Changing the CDC mask infographic narrative from “I” to “we”
I’ve been wanting to share that CDC infographic about the benefits of wearing a mask, but it bothers me that it boils pandemic response down to “you do you” when we know that a collective response is far more effective and, frankly, necessary.
So I made my own to show the difference between “I” and “we” when it comes to the pandemic.
Why are the numbers in the CDC infographic different?
The CDC infographic is based on a self report survey. The study did not account for other behaviours that may have altered someone’s risk. For example, it’s likely that someone who wears an N95 mask in all indoor public settings also takes other precautions that reduce their risk of COVID and so the 83% result in the infographic would be the result of all their behaviours, not just mask wearing.
I used data from microcovid.org, a site that helps people to compare the relative risk of different scenarios based on, among other things, the masks worn. The data in microcovid.org is based on studies of the effectiveness of masks in filtering the air and so allows you to isolate the expected impact of wearing different types of masks from other behaviour.
To generate the numbers for the infographic, I started with a base scenario of spending 2 hours with someone who has COVID. I chose this scenario because it eliminates variability based on the location. Microcovid.org pulls in data of cases in different countries and uses that to estimate how likely the people around you in a scenario are to have COVID. This data changes between different parts of the world and changes week to week as infection rates are updated, so using a scenario that assumes someone has COVID eliminates this variability and makes it easier to replicate and check the results.
From this starting point, I generated multiple scenarios by changing the settings for “your mask” and “their mask” and took note of the estimated “microcovids” — a unit made up by the authors of the site to compare the risk of getting COVID across different scenarios.
A couple of assumptions:
For cloth masks I assume “thick and snug”. A lower quality mask seems a less likely choice for someone who is still wearing a mask at this point in the pandemic.
However, for the “their mask”, everyone wearing snug, thick cloth masks seems unlikely, so I’ve chosen the lesser of the two options.
For N95s I always assume it is not sealed or fit tested, even for people who choose N95s. Information on fit testing is not widely available, and so it’s less likely they’d have done that, so it seemed a more realistic choice.
You can see though in the figures to the right I’ve added a scenario that shows the advantage this gives an individual if they are able to seal the mask which I left out of the infographic for simplicity.
Here’s a video of how to do a fit test yourself to improve the seal of your N95 mask.
Taking these figures, I then calculated the risk reduction relative to the scenario where no-one wears masks.
The green and blue cells are the final results that went into the infographic.
The results speak for themselves. Imagine if we were able to consistently reduce the spread of not just COVID, but all airborne contagious disease, by 94%. How much healthier would we all be?
One advantage of N95s that these results don’t capture is how much harder it is to wear the mask badly. No doubt some people will still find a way, but an N95 won’t fall below the nose, and isn’t comfortable to pull down to only cover the mouth.
Here’s the spreadsheet with all the calculations.
Stay safe and take care of one another!
