Much of the confusion about masks is because people conflate preventing infection (PPE for hospitals) with stopping transmission (cloth masks for all). Share this explainer I wrote with @jeremyphoward &
@trishgreenhalgh with your mask-skeptical friends! https://www.theatlantic.com/health/archive/2020/04/dont-wear-mask-yourself/610336/

Once we understand this distinction, that the point of masks for all isn't to act the way PPE does for hospital workers, much of the confusion disappears! Advice that applies to PPE (strict donning/doffing) don't really apply to masks for "source control"—stopping transmission.

PPE for medical workers is *individual* protection. Masks for all is something different: it's a *public good*. It works only if almost everyone complies and once that happens it's a really powerful benefit for everyone. It's like clean air: need filters on all chimneys/exhausts.

A public good like masks for all cannot be measured as an individual benefit. So we did some population level-modeling. If we can get 80+% of people to wear masks, we could help push R below 1. All models have limits (next tweet) but it's a strong argument! (Blue is R below 1).

A few limits: Not all transmission happens where cloth masks would help. For example: household transmission, healthcare settings where transmission occurs despite PPE because medical workers do high-risk procedures AND masks don't replace the value of distancing! They add to it.

Reading so many articles which cited studies about protecting medical folks from infection to argue "masks are complicated" has been super frustrating. PPE *is* difficult to do correctly. Cloth masks for all to prevent transmission is different! THE DIFFERENCE IS NOT COMPLICATED.

Folks, for clarity: As I stated in everything I have written to date, all this is a proposal to wear masks *in addition to* social distancing and hygiene measures. ( @yaneerbaryam thinks people might misunderstand and I want to make sure!). MASKS ARE AN ADDITIONAL MEASURE.