert consensus on a scientific question. That is easy to do, on the other hand, for it's counterpart from the "other team", the "John Snow Memorandum". 6/17

For example, this document claims there is "no evidence" that previous infection from COVID confers lasting protection against future infection.

Experts have in the past had to push back on similar fear-mongering about reinfection from the media.

That will be harder now.

The authors also imply that strategies accounting for natural immunity would lead to a worse endemic stage for COVID.

(Why? Did the GBD propose to halt vaccine and treatment research? Or is the JSM arguing for ZeroCOVID?) 8/17

I do not know why a "war of signatures" can only be waged from extreme positions. In this case, the JSM argues not not just that we can't let our guard down, but that:
"Any pandemic management strategy relying upon immunity from natural infections for COVID-19 is flawed." 9/17
For example, this position would rule out one of the concrete suggestions from the GBD: prioritizing hiring nursing home workers who had previously been infected with COVID.

Why is "natural immunity" a dirty concept? 10/17
One thing the JSM definitely does not contain is an assessment of long term costs of mitigations and interventions.

Since they do not explicitly make a comparison between direct consequences from COVID and long-term consequences of containment efforts, 11/17
it is not clear whether the authors are confident that pursuing containment will prevent more COVID suffering and death than the general suffering and death pursuing containment may cause, or whether they think this question is irrelevant to the question of how to proceed.
Indeed, especially for unsustainable mitigations targeting younger populations, it is even possible for some measures to cause increases in COVID deaths. This phenomenon is not addressed in the document. 13/17

The other thing missing from this document (and all others advocating containment) is an appraisal of the likelihood of success in particular countries. The sum total of the feasibility argument provided is that it worked for countries like "Japan, Vietnam and New Zealand". 14/
I have been frequently surprised that highly educated people with domain-relevant expertise see these "arguments-by-analogy" as sufficient to demonstrate that places like the U.S. or Europe are likely to contain COVID.

We are betting lives on these analogies.

Strategic thinking involves the assessment of likely outcomes. When containment is pursued and fails we will have missed better options.

Most importantly, the pursuit of containment is not a logical or ethical consequence of valuing human life.

Finally, it's ironic this document bears John Snow's name. Snow was a pioneer of epidemiology who arrived at a radical data-driven insight and pursued the most targeted epidemic mitigation in history.

He was not familiar with the Swiss Cheese approach to pandemic management. /17

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More from @WesPegden

26 Sep
The attention-grabbing data shown in this Bloomberg article is data described as being collected from "1500 patients".


In fact, recruitment to this study was done via the social media post shown below.

The long-term burden of COVID infections is... 1/4
an important scientific question.

We are not making progress on this question by overemphasizing the role of anecdotes

There is no technical reason why this cannot be answered using a scientific approach. A random sample of past COVID+ patients should be surveyed... 2/4
and examined at 3 months, 6 months, etc, and proper comparisons should be made (e.g., to other respiratory infections).

We are 9 months into the pandemic.

The importance we place on this problem should be reflected in the seriousness with which we approach it. 3/4
Read 4 tweets
25 Sep
Age-targeted strategies are often interpreted in extreme ways: "cut off", "perfectly segregate", etc, some part of society, while everyone else "gets on with normal life".

Obviously in this formulation, skepticism is merited. Nothing is perfect, and "cutting" things off...1/9
sounds hard!

But this is an absolutist interpretation of ideas which should, like most, be interpreted quantitatively. The same misinterpretation could be given for all current strategies, by suggesting that masks, restrictions, etc., aim to "perfectly" stop all transmission. 2/
In fact, the goal of current strategies is to have a quantitative effect on transmission, reducing it for all groups essentially "as much as the market will bear".

In practice, this has involved implementing policies which begin harshly (lockdown), and gradually relax. 3/
Read 9 tweets
20 Sep
A quick note on this thread by @joel_c_miller before bedtime.

Joel is summarizing a nice argument coming from random graphs to suggest that increasing transmission rates among low-risk groups cannot be good, unless accompanied by other decreases. 🧵 1/9

This argument is valid if comparing two scenarios with constant transmissions. It is not valid if we expect (as I think we do!) that transmission patterns will eventually increase.

In particular, it is worth noting, that... 2/9
even in the simplest single-population models with time-varying transmission rates, epidemic sizes (and thus mortality) can be decreased by increases in transmission.[🤯]

Time dynamics make coupled systems complex, and intuitive reasoning about the effects of changes is tricky.
Read 12 tweets
17 Sep
In our paper w/ @ChikinaLab we
1) account for preferential mixing in age groups
2) do not require perfect isolation of at risk groups
3) do not assume that we can "turn off transmission" (indeed, we assume transmission gradually reverts to normal levels)1/
Joel is also concerned that aged-care facilities could support an epidemic (not localized outbreaks at individual centers) on their own without any involvement of younger individuals (staff/doctors/etc). 2/8

An earlier discussion on this ended abruptly:
I think its fair to say this is an unusual viewpoint.

Threads like this which dismiss age-targeted strategies out of hand inevitably work with the most simplistic and absolutist version of an idea. I have not seen an argument that we cannot have a quantitative... 3/8
Read 8 tweets
13 Sep
This commentary on herd immunity thresholds is making the rounds today. There is nothing new in this article, and parts of its commentary are quite misleading. It is worth thinking about why a commentary like this is widely shared by scientists.

I worry that the ways in which the article is misleading is, in fact, precisely why it is widely shared.

E.g., they sow doubt for infection controlled immunity, suggesting that "several rounds of re-infection" might be needed to generate robust immune responses. 2/
This is not a reasonable level of uncertainty to apply in an article that also discusses vaccine-induced herd immunity as an inevitable eventuality.

Although they explain some of the mechanisms which can lower HIT's, they also say misleading things, e.g. that HITs are only... 3/
Read 19 tweets
24 Aug
In light of the most credible reinfection case to date (👇) there has been discussion of what this means for herd immunity from infection or vaccines.

Quick thread with a simplified explanation of the basic concept of population immunity.🧵 1/8

What does it take for an epidemic to die out, so that a people are no longer being infected in significant numbers?

When first confronting this question, it might seem like the answer is that nearly everyone has to be protected from infection, so that any infected person is...2/
unlikely to infect anybody else.

However, it is not required that each infected person infects 0 new people for an epidemic to be unsustainable, we need only that each infected person infect less than 1 person on average, so that new infections are outnumbered by recoveries. 3/8
Read 8 tweets

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