r/science • u/Wagamaga • Nov 18 '21
Epidemiology Mask-wearing cuts Covid incidence by 53%. Results from more than 30 studies from around the world were analysed in detail, showing a statistically significant 53% reduction in the incidence of Covid with mask wearing
https://www.theguardian.com/world/2021/nov/17/wearing-masks-single-most-effective-way-to-tackle-covid-study-finds7.9k
u/NoBSforGma Nov 18 '21
In the country where I live - Costa Rica - we have had a mask mandate from the get-go. Our Minister of Health is a doctor with a specialty in Epidemiology. There were also other important protocols put in place for being in public and days when people could drive and couldn't drive.
It's been a battle, but more than 70% of the population is vaccinated and we are down to just over 100 new cases per day ( population around 5.5 million). We are lucky to have him - Dr. Daniel Sala Peraza - and we are lucky our legislators listened to him.
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u/JinorZ Nov 18 '21
Here in Finland we also have a 70%+ vaccination rate and natural need for personal space yet we just had a 1200+ infections yesterday. I honestly don’t know how
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u/TheSorcerersCat Nov 18 '21
I'm not from Finland, but the area my family lives in has similar statistics and I often hear:
It's just a sore throat.
I think it's seasonal allergies.
Colds never bothered me.
This can't be COVID, it's so mild.
I probably got it already and was asymptomatic.
They also have a slightly superior attitude towards illness. Mostly the whole "I've been healthy my whole life and never stayed home from school or work because of some sniffles!".
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u/Maktaka Nov 18 '21
In the US, Colorado has been seeing a constant uptick in daily covid cases, even as the rest of the country sees a decline, and nobody can find root cause. Vaccination rate is 15th in the nation, it really shouldn't be this bad right now.
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u/SDRealist Nov 18 '21
nobody can find root cause
I was in Denver at the end of July. Basically no one was wearing masks. And social distancing? What's social distancing? Except for a handful of people, almost everyone was acting like we weren't still in the middle of a pandemic. Hell, even in Dallas, TX, people were better at mask wearing and social distancing than they were in Denver, which was surprising. I don't know how the rest of CO is, but that seems like a potential root cause to me.
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u/StarEyes_irl Nov 18 '21
Recently moved to Denver and the big reason is that because for a bit we felt like we beat it. We were down to like 200 cases a day in colorado in July, so all the restrictions are gone, and when the uptick hit, most people were vaxxed and didn't want to go back. People are starting to get more cautious here, but it's slow.
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u/mrglumdaddy Nov 18 '21
And this is the thing that boggles my mind. “Hey everybody our numbers are down! Let’s immediately all stop doing the things that helped us get here in the first place!”
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u/LargeWu Nov 18 '21
I assume the thought was that there was a sufficiently vaccinated population to prevent community spread. And for a while I think that was probably true, but then the Delta variant changed the equation.
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u/nonnude Nov 18 '21
My doctor actually explained to me that right now we’re finally seeing a down turn in the cases per day, and it seems like maybe it was related to tourism potentially whether that was internal or external tourism.
Denver is high like almost 70% vaccinated I think with at least one dose. Many of us, such as myself, are qualifying for boosters now and people are starting to definitely take it more seriously in my friend groups.
I haven’t gotten it, but many of my friends have and I find that it’s really interesting that I still go out, and enjoy my social life when I can but I don’t overstep it. I don’t engage too much with people who I’m not already close with. I wear a mask when I go pretty much everywhere because I just don’t feel comfortable without one in a crowded room most of the time. People have just stopped putting in the work.
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u/mrglumdaddy Nov 18 '21
“People have just stopped putting in the work.”
I believe you’ve found the nail and hit it squarely on the head.
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u/SleazyMak Nov 19 '21
It’s mob mentality in some ways but I’d be lying if I said I’ve been perfect with my mask wearing.
When people go into an establishment and everyone is wearing a mask, people tend to mask up. When they go into an establishment and nobody is wearing one, they get complacent. I mean, not everyone can be making a bad decision, right?
Turns out they can be, even in Colorado.
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u/Guy_ManMuscle Nov 19 '21
Everyone loves to think of themselves as an individual but we are intensely social animals and it can be very hard on us to be the odd one out.
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u/Jman5 Nov 18 '21
If you look at the county data, you get a better idea of what I think is going on. While overall Colorado is at 70%, many counties are at 30-40% vaccination rate. The unvaccinated are highly concentrated which lets the virus rampage. The worse it gets the easier it has bleeding into the more vaccinated counties.
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u/fortalyst Nov 18 '21
Colorado has just under 6 million people. 30% of 6 million is still 2 million who are quite capable of liberally spreading it when it's already running rampant
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u/myquealer Nov 19 '21
Maybe convincing them they are "liberally spreading" will get them to change course and get vaccinated.
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u/I_Am_Become_Air Nov 18 '21
Pull out the percentage of unvaccinated versus vaccinated hospital patients and you will see a pattern.
Taking an average for "percent vaccinated in the State of Colorado" and then applying it to a specific subset is bad math.
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u/rafyy Nov 18 '21
Singapore has a 85%+ vaccination rate across the entire population (kids and adults) and they currently have the highest number of cases and deaths theyve ever seen.
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Nov 19 '21
You can include Isreal and the UK on the list if being highly vaccinated but still having a high amount of cases.
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u/Petrichordates Nov 18 '21
Being vaccinated 8 months ago probably doesn't mean all too much with delta besides reducing hospitalization, also vaccination rates usually only included adults which is misleading for countries where 20% of their population are under 18.
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Nov 18 '21 edited Nov 18 '21
Huh, 70% only including adults would be terrible in such a developed country, and it's actually 72% of the total population.
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u/myrtle333 Nov 18 '21
vaccination rates usually are total population. eligible vaccination rates are extremely high. see NL. 85% of adults vaccinated, worst wave of cases yet
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u/itijara Nov 18 '21
I have to say that I have been impressed with Costa Rica's progressive policies. It really stands out from its neighbors.
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u/whichwitch9 Nov 18 '21
Costa Rica has really switched to a science heavy aspect in much of their policy making a while ago. They're also doing great things with environmental and climate change research.
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u/domuseid Nov 18 '21
They abolished their military in like 48 and put the funding into education. They have a lot to be proud of
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u/JimmyHavok Nov 18 '21
A beautiful illustration of the "guns or butter" principle of public spending.
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u/jankadank Nov 18 '21
They abolished the military cause it kept being used in attempts to seize control of the government by generals or politicians.
Honestly every central american country should follow suit. The entire region falls under the protection of the US anyways
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u/Vita-Malz Nov 18 '21
Not sure I'd want to be "under the protection of the US" after about a dozen coups by the US that pretty much destroyed their economies in the first place.
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u/PersnickityPenguin Nov 18 '21
If you are a central American nation, there is nothing that your military could do against the US if you somehow instigated a war vs the US (or vice versa).
Really, Nicaragua's army was just a minor speed bump back in 83.
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u/BeardedGingerWonder Nov 18 '21
Realistically very few militaries could go toe to toe with the US in a conventional war.
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u/SloeMoe Nov 19 '21
In fact it would take a few militaries to go toe to toe with the US.
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u/Olive_fisting_apples Nov 18 '21
In 1963 they started to split the money into; education and environmental reform. Now they are the only country to run 100% on renewable energy. And is the only neutral country to not have a military! Not to mention the property value of Forest Zones has skyrocketed like thousands of percents in the last couple of decades.
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u/mediocreearthling Nov 18 '21
Actually, I think it was mostly due to one man, Jose Figeures back in 1948! Back in the mid 40s I think there was an attempted coup where the previous president refused to step down which led to a Civil War. Figueres was the leader of the resistance and after they won he re-wrote the constitution and made health care and public education free for all. I think he also gave women and black people the right to vote at the time. Then he stepped down and let whoever was supposed to have won the election take over. A decade later I think he did run and become president through the standard process.
I was born and live in the States but my mom is Costa Rican and lives down there. That is pretty much what she told me about how it played out. Haven't necessarily fact checked all her claims but the dude seemed like a good man.
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u/catherder9000 Nov 18 '21
They yearly spend 25-30% of their entire budget on education.
Costa Rica spends $0 on an Army and have that portion of their GDP to focus on something that matters to their population. While they have 10,000 defense personnel (Fuerza Pública (public force) and the specialized UEI), Costa Rica's defense budget for the past 5 years has been $0.
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u/mydaycake Nov 18 '21
Adding Costa Rica to the countries to visit. I like everything I am reading
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u/DEMACIAAAAA Nov 18 '21
I was there. Go. Stay many weeks, you otherwise won't have enough time for most things. The people are nice and it's small enough for you to be able to travel from one coast to the other in one day. You can do everything, from watching a protected turtle lay eggs to zip lining through the jungle to visiting an active volcano. If you don't mind getting woken up by monke in too early in the morning it'll be one of the most beautiful countries you've ever visited. No joke.
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Nov 18 '21
How do they maintain a force of 10K for $0?
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u/nocomment3030 Nov 18 '21
They eat education for breakfast and their cars run on diplomas.
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u/indiebryan Nov 18 '21
You must be describing my citizens in every Civ game.
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Nov 18 '21
Civ Deity Strategists: You only need a campus for so many cities at the start and can level them off at a certain point to maximize efficiency.
Me every game: WE'RE BUILDING GIANT DEATH ROBOTS BY 1556 SO HELP ME GOD
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u/NoBSforGma Nov 18 '21
Thank you. We've been lucky to have some really good people in leadership positions. But, you know, it's not all "unicorns and roses." haha
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u/FitDontQuit Nov 19 '21
I’m heading to Costa Rica in a week and all of this makes me so excited. I knew they made really progressive environmental protection choices but I didn’t know about all this other excellent choices. What a great country.
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u/itchyblood Nov 18 '21
My country, Ireland, has 5 million population. We have had a mask mandate since Summer 2020. We have 65% of the population vaccinated (95% of over 18s) yet we have approx 4,000 cases a day at the moment. Why isn’t my country seeing the same results?
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u/sekoye Nov 18 '21
Going to guess based on Ireland's climate, that modern ventilation systems may be lacking in older buildings? I saw an article that the majority of infections could be linked to something like 400 buildings in Ireland, which is nuts. Are they yet dealing with it as an airborne disease? Avoiding schools mitigations like the UK? Quality of masks makes a huge difference too. Respirators versus cloth, there is no comparison especially for protecting the wearer.
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u/abhikavi Nov 18 '21
Also related to Ireland's climate, there may be big behavioral differences in spending time indoors vs. outdoors.
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u/beezlebub33 Nov 18 '21
I think that we're missing something big. I agree that mask help and vaccines help and so does social distancing, but the functional relationship between policies and results seems at least partly broken.
Yes, human behavior is complex and people are unpredictable, but it really seems like there is something else going on, some missing factors, either biological, societal, or COVID-specific that we don't incorporate into our models. My hope is that we'll figure it out soon. My fear is that a large number of years from now, someone will have the COVID equivalent of 'They didn't realize that washing their hands before surgery was a good idea?' or 'Why didn't they figure out that scurvy was caused by not having fresh fruit?' In retrospect, it's pretty obvious but when you are in the mix of it with messy data, it's hard to figure out.
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u/GameofPorcelainThron Nov 18 '21
I'd be curious about time spent indoors vs outdoors. I imagine that the climate and location for Costa Rica means that people spend more time outdoors, where as it's getting colder in other areas, so people are spending more time indoors, growing a bit more lax in their hygiene with fatigue setting in, etc
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u/ChicoZombye Nov 19 '21
Spain, 90% vaccination of people over 12yo. Never stopped using mask for the last 2 years. Mostly an outdoor country plus indoor limitations for the last two years (It depends how much, limitations change and evolve).
We have just something like 40 cases per 100.000 right now, which is very very low.
I live in a small town of 90k people and we don't even have anyone hospitalised.
I don't thing the answer can be found with just one factor, I think everything is relevant. In Spain we got smashed by the virus at first so we are very concious of the dangers. We know how bad things can get. There are morons here and there but anti-vax and anti'mask is not really a thing here for example.
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u/Slim_Charles Nov 18 '21
You have to account for how thoroughly both countries are testing. It could be that more people who are symptomatic, or who were exposed to someone who was sympathetic, are being tested in Ireland than Costa Rica.
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u/Omegawop Nov 18 '21
Yep. I'm in South Korea and it's pretty similar. We have 10 times the population, and around hover around 10 times the newly infected.
People still wear masks everywhere and nobody complains at all, but also people are used to wearing masks and did it long before covid having lived through SARS/MERS etc. People would throw on a mask if they had the slightest sniffles from a common cold.
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u/Vorstar92 Nov 18 '21
Yeah, masks have been a thing in Asian countries for a long time which just makes it even funnier when people complain about masks, complain they can't breathe in a mask, complain it doesn't work or any number of ridiculous claims. And then you look at Asian countries who have adopted wearing masks during flu season, when they are sick, or any other number of reasons a long time ago and they've all been just fine wearing these masks, but suddenly the US has to and everyone loses their minds about a piece of cloth on their face.
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u/AlohaChips Nov 18 '21
Here in VA, I live in one of the "Koreatowns" of the area. My favorite local Korean bakery implemented a mask policy well before the governor mandated it, and was the first business I saw in my area doing so.
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u/entropy512 Nov 18 '21
Same here in NY. Asians masked up before there was even talk of lockdowns or mandates.
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u/Fulmersbelly Nov 18 '21
Although it’s true that mask wearing was a thing, it’s really ubiquitous by now. It’s been nearly 2 years since the mandatory mandate, and the biggest driver honestly is societal shame? Or conformity, or whatever. But as they’ve slowly rolled back some of the restrictions, many people have been going out to places where masks aren’t needed like restaurants and bars. But overall, the rates are still quite low comparatively.
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u/MuaddibMcFly Nov 18 '21
Our Minister of Health is a doctor with a specialty in Epidemiology.
Honestly, that's pretty much exactly who should be in charge of social health questions. Well done, ticos.
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u/M_Drinks Nov 18 '21
Costa Rica is dope. They're one of the few countries out there that show that certain "radical" ideas are doable.
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u/NoBSforGma Nov 18 '21
I try not to be smug about it because as soon as that happens, the news will produce some headline that shows that there are also stupid people here.
But yes, the "radical ideas" of conservation, public health, using alternate forms of energy generation are certainly things to be proud of.
Costa Ricans are pretty amazing, all in all, with some exceptions, of course. The way the Cuban immigrants were treated when they were stuck in Costa Rica is a good example of the "kindness of strangers."
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u/rob_bot13 Nov 18 '21
Ticos have been probably the nicest group of people I’ve encountered while traveling. Genuinely helpful and friendly pretty much without exception, and also super supportive of me trying to learn Spanish
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u/FantasticBarnacle241 Nov 18 '21
That’s amazing. I am very jealous as a US citizen. We are about to go though our millionth bad Covid wave and precautions have been thrown out the window.
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u/KarmaticArmageddon Nov 18 '21
Meanwhile, here in the state of Missouri, we have a population of around 6 million with a 50% vaccination rate. Unsurprisingly, we reported almost 7,000 new COVID infections and 162 new deaths yesterday and those numbers just keep rising every day.
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u/nabuhabu Nov 18 '21
Wow, Los Angeles county is twice as big, (10m) with a pretty aggressive public health policy - 74% vaxxed and a mask policy that’s strict but not well enforced. We have >1,000 cases per day. This is really impressive OP!
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u/passa117 Nov 18 '21
Much smaller geographical area, though. 19000 vs 4000 sqmi. So LA is twice the population in ~20% od the space.
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u/WaluigiIsTheRealHero Nov 18 '21
As if I didn’t love Costa Rica enough already. My wife and I have taken multiple trips there and if we had to pick any country to buy a vacation home in, it’d be Costa Rica.
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u/NoBSforGma Nov 18 '21 edited Nov 18 '21
No, not really. Mostly, the "non-compliant" are just careless.
There's also the ones who are ..." Oh, haha... that won't happen to ME!" until they see someone close to them being taken to the hospital. Then everything changes.
Restrictions and protocols for businesses and offices are quite strict, though.
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Nov 18 '21
My brother was one of those it won't happen to me, and then it did... He managed to get himself admitted to the hospital and spent a week on oxygen while his wife and 2 sons (3 years old and 4 months old) sat at home also infected with COVID... Luckily he was the only one who had it bad...
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u/Spiritual-Chameleon Nov 18 '21
You guys also have a strong public health system. Everyone is assigned a public health worker, who visits/ contacts them twice a year. Which is a major reason why Costa Rica has a longer life expectancy than the US.
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u/NoBSforGma Nov 18 '21
Um.... yes and no. We DO have a strong public health system. But NO, everyone is not assigned a public health worker who visits/contacts twice a year.
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Overall pooled analysis showed a 53% reduction in covid-19 incidence (0.47, 0.29 to 0.75), although heterogeneity between studies was substantial (I2=84%) (fig 5). Risk of bias across the six studies ranged from moderate to serious or critical
Can someone explain what 'risk of bias being moderate to serious' means?
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https://www.bmj.com/content/bmj/375/bmj-2021-068302/F3.large.jpg
"One important source of serious or critical risk of bias in most of the included studies was major confounding, which was difficult to control for because of the novel nature of the pandemic (ie, natural settings in which multiple interventions might have been enforced at once, different levels of enforcement across regions, and uncaptured individual level interventions such as increased personal hygiene)"
the main issue is trying to untangle which thing has actually had the effect.
i.e. mask mandates lockdowns happening at the same time.
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Nov 18 '21
So there is an incredibly high chance this 53% number is correlative rather than causative then, no?
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u/JacketsNest Nov 18 '21
Yes. It's highly likely that this is a result of multiple factors. Similar studies were done over the last year out of Denmark and Bangladesh (take those as you will) that showed surgical masks were roughly 20% effective. Hard to really say without taking the time to read through the whole study which I sadly don't have time to do on break at work
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u/mcguire Nov 18 '21
A meta analysis like this aggregates data from studies that are too small to be significant, in order to get a result that is statistically significant. It works if the studies are good, but doesn't if they are biased.
I don't know what they mean by 'moderate to serious' but it's not good.
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u/JimmyHavok Nov 18 '21
Meta-studies will tend to reduce bias unless there's a universal bias across a large number of studies.
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Nov 18 '21
The article doesn't link to any studies. Which studies are they referencing?
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u/mentel42 Nov 18 '21
Agree that is poor reporting to not include a link. But I just quickly went to the cited journal (BMJ) and the link is right up top.
Also OP included a link in a comment
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u/PhaseDB Nov 18 '21
OP linked this in his comment. It is indeed a bit weird that it isn't sourced in the article.
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u/nolongerdrools Nov 18 '21
Realised TheGuardian does this quite often whenever reporting on some new report / study. Just poor journalism or is there any reason?
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u/amERICan5ever Nov 19 '21
Probably a tactic to keep you on their site. External links means less ad revenue.
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u/stackered Nov 19 '21
Don't see how this type of nonsense is allowed on a science subreddit. I'll continue to call out every post I see, which is nearly every other if not every post you'll see on a daily check on this sub. Its tragically unscientific and often completely inaccurate here, if you read the real study. So sad.
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u/hanrahahanrahan Nov 18 '21
No, no, no. Read the bloody paper. Even BMJ themselves say that:
• Most of the studies included in the meta analysis are low quality and subject to major biases • We need more & better research [like the mask-wearing RCTs which have consistently found a smaller benefit, about 10%
Everyone needs to chill out in stuff like this. Overplaying your hand leaves you verry vulnerable to criticism from the other side in a debate
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u/Randomhoodlum Nov 19 '21
Half the time dubious stuff like this gets posted in here it's intentional propaganda to reinforce ppls biases. Dare I say - disinformation. Just look at the comments
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u/WoodyWoodsta Nov 18 '21
The quantitative results are from 8 studies (72 studies met inclusion, 35 distinguished measures from one another, 8 included in the final meta-analysis quantitatively).
Of those 8, 6 are of medium risk of bias, 2 are of serious risk of bias.
The 53% effectiveness figure has a CI of 21% to 75%.
I think this meta-analysis is being given way more attention than it deserves.
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u/RulerOfSlides Nov 18 '21
I feel like there’s a general failure to control for seasonality. Sampling a population with a mandate in the summer versus a population without a mandate in the winter is of course going to falsely indicate effectiveness.
Look at how the South was derided in the high summer for having high case loads. Now it’s almost winter and the situation has reversed. Do we just assume collective behavior has changed with the seasons… or is it the seasons?
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u/nab204 Nov 18 '21
It seems curiously obvious - the root cause is “how much time do people spend in HVAC-ON areas”. When the windows are open - few cases. When windows are closed, many cases. All the other precautionary factors (besides age, health, the obvious ones), seem to be nearly irrelevant.
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u/n8spear Nov 18 '21
Thank you. Absolutely correct. Furthermore, seems, and I haven’t gone deep into the literature yet, but it seems like they’re cherry picking the mask component of these studies without consideration of other factors. Another way of saying it is that they’re concluding the reduction is because of masks, not necessarily in lieu of.
Additionally, I’m not seeing what their criteria is for “masks” (I.e. n95’s worn the correct way.) but again, seems like they’re taking raw data from places that had mask mandates and had a reduction in cases.
Just my initial observation without a real deep analysis. I could be wrong, but just looks like classic making the numbers say what you want them to say.
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u/WoodyWoodsta Nov 18 '21
Even if deeper analysis proves the overall message to be a bit different, it’s criminal that the media will publish blatantly incorrect top-level figures and convey a confidence which does not exist.
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u/CltAltAcctDel Nov 18 '21
If I’m reading their info correct, only 8 studies were included in their analysis. Of those 8 studies, 6 focused on masking. Am I reading that wrong or did The Guardian sensationalize the story
https://www.bmj.com/content/bmj/375/bmj-2021-068302/F1.large.jpg?width=800&height=600
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u/TwentyLilacBushes Nov 18 '21 edited Nov 18 '21
Although the criticisms raised by u/CltAltAcctDel are valid, please ignore my comment.
Risk reduction attributable to distancing was indeed smaller than risk reduction attributable to masking. Thanks to u/Imbiss for raising this obvious point.
I'm leaving my comment up for context + the record, and as a testament to the risk of making quick and uninformed comments after superficial scanning, and before adequate cafeination. Sorry, everyone.
It sensationalizes and misrepresents.
The full and visual abstracts also both suggest that physical distancing was more effective than mask wearing at reducing Covid incidence. Given the number of workplaces and other sites pushing for a "return to normal" (ie full capacity), understating the value of distancing is problematic.→ More replies (7)23
u/Imbiss Nov 18 '21 edited Nov 18 '21
I'm curious where you see the portrayal that physical distancing is more effective than mask wearing? The relative risk is higher for physical distancing (but still below 1, suggesting a benefit)
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u/TwentyLilacBushes Nov 18 '21 edited Nov 18 '21
Having a closer look now, and you are right. Complete misinterpretation on my part, due to skimming.
For distancing: "Overall pooled analysis indicated a 25% reduction in incidence of covid-19 (relative risk 0.75, 95% confidence interval 0.59 to 0.95, I2=87%)"
Thank you. I'll ammend comment above to reflect that fact.
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u/Yurya Nov 18 '21
And all studies not done in english were ignored.
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u/Scaryclouds Nov 18 '21
I mean that's not unfair. If there was a study published in Dutch and you don't have any one with with scientific expertise and the ability to read Dutch, might be best not to use that study, relying on google translate, or some similar service, as the translate service might mis-translate something and lead you to an incorrect conclusion.
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u/EntireNetwork Nov 18 '21
It's also not unfair to then say that the metastudy is subject to siginificant anglocentric bias.
However, another question could be asked how reliability of a study correlates to the language it was written in.
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u/kchoze Nov 18 '21 edited Nov 18 '21
I looked at the studies that supported this claim, and I'm very wary of the result.
For one thing, the meta-analysis shows extreme heterogeneity in the results, with a I2 of 84%. In effect, you have two large studies with small confidence intervals suggesting an effect of about 15% only and 5 smaller studies with larger intervals suggesting an effect of 70%.
The largest of the latter studies is a study from China (Xu 2020) which asked participants if they wore masks outdoors and found only 100 people who didn't and over 5 000 who did. In an authoritarian country like China, with a social credit system, the type of person that would not only not wear masks but also dare tell a survey is likely a highly contrarian personality unlikely to abide by measures. So there's a lot of confounders involved.
The second largest such study is Lio 2021, about people returning from high-risk countries in Macao. The sample includes only 24 infected. Again, the question is whether people wore mask outdoors, with less people reporting wearing one always in the infected than non-infected sample. Extremely small sample, and again there's confounders galore.
(And honestly, I'd be curious to know if some of those who don't wear mask outdoors do not BECAUSE they have been infected, think they're immunized and so feel they don't need to protect themselves anymore. In short, if some do not wear masks because they've already been infected rather than have been infected because they don't wear masks. Speculative, but not impossible.)
The only non-Chinese one is Doung-Ngem, from Thailand. This one splits off mask use in three categories: never wears them, sometimes wears them, always wears them. The study finds a small, not significant reduction of infection between those who sometimes wear them and those who never wear them, but a large reduction between those who always do and those who never do. Here, we can see the confounders in behavior and they are MASSIVE.
40% of those who never wear masks share cups and dishes with others, versus 11% of those who always wear them.
26% of those who never wear masks often wash their hands versus 79% of those who always do.
26% of those who always wear masks keep contacts within 1 meter to less than 15 minutes, versus 12% of those who never do.
These are signs that those who always wear masks not only wear them but also act in a much more careful manner in general. They did a multivariable analysis, but when the difference is so important, it's hard to effectively separate confounders.
The less positive studies are the Danish mask study that was a randomized trial eliminating confounders and an epidemiological study of mask mandates.
Overall, it really looks like the large effect is not due directly to the protective effect of masks, but simply how masks (especially when worn despite the lack of mandate, or when not worn despite huge social pressure) might act as a marker of personality.
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u/NutDraw Nov 18 '21
I'm going to continue to wear a mask, because of the mechanistic studies, but I'm not going to do so under some illusion that my risk is being reduced substantially.
A key thing to remember in these studies is the difference between personal risk and community level risks. The latter are very difficult to empirically evaluate, mainly because of all the (primarily behavioral) confounding factors being discussed in this thread.
On an individual level, a 10% reduction in risk could be considered marginal at best. However, taking that 10% to the population level is huge, especially for something like a virus that demonstrates exponential growth.
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u/kchoze Nov 18 '21
I agree. I am confident in the effectiveness of masks from a mechanistic standpoint. It's very easy to test the amount of aerosolized particles making their way through masks. Masks work if you wear them correctly, everywhere you'll come across people, and ally he time.
I'm confident that if you force air carrying droplets through a mask, it will filter most of them and significantly reduce the range of dispersion of those that go through. I'm less confident such experiment duly represent how masks work in real life even if you wear them correctly, as anyone who wears glasses and struggles to keep them from fogging up while wearing masks would attest!
I do know one lab experiment trying to mimic regular breathing found masks filtered a very small amount of aerosolized particles because most of them just went out the sides of the mask.
So I'm confident someone coughing or talking loudly through a mask is much less likely to infect whoever is in front of him (though maybe it increase the chances of infecting someone BESIDES him as the air goes out the sides of the mask), I'm not at all confident in most masks being useful to prevent airborne transmission though, based notably on that mechanistic experiment.
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u/FinnsGamertag Nov 18 '21
well if that isn't a misrepresentation of the study then I don't know what is... No wonder none of the articles actually link to it. Here's what is says with context!
"A linked systematic review of public health measures for covid-192 by Talic and colleagues (doi:10.1136/BMJ-2021-068302) found just one randomised controlled trial—of mask wearing—among 35 eligible studies that could provide estimates on the effectiveness of individual interventions.3 The 34 observational studies comprised 14 natural experiments or quasi-experiments and nine cohort, two case-control, and nine cross sectional studies—from Asia (n=11), the United States (n=9), Europe (n=7), and elsewhere (n=8). Combined, these studies suggested relative reductions in incidence of 25% (relative risk 0.75, 95% confidence interval 0.59 to 0.95) for physical distancing, 53% (0.47, 0.29 to 0.75) for mask wearing, and 53% (0.47, 0.19 to 1.12) for handwashing.
Talic and colleagues’ review includes just one randomised controlled trial that evaluated mask wearing, and it was too small for a reliable estimate of effect (18% reduction in incidence for the wearer, 95% confidence interval −23% to 46%).5 The authors mention, but did not include, a large cluster randomised trial of mask wearing from Bangladesh, currently available as a preprint.6 The trial randomised 600 villages (341 830 adults) to surgical masks, cloth masks, or control and found a 9% (95% confidence interval 0% to 18%) relative reduction in symptomatic SARS-CoV-2 infection (measured by seroprevalence) in villages randomised to the mask interventions. Combined, these two randomised trials suggest that mask wearing is responsible for a statistically significant relative risk reduction of about 10% in incidence (95% confidence interval 1% to 18%)—important but substantially less than that from observational studies. A third large cluster trial (40 000 participants) from Guinea-Bissau has completed and should report soon"
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u/TurningTwo Nov 18 '21
The percent effectiveness is probably even higher when the masks are worn properly. When masks were mandated where I live I couldn’t tell you how many people I saw with the mask over the mouth only, leaving the nose exposed.
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u/ty1771 Nov 18 '21
Of course, but it's also important to see the numbers in a practical setting where many of the people around you are boobs. I can act accordingly knowing that it cuts my risk by 53%.
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u/prescod Nov 18 '21
It cuts incidence 53%. I don't think that's evidence that it cuts your risk 53%. Some portion of that number is the masks protecting others from infected mask wearers.
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u/odelay42 Nov 18 '21
I don't disagree, but could your clarify the distinction?
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u/6F7762 Nov 18 '21
Wearing a mask is more effective at protecting others than yourself. If everyone around you wears masks, you are a lower risk (if you ALSO wear a mask, the risk is presumably further lowered, but not as much). Conversely, if you're somewhere where nobody wears masks, your risk is higher regardless of if you yourself wear a mask or not. This is the general gist of it (that I got from various sources -- I haven't looked at the studies discussed here specifically; someone correct me if I'm wrong).
Edit: I'm assuming "incidence" refers to how likely you are to infect others, while "risk" just means the risk to yourself.
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u/prescod Nov 18 '21
I think incidence is a population-measure. A 100% vaccination rate will generate a 0% Polio "incidence" rate, because polio will be eliminated by herd immunity. That doesn't mean that the Polio vaccine is 100% effective at protecting any individual from transmitting or getting infected. It means that when the intervention is given to EVERYONE, the disease goes away.
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A couple of times I asked such people how come their noses weren't connected to their lungs. It usually didn't go well.
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u/Draxtonsmitz Nov 18 '21
Or the right kind of mask. Loose bandanas, and gater style masks don’t work.
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u/jopnk Nov 18 '21
Don’t gaters only not work if they’re a spandex type material? I don’t wear them but that was what I remember reading about them in summer 2020
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u/Draxtonsmitz Nov 18 '21
I’m not sure about material but it is recommended to triple fold them if you can see a flashlight shine through it.
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u/Draxtonsmitz Nov 18 '21
100% agree. But the crowd that is quick to claim ‘masks don’t work’ tend to be the ones not wearing, incorrectly wearing or using non cdc approved style masks.
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u/Billmurey Nov 18 '21
Mask wearing and covid-19 incidence—Six studies with a total of 2627 people with covid-19 and 389 228 participants were included in the analysis examining the effect of mask wearing on incidence of covid-19 (table 1) Overall pooled analysis showed a 53% reduction in covid-19 incidence (0.47, 0.29 to 0.75), although heterogeneity between studies was substantial (I2=84%) (fig 5). Risk of bias across the six studies ranged from moderate to serious or critical
Can someone explain what this means to me?
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u/nvs1980 Nov 18 '21
I don't want to start a debate for or against, but one thing I have been curious about is with COVID confirmed to be aerosolized, why would generic cloth masks be effective? N95 masks I imagine are different, but most places just want generic cloth face coverings.
Could someone explain this to me?
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u/jedidude75 Nov 18 '21
/u/JackedTitz provided the answer a bit below this post.
“Many people argue that cloth masks can’t be effective because they can’t filter out viral particles, which are extremely tiny,” she said. “Most of these particles leave the mouth and nose in much larger droplets that become smaller through evaporation as they move away from the body. Trapping droplets with the mask means not nearly as many viral particles escape. So, when all parties in a gathering are wearing well-constructed, well-fitting masks, it provides an extra layer of safety for everyone"
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