In early March, our community in SF wasn't, on the whole, taking COVID-19 at all seriously. @math_rachel & I looked at the data, and we were worried it was about to blow up.

So we wrote an article saying so.
We didn't expect it our article make much of a difference, frankly. We're just data scientists, in our niche area of deep learning. Our most popular post, introducing @math_rachel's Natural Language Processing course, is our only post ever that has topped 100k unique readers
Much to our surprise, over half a million people read our article! Dozens of people emailed us to say that they used the article to convince their clubs, hospital clinics, workplaces, and so forth to shut down all non-urgent work and cancel gatherings
Anyway, that was that, and we moved on with our lives. We had a new deep learning course to teach. I needed a case study for how to interpret complex evidence, and on a whim, I picked masks.

I had no interest in masks, and assumed the evidence wouldn't show anything much.
In Feb, no-one was wearing masks in the West, except for a few Asian expat communities. We were told clearly that they didn't work and weren't recommended.
When I started studying the data on masks, I was absolutely stunned. It seemed that masks could be our best tool to slow the spread of COVID-19 - but no-one was talking about it!

…except for @zeynep, who wrote a brilliant piece in the @nytimes
So, I finished the lesson on masks, and taught my students. There were about 1000 people in my class (all remote of course), and they told me "MAKE THIS LESSON PUBLIC!"

So I popped it on YouTube, and thought that would be the end of that. It wasn't…
Imagine my surprise when a @washingtonpost editor contacted me, told me they'd seen the video, and wanted me to write an article about it for them! I said yes, of course - but had no idea how one goes about writing a good newspaper article.
I wrote a draft which summarized the video, and sent it to my @YGLvoices friends @wucker and @MarietjeSchaake, who are brilliant writers. I was amazed at how they turned my turgid prose into a crisp narrative.

The article turned out to be wildly popular!
This was the first time, AFAIK, that there was such a direct call in the mainstream English-language media for everyone to where DIY masks.

Astonishingly, TV shows started calling me! Comms expert @bhalle87 kindly agreed to help get me booked, and the next day I was on @GMA!
The @GMA story was hugely important, because not only did they discuss my article and interview me, but they also interviewed Fauci. This turned out to be the first time he said on the record that masks can help when used by the public.
One of the really amazing things after my article came out is that scientists started writing to me and sending me their unpublished research about masks. It turns out that many people weren't able to discuss community mask use at that time, because it was against CDC guidelines
So I found myself as something of a "go-between", helping communicate the scientific research, in an environment where academics weren't easily able to do so themselves.

The comments from Fauci made it less taboo for scientists to talk about public mask use.
Frankly, until this point, most of my approach was to simply plagiarize what @PetrLudwig had already done in Czechia. You see, I knew that Petr's approach worked, because he got his whole country wearing masks in three days, as @TheEconomist explained.
This is the brilliant video from @PetrLudwig which set the basic strategy that we've been using ever since (he also did one in his native Czech language).
To be clear, this was an extremely weird and uncomfortable position for me. I've never been involved in politics or been an advocate. But in our courses we push our students to use data for good - not just analysis, but follow it all the way through.

So I had to walk the walk!
I realized that the biggest thing stopping progress on community mask use in the use was the @CDCgov wasn't recommending them. So I focused on that, and tried to ratchet up the public pressure.
I was lucky enough to know folks that had first hand knowledge of what was happening in the CDC, and was told there was a concern that the science wasn't strong enough.

So I reached out to some of the world's top scientists & asked for help reviewing the evidence. They said yes!
Generally, most scientific papers get viewed a few dozen times. Many don't get read at all. So what happened next was a big surprise to us all - it rapidly became the most widely viewed paper of all time on !
It also generated many comments thru  open review. Many of them were thoughtful and interesting points which, frankly, we hadn't considered fully. @reshamas categorized every comment, and we made sure we handled every one in our revised draft.
I made sure that folks at the CDC saw our paper, and, although it's impossible to know for sure, I hope that it might have been helpful in getting them to finally shift their guidance! (I've heard from some folks with internal knowledge that it was a factor in their decision.)
As well as working hard on the research, there was also a lot of media requests to handle. Many of them were from small local radio and TV stations, but I tried to say yes to every request.

Appearing on MSNBC with @ashishkjha was a great opportunity.
I was lucky enough to get to know some of these amazing folks, like @HeleneMarivdW and Arne von Delft, who also were co-authors on our paper. Their experience with TB had an amazing amount of overlap with what we were seeing with COVID-19, so they had great advice for us.
(I will finished this tweet thread later today.)
I pointed out to Trish that source control was particularly important, and it wasn't discussed in her paper.

I was so happy when she agreed to co-author an article about the science of masks with me!
One of the wonderful things about this whole campaign for me has been that far more accomplished and credentialed people (like @trishgreenhalgh!) have been willing to put in a lot of time and effort working with me, even although I'm just a data scientist.
Trish and I started getting lots of requests to appear on UK TV and radio. Finally, in the UK the possibility that masks might be useful in public was starting to get attention!
Meanwhile, in the US, it was clear that @CDCgov just "recommending" masks wasn't enough. People still weren't wearing them. I DM'd @VincentRK, who was kind enough to agree to a call about the issue. We decided to try and write a letter and get lots of scientists to sign it.
I wrote the first draft of the letter, and Vincent got to work finding signatories. He knows just about everyone, so he quickly had sent a request off to nearly a hundred medical experts to sign our letter. About 95% of the recipients said YES right away!
I can't begin to describe what a privilege it has been to work with @zeynep throughout this campaign. She's an amazing writer and thinker. I was so privileged that she and @trishgreenhalgh agreed to co-author an article about source control with me.
Honestly, working with people like this has been constant imposter syndrome for me.

I always feel very awkward composing an email or making a call. I never quite understand why these incredibly impressive people reply. But I'm glad they do.
Sometimes, it's hard to know whether we're really making a difference. But sometimes we see that we are, such as when the President of the Czech Republic said he sent my article to other world leaders!
In the US, it started becoming clear that masks were becoming a partisan issue. @DavidLKeating did an amazing job of looking for top PR firms with strong connections to conservative media, and PlusPR were kind enough to agree to work pro-bono for us. 
. @plus_comms helped me to get interviews on right-leaning networks like @newsmax. I really enjoyed my chat on American Agenda and thought the hosts asked terrific questions. I had nothing but good experiences on conservative media TV and radio.
Oh BTW, here's something I haven't shared before… A few months ago I tried to find everyone I knew that knows a US governor, and made a video which I asked them all to share with the governor.

Here's that video.
I made quite a few little hands-on videos. I'm not a arty/crafty person so it was a bit out of my comfort zone.

But there was so little real info on masks, so I tried my best. Here's my first - showing how to make a cloth mask.
I started seeing claims that cloth masks couldn't actually block droplets, so I created something showing they can.
And then I started seeing claims that masks lead to oxygen deprivation, so I made a video showing that's not actually what happens at all.
Although I've done a lot of media appearances, my favorites have always been talking to @abc7kristensze. And my favorite chat with her is this one, where we actually "stepped up our face coverings" live on air!
Kristin always does such careful research, including, in this case, going over the steps with me a number of times before the show to ensure she had everything working perfectly.

The show even keeps going on Facebook during ad breaks, so she's working constantly for hours!
One of the challenges of an advocacy campaign like this is that there are SO MANY people to reach! Lots of different geographies, and lots of different markets. CNN Business reaches a *lot* of people, so that was a great place to go.
We saw the same thing in the UK - no mask requirements until the death count was through the roof, despite the great work of @SadiqKhan and his team. (And I know from personal experience that Sadiq has been directly involved in this, and that he cares deeply about it).
It's not just that governments and health bodies ignore masks. It's that they nearly always make public statements about how useless they are. Or patronize us, "it's sweet that people think they're helping".

Then they bring in mask laws, & wonder why people don't listen!
Unfortunately, we've seen in every jurisdiction where governments initially resisted masks, that just recommending masks doesn't work. Most people don't wear them until there's a mandate.
One of the hardest questions I get is "what is Masks4All, exactly". It's rather hard to say! Originally, it was a hashtag that @PetrLudwig came up with, which he expanded into a national campaign in the Czech Republic. We worked together, along with many others, to make it global
Most of the people involved in Masks4All campaigns around the world are scientists and doctors. They're all working as volunteers. Personally, I've working on this well over 40 hours a week for the last four months, whilst also handling my day job and helping look after a 4yo.
I've noticed that these scientists and doctors working as volunteers almost never get any thanks from the policy makers who ignore them for months, and then finally change their policy, without credit or apology.

I've also noticed they never ask for credit or apology.
So, why am I retiring now?

It's NOT because the work is finished. People need to keep wearing masks until at least after winter, wherever there's community transmission. And probably until there's a vaccine.
It's because now that public health bodies are finally onboard in nearly every country, there are now people being paid to work on this. There's funding for research, funding for marketing, and funding for policy development.

It's time to stop expecting volunteers to do it all.
I still have a few incomplete projects, which I'll see to the end. But I'm not going to take on any new projects, and I'll limit media to only the occasional appearance on national channels.

(and @abc7kristensze, of course!)
This whole thread is focused on my little part of the story. So many other people were involved in many ways.

In particular, many aerosol scientists were critical in running a critical parallel campaign, including @kprather88, @linseymarr, @Don_Milton, @lidiamorawska, and more.
You can follow @jeremyphoward.
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