Dr Ellie Murray, ScD Profile picture
Oct 1, 2021 28 tweets 8 min read Read on X
Everyone keeps talking about covid becoming endemic, but as I listen to the conversation, it’s becoming more & more clear to me that very few of you know what “endemic” means.

So here’s a thread on how pandemics end.
In the beginning of any pandemic, we have 4 options for what could happen:

1) continually occurring disease, with small or large surges
2) local elimination of disease
3) global eradication of disease
4) complete extinction of the pathogen
Option 4 (extinction) is absolutely the hardest, but long-term would mean we could all completely forget about the disease.

We have basically never done this in the entire history of humans—but, if we’re being honest, a big reason we haven’t is fear & mistrust of other humans.
Option 3 (eradication) is also very hard but long-term just about everyone could forget about the disease.

You & I aren’t worried about smallpox, no matter where we travel or what we do — unless you’re a researcher at one of the 2 super high biosecurity labs that have a sample.
Option 2 (elimination) is still pretty hard, and long-term not everyone can forget about the disease.

For lots of the world, this is measles is — we’ve got great vaccines & most of us don’t need to worry about measles, but public health officials still monitor for it everywhere.
Now we get to Option 1 (continually occurring disease). This is easier short-term but it’s the hardest *long-term*.

It’s also super vague: it could mean anything from hundreds or thousands per day to one or two per year.

The other name for this is, you guessed it, “endemic”.
In more technical terms “endemic” means: “Controlled at or below an ‘acceptable’ level”

What level is “acceptable” differs from place to place, over time & between diseases, and it may not always be explicit, but when a disease is endemic, there is a threshold!
If a disease is really bad, ‘acceptable’ is very low—potentially even indistinguishable from elimination.

The plague (yes that one!) is kinda common among rodents in parts of the US, but if even ONE person shows up to a doctor with symptoms, public health jumps into action!
On the other hand, if a disease is not really that bad at all, the acceptable level can be really very high.

Up to 80% of US adults are infected by the virus that causes cold sores (aka oral herpes)!

But public health takes *nearly* no action, except to protect infants.
You might have noticed something important here, and it’s something I think MANY of the people shrugging off covid becoming endemic get wrong:

“Endemic” does NOT mean “harmless”.
Whether a disease is endemic, epidemic, eliminated, or eradicated does NOT tell us how serious it is, and does NOT tell us how many people get sick or die.

We have to CHOOSE that number.
So here’s the kicker: “endemic” doesn’t mean “never think about covid again”. It’s exactly the opposite!

Endemic means someone is ALWAYS thinking about covid.

Endemic means public health is always monitoring disease & always intervening when cases cross the “acceptable” level.
Every time I tweet about this I get people in mentions saying “but we don’t take precautions for the flu!”

Those people are 100% WRONG!

Thousands of people work daily to monitor, prepare for, & respond to fluctuations in flu number and in the flu virus itself! It’s a HUGE task!
Sure, maybe the flu doesnt impact *your* life, except some years you get a flu shot, or maybe you have once or twice really actually gotten the flu & not just a bad cold you *called* the flu.

(Pro-tip: if you dont feel like you’ve been hit by a train, it’s probably not the flu).

There are clearly defined “acceptable” levels for different strains of the flu, and we spend so so much time & energy & money working to keep the flu below those levels. So that YOU don’t get sick.
When flu cases cross the threshold & the public health lever switches from “monitor flu activity” to “take action YOU don’t notice.

But not because it isnt happening — because the acceptable level is LOW ENOUGH that those actions happen before it impacts your daily life.
If you work somewhere like a daycare, or a nursing home, or (like me) a School of Public Health that shares a campus with a hospital, you probably DO sometimes notice.

Because those are places where flu is most problematic & so they are also where we focus our interventions.
So what does this tell us about how pandemics end?

Well, it tells us that we CAN put in the work to really get rid of it once & for all, if we have the will and the strength and the interest and the resources.

It probably gets harder & harder the longer we wait, though.
Smallpox was around for a very long time before we took action & it took a long time to defeat.

Similarly, polio eradication is long overdue, but we’re still trying and I’m certain we will get there.
Yes, eradication is HARD but we could still choose to make it our moonshot if we wanted to.

It would definitely take time. It would probably take new science, new ideas, & new tools. And it would take both leaders & everyday people actively committing to doing what it takes.
Realistically, despite New Zealand’s valiant efforts, we are not going to do that.

We don’t have the political or social will to eliminate or eradicate covid.

But that means we HAVE TO continue to CONTROL covid!

That’s the only other option. THAT is what endemic means!
So, yes, our only viable choice left is covid becoming endemic. It didn’t have to be this way, but our leaders MADE a choice.

And now they need to make another choice: They need to choose an “acceptable” level of COVID death & disease.
Because pandemics don’t end by a disease just fading away, & pandemics don’t end with everyone able to completely forget about the disease.

Pandemics end when we decide how much death and disease we’re satisfied with.

I dont know about you, but for me—this👇🏼is too much death. Image
A good addendum here that, mathematically, “endemic” depends on Re & the relative changes in protected & susceptible populations.

Re isn’t completely up to us, but one goal of a control program is very often to get & keep it below 1.
Thread now available in French, thanks to the team at Atlantico 👇👇

And for those of you who like to read articles without seeing all the gifs, I have posted this thread to my Medium page.


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More from @EpiEllie

Jan 13

Honey is sweet and sticky and wonderful and everyone loves it, and babies are sweet and sticky and wonderful and everyone loves them.

But you should NEVER ever give honey to babies.


The short answer is: botulism.

The longer answer: a 🧵
What is botulism?

Botulism is the general name we give to several different diseases caused by the bacteria Clostridium botulinum.

This includes foodborne botulism, wound botulism, ‘iatrogenic’ (aka cosmetic) botulism and *infant* botulism.
Foodborne botulism, wound botulism, and iatrogenic botulism differ in what body part is affected but otherwise follow the same basic process.
Read 22 tweets
Jan 9
If everyone you know is suddenly getting “food poisoning”, just FYI that it is probably not actually food poisoning but is instead norovirus.

Norovirus (sometimes called “stomach flu” but not actually flu) is seasonal, and right now in the US it is norovirus season.
Norovirus symptoms are mostly vomiting, diarrhea, and cramps. But some people also have headache and fever.

Typically, symptoms last only a couple days, but for very young kids, very old people, or people who have weakened immune systems for any reason can be sick for longer.
Norovirus spreads by when uninfected people accidentally ingest the poop or vomit of an infected person (eww!).

This happens when teeny tiny bits of poop or vomit get onto other people, shared surfaces, or into shared food.
Read 13 tweets
Jan 6
I am a methodologist. Methods is a speciality. We make recipes for others to use.

When I publish methods, I include relevant code, equations, assumptions, & interpretations. I *intend* for people to re-use these.

Citation is expected. Quotation marks would be ridiculous.
For eg, if you are estimating a per-protocol effect of treatment adherence with treatment-confounder feedback using inverse probability weighting, I’ve shared my code & my papers with correct language for your methods & results sections.

Use it, cite it. Thats why it’s there.
Read 5 tweets
Dec 6, 2023
Me, an epidemiologist: research shows widespread mask use reduces respiratory infections

Me, an epidemiologist: research shows widespread mask use reduces respiratory infections

Them, another rando: oh yeah? Well one time I saw a mask and then I got sick, so how do you explain that, huh?!
Me, an epidemiologist: research shows widespread mask use reduces respiratory infections

Read 4 tweets
Dec 5, 2023
When people talk about masks & mask mandates for preventing respiratory infections, they love to talk about improper mask wearing.

And it’s true not everyone wears good masks correctly. But it’s also true that MOST people wear good masks well.

How many is most? About 85%.
Data from *Kentucky* show that during their mask mandates, 95% of people in indoor public spaces were seen to be wearing any mask.

And 87% of people were wearing masks that fully covered mouth and nose.

We did a separate study in Boston right around the same time — without knowing the Kentucky study was even happening.

What did we find?

95% of people were wearing masks in indoor public spaces. And 85% had them correctly over mouth & nose.
Read 9 tweets
Nov 13, 2023
Out now in Osteoarthritis and Cartilage: our new paper presents a graphical causal model for treatment of pain in knee osteoarthritis.

Open access link: oarsijournal.com/article/S1063-…
We outline a 6-step process for creating causal graphical models using scientific evidence and expert knowledge.

Identify core variables, create a list of potential covariates, conduct a semi-systematic literature review, discuss with experts, synthesize, and visualize. Image
What do we mean by "semi-systematic" literature review?

Like a systematic review, you begin with a carefully created search hedge: key words for your exposure, outcome, and/or other core variables, combined with your covariate list.
Read 22 tweets

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