Preferably, "How effective are masks against X under Y circumstance?"
In relation to Covid, I think it's likely masks reduced transmission. But, under normal social environments, did they reduce it by 5% or by 50%? It makes a big policy difference. It seems that studies are coalescing around masks having a 'real but small' effect, but I get it's a hard thing to study.
Separately, I was surprised to see that OP's article looked at studies starting in 1978, since modern electrostatic filtering masks were only patented in 1995--so I'm not sure how meaningful it is to lump studies on older mask technologies in with modern masks.
Either one would cause a dramatic reduction on the (exponential) virus spread.
For the actual policy, it shouldn't make a difference. It had feedback mechanisms anyway, because the conditions always change.
1) If the exponent is >1, it doesn't make much difference. Everyone will catch "it," for whatever disease.
2) It makes sense to have interventions prioritized by ROI
3) Many interventions are individual, and there is no exponent. Should I, as a [doctor / immuno-compromised-individual / patient / etc.] wear a mask?
The thing about masks is that the investment is minimal. Those 5% are still an incredibly large number that makes it a non-brainier.
If it decreases another order of magnitude, it may need some analysis. The OP has a point, but it's way beyond the plausibility window.
So in fact whether you wear one or not is far less relevant.
Not taking action to reduce risk of illness or death is irrational.
A quality mask costs around $1. Per-capita GDP is about $33 per day worldwide. Or put another way, with 8 billion people in the world, a mask a day runs around $3 trillion annually.
The world is interconnected.
I like masks since, aside from viruses, they filter pollution and allergens. I feel a lot better post-2020. However, universal HEPA filters and covid masks are very much for the rich.
I use each of my masks for probably at least 10 hours before throwing it away, and I've never gotten covid except once (in Jan or Feb 2020) before I started wearing masks (in fact, before anyone in my country -- the US -- knew about covid).
(I have to write "probably" because I don't actually keep written records of how long I have each mask on. I rarely have one on for more than an hour at a time.)
I've used mainly 3M 8511 masks.
The most important distinction between mask models is that some models have valves / vents and some do not.
Hospitals use ones without valves. The lack of a valve means that the part of the mask that filters the air gets a lot more damp than it would if a value were present (because exhaled air is damp) which might drastically reduce how long the mask will last, so that might be why some hospitals instruct their employees to use a new mask for each new patient contact.
The most important distinctions also include:
1) Fit. This matters a lot.
2) Nano versus electrostatic technology.
3) Filtration level. "N95" advertised isn't always 95% in reality, and some are 99+%.
4) Impedance to airflow
#4 is more than just comfort it determines how much air goes around the mask.
For some N95 masks, that's because they assume you are using it to block out particles that will accumulate on the mask, like paint droplets or sawdust or whatever.
In contrast, breath is mostly water vapor, and COVID-19 particles have a short-enough half-life that you can probably rotate between masks and be pretty safe.
More than once per day? It's complicated. There are two designs:
- Electrostatic masks work well so long as the mask remains charged (those are the 3M N95 ones). Efficiency drops as they become moist, especially. However, for good ones, even after extended use, it's still surprisingly high.
- Nano masks basically work forever. The initial efficiency is lower than electrostatic, but remains pretty good for longer than I'd want to use one.
For real-world use, I really prefer nano. Unless you're much more careful than I am, enough air leaks around the mask that I'm not sure there's a big difference between 99%, 95%, or even 80% filtration.
And the numbers are extremely conservative too -- they look at filtration around a few hundred nanometers, which is the worst-case. Most diseases come in on much larger droplets.
One thing which tends to be under-emphasized is that it's not binary. Viral load is important. A single virus particle probably won't cause an infection (it probably won't infect a cell, and if it does, your innate immune system will probably flush it). If it does cause an infection, your adaptive immune system has a lot of time to react, so it probably won't be a bad one.
This is even more true for pollution and allergens.
For my purposes, I find nano masks to be the right bang-for-the-buck. They're much more breathable too. And they handle environmentals like rain or sweat better.
The Asians are right; living in a big city, I've felt better since 2020, with masks, air quality monitors, and HEPA filters everywhere. I get sick less often, have milder seasonal allergies, and just generally do better.
On a related note, other aspects of air quality matter too: CO2 levels, humidity, etc.
Check your assumptions, please!
If you are comparing e^(kt) to e^(0.5 kt), sure, they’re very different. But Covid didn’t spread like that at all. It grew exponentially-ish until the fraction infected was no longer negligible, and then the dynamics changed dramatically, as they must have. After all, you can’t have 1 million times the entire population infected after a couple years.
Another issue is that most of these studies are just surveys. Did participants actually use their masks for x hours? Did they use their masks correctly?
And your belief is based on what?
Like it would be remarkable if it did nothing. THAT would be a blockbuster result.
The thing worth studying is if the effect is worth the trouble or not. It could be worth doing or it could effectively be a waste of time due to whatever other factor.
The other way round is far more difficult.
If you leak then you are wasting your time because in a static air environment you’ll delay the critical level build up by a few minutes at most.
Medicine doesn’t like aerosolisation because it sounds too much like miasmia theory.
So we have too much focus on droplets and fomites.
Fundamentally this should have been sorted with a properly designed trial with the correct protocol of sufficient size to answer the question. Given what was on the line why has it not been done?
That's an interesting question but if you're suggesting it implies something either direction: why?
Obviously there are a LOT of politicians and people strongly interested in a "masks are useless" position.
But it's not just that the "masks are useful" people have failed to satisfy you.
It's also that the "masks are not useful" crowd has not published a conclusive study of their own.
So it's not convincing to me that the truth is anything other than "masks have varying effectiveness, though the supply-chain-crunch plain-cloth-mask world of 2020 wasn't the ideal type of mask."
Do you have reason to believe an N95 isn't effective? What about a P99? (In the world of media I consume, these types of masks vs cloth masks are things that were widely discussed, along with PM2.5 etc. So the "it was presented as black and white" crowd seems just uniformed of their own volition, maybe watching too much partisan media who had an interest in presenting the issue in a one-sided manner.)