Those results highlights a problem with the "vaccine efficacy" metric, which is that it decreases with exposure, even when exposure is the same for vaccinated and unvaccinated people. So the exact same vaccine will come out as more or less "effective" in different contexts.
Suppose that conditional on exposure the probability that a vaccinated person gets infected is 5% and that it's 50% for unvaccinated people. Now consider a group of 200 people, half of whom are vaccinated and the other half are not.
In that case, you would expect 50 people in the unvaccinated group and 5 people in the vaccinated group to get infected, which puts vaccine efficacy at (50 - 5) / 50 = 90%. Sounds pretty good!
Now suppose that everyone gets exposed twice. You expect 75 people in the unvaccinated group and 9.75 people in the vaccinated group to get infected, so vaccine efficacy is now (75 - 9.75) / 75 = 87%. It's lower than before, but in a sense, the vaccine worked just as well!
Moreover, exposure was the same in both groups by assumption, so it's not confounded by a difference in exposure between the groups. Even without confounding, as the frequency of exposure increases during the time period of the study, vaccine efficacy will come out as lower.
If you measure vaccine efficacy in a high-exposure environment, such as a prison, it's going to come out as very low, so the result of that study are not very surprising. In the long-run, we're all like those prisoners though, SARS-CoV-2 is coming for us, vaccinated or not.
(To be clear, it's better to be vaccinated when it comes for you, because it should still protect you against severe forms of the disease. It doesn't really matter if you're infected per se as long as it's benign.)
In a way, this makes sense, since there is a clear sense in which the vaccine *does* protect you less in a high-exposure environment, but I suspect that it's not how most people think about vaccine efficacy, which makes the metric a bit confusing communication-wise in my opinion.
In this case, a lot of people are inferring from this study that the vaccine is not as effective as we thought, but it doesn't really show that. It's just that what experts call "vaccine efficacy" isn't necessarily what ordinary people are really interested in.
I think the confusion this metric created is also responsible for the widespread sentiment that earlier claims of > 90% "vaccine efficacy" were misleading as more and more breakthrough cases started to be seen.
People were like: "What the fuck? You told me this thing was 95% effective and now there are reports of vaccinated people getting infected left and right? I want my money back!"
And I think it's mostly because the "vaccine efficacy" metric is confusing and people understandably didn't get that, as the frequency of exposure increases, the ability of the vaccine to prevent infection will go down. It's a failure of communication, one of many 🤷‍♂️
The bottom line is that "vaccine efficacy" is just a metric people came up with because they need *something* to quantitatively measure how effective vaccines are. This is not a problem per se, it's true that you need some metric to measure that!
The problem is that, if you don't explain what it really means, most people are going to infer that once you're vaccinated you only have a ~5% chance of getting infected no matter what they do and forever, but obviously that's not true.
By the way, as @ritwik_priya noted, this means that you can find "waning" even if there is no waning of vaccine efficacy *per exposure*. Some of the "waning" studies have found is probably just that.
See also those references on that phenomenon. This just illustrates a more general point, namely that vaccine efficacy is a complicated question, both conceptually and empirically. The discourse is doing a poor job at reflecting those complications.

• • •

Missing some Tweet in this thread? You can try to force a refresh
 

Keep Current with Philippe Lemoine

Philippe Lemoine Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

PDF

Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @phl43

23 Sep
Mdr, Mélenchon qui passe de la créolisation à Christine de Pisan, qu'est-ce que c'est que ce débat ?
Ça me fait rire de les entendre se vouvoyer alors que tout le monde sait très bien qu'ils sont copains comme cochons.
Il fout décidément cette histoire de créolisation à toutes les sauces. Il doit vraiment avoir envie de faire 6%.
Read 10 tweets
20 Sep
I think the conflict with China is stupid and I'd be glad if we stayed out of it, so I don't care that France was excluded from the regional security partnership between the US and Australia, what pisses me off is that this betrayal won't fundamentally affect our foreign policy.
That's why the French government's histrionics at the moment are so embarrassing. There is no point in putting on that show if, in the end, you just go back to business as usual, which is almost certainly what's going to happen. Draw some concrete lessons or shut the fuck up.
The truth is that we have aligned ourselves with the US against our interests time and time again and we're going to continue to do so even after our so-called allies have openly fucked us. I hope that I'm being too pessimistic about this, but I seriously doubt it.
Read 8 tweets
17 Sep
I must have missed the part where Russia pretended to be our ally, only to snatch a multi-billion dollars contract that was already signed from us and exclude us from the new regional security partnership that resulted from the steal, but it could also be that I have a brain 🤷‍♂️
People actually pay this guy, probably a lot, to explain international politics to them. No wonder we keep doing stupid shit when this is the kind of moron that passes as an "expert" these days.
Lmao, the sophisticates spent the entire Trump's presidency whining about how he was destroying the US relationship with your allies, but now Biden is openly fucking us and this guy is like "how come you didn't recall your ambassador under Orange Man Bad?"
Read 4 tweets
14 Sep
Milley's actions, which objectively border on treason, are cast in a heroic light in this piece, but this passage is pretty revealing about the kind of things he and his friends were *really* afraid of, even though I have no doubt they believe their own bullshit.
From day 1, the military has railroaded Trump into doing the opposite of what he'd pledged to do (greatly helped in that by Trump's own incompetence), effectively subverting the democratic will, but we're supposed to believe they're democracy's saviors 🙃 axios.com/off-the-rails-…
Every time Trump tried to withdraw using the normal channels, they have managed to railroad him (which again is partly Trump's fault but has happened to every other president so it's not just his incompetence), but Milley is shocked when Trump tries to do it behind his back 😂
Read 19 tweets
9 Sep
C'est encore pire que ça : non seulement cette affaire n'entraînera aucune conséquence négative pour Coulmont et Simon, mais vous pouvez être certain que la même chose ne sera pas vraie pour Mignot, qui sera à coup sûr ostracisé par ses collègues. C'est effectivement révoltant.
Cette histoire illustre parfaitement un phénomène très courant dans la recherche : il y a plein de gens dont tout le monde sait pertinemment qu'ils sont intellectuellement malhonnêtes, mais leurs collègues ne disent rien parce que faire des vagues est mauvais pour leur carrière.
C'est d'ailleurs la même chose quand je traite les épidémiologistes de l'Inserm et de l'Institut Pasteur d'escrocs parce qu'ils ne publient pas leur code et qu'ils pondent des trucs dont ils savent très bien qu'ils sont complètement pétés : "ça ne se fait pas" me dit-on.
Read 9 tweets
7 Sep
Has anyone ever considered genetically engineering SARS-CoV-2 to make it super-transmissible but harmless, while still having enough epitopes in common with the natural strains to confer immunity against them? It would effectively be a transmissible vaccine.
To be clear, I doubt we'd actually know how to make it super-transmissible and I can think of many reasons why this could backfire even if we did, it's just a random thought I had so I tweeted it, like I do with most of my random thoughts 🤷‍♂️
Looking forward to having my name in history books for having inspired the program that killed half of mankind by creating a super-transmissible virus that almost immediately mutated to also become super-virulent.
Read 6 tweets

Did Thread Reader help you today?

Support us! We are indie developers!


This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Too expensive? Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal Become our Patreon

Thank you for your support!

Follow Us on Twitter!

:(