15 Oct, 9 tweets, 2 min read
Something that I think is worth explaining:

The term "herd immunity" has a few different meanings, all of which are quite precise. This is an important point
In a very strict mathematical sense, herd immunity is the slowing of disease spread due to sufficient infected people in a population (such that Rt<1)
This leads to the second definition, which is the ability to calculate immunity within a population based on dynamics of disease spread
And finally, the common usage that's being bandied around a lot these days - herd immunity to describe a population which is largely immune to outbreaks of an infectious disease due to existing population immunity
Problem is, all three of these are being combined into a single idea in the popular media, which is not great because only definition 3 results in a somewhat permanent ending to the pandemic
The #GreatBarringtonDeclaration, for example, uses the first definition in a very disingenuous way to imply that endemic transmission of the disease (where Rt may at some points be <1) is equivalent to population immunity that prevents outbreaks
If someone uses the term "herd immunity" to describe an actual strategy or outcome from COVID-19, it's worth digging in to EXACTLY what they mean by that term, because often it's very much not what you'd imagine

Also, I made an error in the second tweet - in a strict mathematical sense, herd immunity is having sufficient people IMMUNE to the disease in a population. Infection does not always confer immunity, and you can be immune without infection (vaccines!)

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More from @GidMK

14 Oct
John Ioannidis, of "Most Published Research Findings Are False" fame, has now had his paper on IFR published

Let's do one, final, twitter peer-review on the study 1/n
3/n I should say at the outset here - the only personal comment I would like to make about Professor Ioannidis is that he is a very smart man who I respect tremendously

I will, however, examine the paper, because I think that is what science is all about
13 Oct
Imagine if someone was to say "COVID-19 hasn't caused most businesses to close, they were all doing badly anyway"
"Lots of businesses close every year, how do we know that they didn't just close WITH COVID-19 rather than FROM it?"
"All this economic impact is overblown. My friend's cousin's third ex-wife lost her business, but it was in the red anyway"
12 Oct
Have lockdowns been bad for the economy?

A new report from the International Monetary Fund has a very interesting answer to the question 1/n
2/n The report is here, and well worth reading. At the outset I should say that ALL OF THIS EVIDENCE IS UNCERTAIN

The IMF is great, and has tried very hard to be accurate, but it is important to take care when reading these findings imf.org/en/Publication…
3/n The basic summation is simple:

- lockdowns probably cause economic harm
- large outbreaks of COVID-19 also cause harm
- it is hard to disentangle this complexity
- there are almost certainly situations in which lockdowns are beneficial to the economy
12 Oct
Recently, John Ioannidis, of "Most Published Research Findings Are False" fame, published a commentary piece on COVID-19 and global action

I thought it would be good to do a bit of peer-review on twitter 1/n
2/n You can find the paper here - it is a classic commentary piece, which means it is mostly the perspective of the author: onlinelibrary.wiley.com/doi/10.1111/ec…
3/n Given the author's very strong public stance since early March, it is perhaps unsurprising that the main message of the piece appears to be that COVID-19 is not very bad but government actions are
10 Oct
It's fascinating what turns out to work in terms of helping people if you ignore empty moralizations about what we should and shouldn't do

This is but one example
For example, there's good evidence that an effective treatment for heroin abuse disorder is prescription (safe) heroin

bmj.com/content/327/74…
Safe injecting spaces - while counter-intuitive because you're assisting people in taking drugs - are arguably the most effective way to reduce the harms of some illegal drugs

ncbi.nlm.nih.gov/pmc/articles/P…
8 Oct
Apparently, there is a fly on Pence's head

I am not watching the debate
Every person in the U.S. simultaneously googles "Is fly on head a sign of COVID-19?"
Oh hey look