The CDC recommends wearing masks outdoors. You may wonder, how effective are masks? What’s the difference between wearing a N95 mask vs a cloth one? We will explore answers to these questions and more.
Let’s run some SEIR simulations built off of our Shopping Solo simulations. People marked with a black border are wearing a cloth mask at all times: those wearing masks emit 80% fewer viral particles vs those who don’t, but inhale the same amount. This mask behavior is based on CDC guidance, and all parameters are at this footnote1.
You can configure the percentage of people who wear masks and see the impact on disease spread.
Note how infected people with a mask have a smaller cloud of particles around them, vs those without a mask.
Running this simulation 10,000x, there is a clear relationship between mask wearing and infection rates: mask wearing reduces infection rates.
Looking more closely at the data, there is an interesting second-order effect: a backwards “S-curve”.
When about half of people are wearing masks, each additional mask wearer can prevent the most number of infections.
Intuitively, this makes sense:
Unlike ordinary masks, N95 masks reduce inhaled particles by 95%3, theoretically reducing the wearer’s infection risk. They are uncomfortable to wear, currently in short supply, and the CDC recommends saving them for healthcare workers. But in simulation they are neither in short supply nor uncomfortable, so we can ask
How do N95 masks compare against regular masks?
People marked with a thick black border are wearing a N95 mask; no border, no mask. People with N95 masks inhale fewer viral particles than those who don’t, and all parameters are at this footnote4.
It is no surprise that N95 masks are more effective than cloth masks, but just how much more effective are they?
Both types of masks can control the spread with a critical mass of wearers. The critical mass for N95 masks is lower than that for regular masks, but not as large as you might imagine. For a max tolerable infection rate, we only need 10-15% more adoption of regular masks vs N95 masks to stay under that limit.
|To keep infection rate under:||% of cloth mask wearers required||% of N95 mask wearers required|
For each max tolerable infection rate, we only need modestly more adoption of cloth masks vs N95 masks to stay under that rate.
Given the shortage of N95 masks, aiming for a modestly higher rate of regular mask usage is more practical policy.
A cloth mask does not offer direct protection against inhaling viral particles5; for a N95 mask, it depends.
When there is a low percentage of people wearing masks, wearing a N95 mask can significantly decrease your infection risk6. This advantage fades as more people wear masks and the riskiness of the environment falls, which underscores a key takeaway from our Shopping Solo simulations.
Our decisions matter more when our community is more at risk.
The best way to combat this virus is to make data-driven policies and decisions. High quality simulations offer a fast and safe way to estimate the risk of our actions.
That being said, the virus modeled above is not Covid-19 the dots are not shopping the same way we shop: we touch shopping carts, swipe credit cards, maintain distance in stores, and so on. Researchers are discovering more about Covid-19 every day, about how it spreads, symptoms it produces, how to treat it, and so on.
Future work will focus on incorporating the latest research and simulating more realistic human
behavior. These simulations are all open source.
You can reach out to me privately at
email@example.com or on Twitter.
Please share these simulations if you found them informative - as the above data shows, we all need to work together to control the spread of the virus.
I built some #Coronavirus simulations, exploring the impact of wearing cloth vs N95 masks. We should all wear masks outdoors, but there is an inflection point where mask wearing is super effective.https://t.co/AgfV48ghVV pic.twitter.com/cpbYBUikHJ— Jin Pan (@JinPan20) May 22, 2020
Cloth Mask Simulation parameters:
If your community has a high rate of mask wearers, you should still wear masks! The more people we see wearing masks, the more normal we will consider masks to be, and the more we will wear them. ↩
N95 Mask Simulation Parameters:
One of the primary transmission vectors of the virus is from touching some viral particles, and then touching your face. Mask wearing can reduce the amount of face touching, which provides some protection against the virus, but that is not captured in this simulation. ↩
I debated internally about whether it is ethical to publish this, since there is a real shortage of N95 masks. In the end, I’m publishing these findings because the advantage of N95 masks is strongest when only few people are wearing masks at all. If acted on, this published finding would only impact a few masks. Plus, I see people at my local Costco (which has 80+% mask usage) with N95 masks, so this may convince them that they’re not that necessary. And orthogonally, not publishing this would be lying by omission. ↩