Thread by @AkivaMCohen

OK. Time for a thread on masks. Anti-maskers (who should be as reviled as anti-vaxxers) keep citing research studies showing masks aren't that effective at protecting wearers from becoming infected. You need to know why the anti-maskers are wrong. It's a basic mistake

The anti-maskers are (sometimes deliberately, sometimes ignorantly) confusing SOURCE CONTROL with INFECTION CONTROL.

What does that mean?

"Infection control" means "protecting the wearer from being infected". When a hospital worker puts on PPE and a properly fitted N95 mask to go take care of a patient on airborne precautions - someone sick with an airborne respiratory virus - they're engaging in infection control.

The reason they are putting the PPE and mask on is to protect THEMSELVES from being infected by the patient. That's why it's important to have a properly fitted n95 mask: one that seals to the wearer's face, without gaps that virus particles in the air can flow through.

Cloth face masks, surgical masks, improperly fitted n95 masks - none of those do a very good job of infection control, because virus in the air can get to the wearer through the openings. There are studies showing that, which the anti-maskers point to.

But "source control" is different. Source control means controlling the *source* of the virus by having *the infected person* wear a mask to limit the amount of virus they put out into the air by breathing, talking, coughing, etc.

With source control, proper fit, etc., isn't as important. Why? Because we aren't talking about preventing free-floating virus from finding a path to someone else. We are talking about preventing the virus from becoming free floating to begin with.

How does the virus get out into the air? From your nose and mouth, as you breathe and cough and talk, etc. And where is the mask? Directly in front of your nose and mouth. So it scoops up or deflects virus particles as they are expelled, minimizing what gets out to infect others

And do scientific studies back that up? Yes. They do. Here are some.

A 2016 study on the effectiveness of masks as source control studied two types of surgical masks and sealed and unsealed n95s. It found that ALL mask types used as source control "markedly reduced" the exposure for other people

ncbi.nlm.nih.gov/pmc/articles/P…

And "During coughing, source control was clearly superior to masking the Receiver" (i.e. infection control).

This is another 2016 article. The study was too small to reach statistically significant conclusions, but also found that mask use as source control had an impact (basically, "looks like it, but we need a larger study to confirm") pubmed.ncbi.nlm.nih.gov/28039289/

Here's a literature review, in the COVID context, that the authors summed up as follows: "Cloth masks are a simple, economic and sustainable alternative to surgical masks as a means of source control of SARS-CoV-2 in the general community"

ncbi.nlm.nih.gov/pmc/articles/P…

Here's one of the underlying studies they cited, which shows that surgical masks successfully prevented wearers from putting out viral particles

nature.com/articles/s4159…

Here's a 2013 study that showed that use of masks for source control actually provided the other person better protection from infection than having that person wear an n95 mask for infection control

liebertpub.com/doi/10.1089/ja…

So everyone should be clear on this. The science strongly supports the conclusion that widespread mask use as source control would meaningfully decrease the chances of people getting infected.

But wait, that's only for infected people! I'm not infected, why do *I* need to wear a mask?

Because with this virus, you can be infected but not know it (because symptoms don't start right away) and infect others at that time. So mask on, just in case.

Last thing. You know who else knows that source control works?

Your mother. And your kindergarten teachers.

Why do you think they taught you to cover your mouth when you cough??