This study about the effectiveness of mask wearing doesn’t say or imply what a lot of people seem to think it is concluding.

First, there are two aspects of mask wearing that people seem to conflate (which if you read this study carefully, the authors do not):

1) Source control.

2) Protective effect.

This study examines the latter and while it seems mostly solid, it has severe limitations, too. I’ll cover those in a bit. But first, “source control” means preventing you from infecting others, while the “protective effect” means your mask protecting you from infection.

It’s already well-established, as the study itself acknowledges, that source control is an effective use of masks.

Observational evidence supports the efficacy of face masks in health care settings and as source control in patients infected with SARS-CoV-2 or other coronaviruses.

Note again that this study is about number 2, “protective effect,” and not about source control, which already is known to work. See here and here for more information about how well-supported this is.

Again, for the hard of reading, the study I linked to at the top of my post was only examining the protective effect of mask wearing, not source control. We already know source control works. It’s less well-established how much of a protective effect there is. From the studies I’ve read (and I’ve read nearly all the literature that currently exists in the world for this), I believe there is a protective effect, and furthermore that even if you are infected, wearing a mark reduces the viral load and causes the infection to be less severe.

The limitations of the study, as I mentioned I’d discuss, is that it doesn’t seem to control for home infection (most likely source of all infections) and the positivity rate was not high enough for this study to be statistically significant. These are quite large limitations, as the authors themselves mostly acknowledge.

All that said, remember that in many people Covid-19 is asymptomatic or barely symptomatic, and that unlike other similar viruses an infected person can transmit it during the incubation period.

So, if you don’t care about infecting others don’t wear a mask. Freedom! But if you do care about source control, wear your mask when you’re indoors in public. It’s the sane and rational thing to do, and every bit of evidence we have supports that source control works, even with cloth masks.