I think face masks are pretty cool. They’re the hot fashion trend of 2020 and they save lungs and lives. They’ve become a hot topic of political positioning as well, which goes to show how little thought many people give to what they do. Lungs don’t subscribe to any political ideology and they aren’t card-carrying members of a political party. Neither is CoV-2. CoV-2 loves all humans regardless of where they live on the political spectrum.
What I am going to propose here, is that you take a Bayesian point of view in determining your position on whether or not you should wear a mask. By Bayesian, I mean a philosophy of science or model of reasoning. Being Bayesian in this sense, vs. the actual statistical analysis sense, means looking at the evidence and changing your viewpoint by valuing multiple lines of evidence appropriately. So we’re going to look at the available evidence, and make decisions based on what’s most likely to be in line with that evidence. I hope you can see this will likely produce a better conclusion than whether you like Trump or not.
First up, I will look at a meta-analysis. Meta’s are cool because they are a review of lots of studies which give them quite a bit of predictive power. This meta looked at 172 studies in 16 countries (that’s a lot of data) and they found that a distance of 1 meter (a little over 3 feet) reduced infection transmission vs. distances closer than 1 meter. Protection increased as distance increased. This is what people mean when they talk about social distancing, which I prefer to call physical distancing. Be as social as you like, at a distance. Face mask use could result in a large reduction in risk of infection, especially with the N95 respirator masks.¹
The next study we’ll peek at was conducted with 246 people sick with acute respiratory illness. They had 50% of the people exhale without a mask, and 50% with a mask. They collected their breath samples. They detected coronavirus droplets and aerosols in 30% and 40% respectively of the people without masks, and 0% in the masked people.²
Next up is a study specifically testing if face mask use can help reduce transmission within a household where someone was sick with COVID-19. What’s instructive of this particular study is that wearing a face mask before symptoms were identified reduced transmission by 79%. Once the person was sick, the mask was not particularly effective at reducing transmission. What do you make of this? That the most infectious time of an infected CoV-2 person is before they know they’re sick!³
This next piece of the evidence puzzle is actually a model vs. a study. Using mathematical modeling techniques in two different models, it was found that “when face masks are used by the public all the time (not just from when symptoms first appear), the effective reproduction number, Re, can be decreased below 1, leading to the mitigation of epidemic spread. Under certain conditions, when lock-down periods are implemented in combination with 100% face mask use, there is vastly less disease spread, secondary and tertiary waves are flattened and the epidemic is brought under control. The effect occurs even when it is assumed that face masks are only 50% effective at capturing exhaled virus inoculum with an equal or lower efficiency on inhalation.”¼
This fascinating study showed that by putting a nylon stocking over any cloth mask, it can be improved to be even more effective at filtration than a tight fitting N95 respirator mask. ½
Okay, so now let’s come to some conclusions and decide the best course of action to take to protect ourselves, and those around us (even if you don’t care about anyone else). Let’s consider what we know fairly well:
- Coronaviruses exist. They cause colds and other respiratory illnesses.
- CoV-2 exists. It is a new, or novel coronavirus for which we have no natural immunity. It causes COVID-19.
- COVID-19 is a new disease which we know little about. It effects people differently; from asymptomatic to deadly.
- CoV-2 is transmitted from person to person through respiratory droplets and aerosols exhaled while talking, shouting, laughing, coughing and even just normal breathing.
- CoV-2 appears most infectious in the early stages of infection, before the person is aware they have been infected.
There’s lots of other things we can consider, but armed with this knowledge we can look at the evidence and make some practical decisions. We should maintain a distance from each other of at least 1 meter, or 3 feet, with more distance being more protective. We should wear some type of face covering, the closer fitting around the nose and mouth the better. We should wear it whenever we are going to encounter other people.
These basic conclusions are hard to argue with based on what we know about the current pandemic caused by CoV-2 and the evidence we have around mitigation of spreading the disease. COVID-19 is raging in many countries around the world, the United States being one of them. In certain states the rate of infection transmission is increasing exponentially making encountering other people in our day to day lives ever more problematic. The best course of action remains to:
- Stay home when you can.
- Avoid large groups of people, especially indoors.
- Keep your distance from others, even one on one.
- Wear a mask covering your nose and mouth when out and about where encountering other people is likely.
This should seem obvious at this point, but unfortunately, it is not due to ignorance, stubbornness, misinformation and disinformation, and a pervasive recklessness that infects the human brain apparently as effectively as CoV-2 infects the human respiratory tract.
² Respiratory viral shedding in exhaled breath and efficacy of face masks
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