A long thread on #COVID19 prevention and face masks (which we should use) and sending the RIGHT message. Why? I worry about the unintended consequences of hardcore face mask advocacy, and don’t want this to end up with the public relations pitfalls of influenza vaccination...

...moderately useful but doesn’t make you bulletproof: oversimplified messaging can create elevated expectations. So, mask polarization has been fueled by explosion in mask “evidence” – models, lab droplet studies, rehashing the (poor) existing data- and weird politics...

So, droplet and filtration studies are interesting but experience IRL shows us transmission is complex: let’s see what data shows when people explictly are randomized to use masks and are followed for infection in a trial…(note only I trial involved cloth masks here.)

Most data is on influenza or general “influenza like illness” but the household attack rates are comparable to SARS-COV-2 (usually 10-20%) as is tranmission - this preprint review brings it together particularly nicely at https://www.qeios.com/read/1SC5L4  ... https://www.qeios.com/read/1SC5L4 

If you look at self reported infection outcomes, wider variation with a couple of big outlier studies: OR mask alone 0.9, 1.1, 0.39, .95, 1.16, 1.11, 0.32. OR of self reported infection with masks plus hand hygiene is more consistent - 0.78, 0.87, 0.77, 0.82, two "significant"

Of those, Barasheed is an outlier with larger protection-Hajj participants masked if they had symptoms or slept near symptomatic persons. Overall unimpressive - and self reported ILI is also a messy outcome honestly, is this similar to when your dentist asks you if you floss?

For lab confirmed influenza: looking at trials w/ masks and masks plus hand hygiene (HH) arms, HH is more compelling but face masks alone are really not – masks alone, odds ratio is no better to worse 0.97-2.51, but masks plus HH together look better, odds ratios: 0.77-0.82.

So actual RCT data, where people are GIVEN masks and followed, is pretty unimpressive. It’s mostly from university dorms and households - and my takeaway is masking PLUS HH seems to reduce risk by 20% or so maybe but masks alone – wide variation and hard to see effect.

Here’s the observational data – In self reported infection, face mask use odds ratios are all over the map: 0.85, 1.42, 0.48, 0.25, 1.57, 1.65, 0.79. For SARS 2004: 0.3-0.5. In lab confirmed flu, 0.51 for continuous use. These data are variable and frankly thin on the ground.

If we look for community based studies using the heterogenous intervention known as cloth masks (textiles vary in filtration efficiency from 3% to >60% and fit matters) we find…none. (sigh)

Nonetheless, modelling projections such as those from IHME are being put forth, and we see messaging like “Cases are rising, it is simple, wear a mask” This IHME model assumes 95% masking would avert deaths: looks like a no brainer!

The assumption is that masks can reduce respiratory infections by 33% but I genuinely don’t see how that is supported based on the data we just looked at/other data, and it seems both speculative and optimistic (as seen here - from IHME- unless I am seriously missing something.)

So: WHAT’S THE HARM? I mean, if masks just help a LITTLE, they likely help! (AKA, do we need an RCT to show that parachutes work?)
Well, the one RCT with a cloth mask arm (McIntyre, health care setting) had the highest infection rate in continuous cloth masking...not enough data

So - can cloth masks become a sodden virusfest on your face? The control arm was sometimes masking, so we can’t say either way. It is not excluded. Countries with extensive cloth mask history would somewhat suggest it is not WORSE however.

To me the REAL possible harm is detracting the concept of bundles or layers of prevention: just agitating about masks oversells an uncertain benefit. Hand hygiene and distancing are KEY and we need to talk about them IN THE SAME BREATH.

The other possible harm is DAMAGED TRUST-
trust is an earned commodity that saves lives and engages communities.
We need to share nuance and treat people as partners. Otherwise:
“I got the flu after a flu shot...“
OR
"I got COVID and I wear a mask

"...YOU LIED, IT DIDN'T WORK"

One more thing: WHO put together a bunch of info on “good” cloth masks – three layers, at least one spunbound (polypropylene), well fitted: specs of commercially available mask are lacking...we need that to happen. https://apps.who.int/iris/rest/bitstreams/1279750/retrieve

Public health officials are now in the weird position of being portrayed as blocking an intuitively obvious, “surefire” prevention technique for this devastating illness, and they’ve spent their whole professional lives studying optimal prevention. Strange times.

In summary:
Encourage people to: DISTANCE-HANDWASH-MASKS, and systems to: TEST-TRACE-ISOLATE
and,
Be clear and open about information changing -we can only do our best, with what we know now. Science is about adapting and learning.
(and if you’re "sure"-you may be wrong.)