[katieHaylor (OP)]

Monika says:

There are various graphics floating around on social media showing how mask wearing reduces the chances of catching Covid. They usually show, in a row, an infected person not wearing a mask, a healthy person wearing one, the infected person wearing one and both of them wearing one, and gives a percentage for the chance of transmitting the virus in each case. Often, the last one is both of them wearing the mask, and staying 2m apart.

All these graphics are missing the one where the two people are NOT wearing a mask, and staying 2m apart, for comparison's sake.

What is the percentage of transmission when an infected person and a healthy person are 2m apart? Does wearing a mask at that distance even make a difference? Here in Canada, the government guideline is to stay 2m apart, and wear a mask where that distance can't be kept (such as in a store). In many places, masks are mandatory regardless of how close people are to each other. Which makes more sense?

[alancalverd]

Once you are wearing a mask, you are wearing it regardless of the subsequent behavior of others.

You can't rely on the kindness of strangers to protect you, and there are plenty of infectious idiots about who don't know or don't care what 2m looks like. Including the President of the United States and his Senate majority, and the unelected President Cummings of the UK.

[evan_au]

Does wearing a mask make a difference if you're standing 2 metres away?

Yes. Every little bit helps.

Some Assumptions
Let's say a typical mask worn by a typical untrained person reduces your chance of infection by 50% (ie it halves the number of virus particles you are likely to breathe in).

I have heard suggestions that staying 1m away from an infected person reduces the chance of infection by 80% (a factor of 5).
- Stories are more varied when you increase to 2m - but let's say it reduces by another factor of 5.

Calculations:
- 1m separation, no mask: 5x reduction
- 1m separation, with mask: 10x reduction
- 2m separation, no mask: 25x reduction
- 2m separation, with mask: 50x reduction

Feel free to plug in your own numbers: If you have a high-quality mask, and know how to fit it properly, then plug in 4x reduction in chance of infection for the mask.

PS: Of course, an infected person in an outdoor area will leave a lower density of viral particles than the same person in an indoor area with all the windows closed...
- I haven't seen comparisons for indoors vs outdoors, but this may have a larger effect than wearing a mask.
- But every little bit helps....