Confused about the efficacy of masks
July 1, 2020 11:12 AM   Subscribe

Since COVID-19 "started" I've been confused about the efficacy of masks. I have read so many contradicting statements about the efficacy of masks (who they protect, who should wear them, type of mask etc.), that I am just totally confused. I'm hoping to ease my confusion and find concrete-ish answers!

Now, don't worry, I am not someone who is refusing to wear masks. I've acquired cloth masks for myself. I wear masks when stores require me to wear them, but if it's not required I tend not to wear one. My workplace is about to re-open to the public in a VERY LIMITED way and everyone is fighting about masks. Should we get customers to wear them, if we do should they be mandatory, who the mask protects (the wearer or the other person), the proper way to wear a mask, etc. It's gotten pretty intense.

What's confused me about masks (and frankly, has upset me in a way that is probably completely irrational) is the 180 from public health officials. I'm Canadian and we had Dr. Theresa Tam telling us that we didn't need to wear masks in March, reasons included the general concensus that people were too stupid to wear masks properly (constant adjusting, touching the mask, etc.) and that masks protect the people AROUND the mask wearer, but not the wearer. So if you're not displaying symptoms, you wouldn't need a mask.

I understand that public health officials told the public this in-part due to shortages of medical masks for healthcare providers (according to Dr. Fauci). And since late May, masks have been highly recommended by Dr. Tam. I guess with the 180 and all the confusion about WHO is protected... I actually feel pretty confused about masks and actually quite angry AT health officials. Again, I understand it was to secure enough masks for healthcare workers, but I'm sure more people would be open to wearing masks now if they hadn't been told they weren't effective in March!!!

So, my question is: What IS the actual efficacy of masks with regards to COVID-19? WHO are they protecting? The mask wearer? The people around the mask wearer? Both at some level? I would appreciate any good scientific sources, but I know that research about COVID-19 is changing constantly!! I really just want to feel less confused about masks, personally.
posted by anonymous to Health & Fitness (27 answers total) 17 users marked this as a favorite
 
With the caveat that all information is provisional:

*N95 masks seem to protect both the wearer and (if they don't have a vent) people around the wearer.

*Cloth masks seem to protect people around the wearer, plus maybe the wearer a bit.

There has been some evidence suggesting that if we had 100% cloth mask adoption, we could basically go back to "life as normal" because of the extent to which it would limit the spread of the virus.

I wear a cloth mask whenever there is a chance that I am going to come within 6 feet of someone who I don't share a house with. I've been very careful, but there is always the possibility that I'm an asymptotic carrier. I wear a mask because I care about public health, not because I think it will help me protect my health. If it turns out the studies are wrong about mask efficacy, then I've been mildly inconvenienced by having to wear a mask. If they are right, perhaps I've saved a life.
posted by Betelgeuse at 11:21 AM on July 1, 2020 [55 favorites]


COVID-19 is a disease that we now understand to be transmitted primarily, perhaps exclusively, by respiratory droplets. Preventing a portion of respiratory droplets from hanging around in the air around you helps to prevent other people from breathing in those respiratory droplets. Your mask only prevents you breathing in existing virus from the air by a few percentage points (say, 5%), but it prevents the respiratory droplets that you're breathing out from getting out into the air by about 70% or more.

The reason the recommendation changed is partly that we know more about the disease. Initially experts thought that it was more of a surface transmitted disease, and that people were getting it because they were touching their eyes, mouth and nose. The actual virus is pretty small, so it does exit your cloth mask, it's commonly found on the outside of the wearer's mask, rather than the inside. Also, there was, as you mention, the shortage of medical masks. It was deemed more important for healthcare workers to wear a mask around patients they knew were sick and the recommendation was for everyone else to just stay home. Also, some of original thinking was that if you promoted masks, then more people would leave their homes, and that staying away from other people was more effective. As the pandemic has worn on, the idea of habituating people to masks makes more public health sense.

Essentially, the efficacy of the mask as a measure of public and personal health maintenance was initially underestimated, but now it's considered substantially better than not wearing one.
posted by vunder at 11:28 AM on July 1, 2020 [30 favorites]


Since you asked for studies:

Here is a meta-analysis of mask and respirator wearing, including pointing to my point about cloth masks being effective for limiting the spread to other people: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7191274/

Here's a pretty good post from just a few days ago that brings together a lot of the studies: https://www.ucsf.edu/news/2020/06/417906/still-confused-about-masks-heres-science-behind-how-face-masks-prevent
posted by Betelgeuse at 11:30 AM on July 1, 2020 [10 favorites]


This is an article from June 26 by a UC San Francisco health journalist who interviewed two USCF epidemiologists on the same types of questions you're asking. It covers why masks weren't recommended early on, studies on how much masks prevent spread of respiratory droplets, evidence that cases have slowed down in cities that mandated mask-wearing, case reports where people who were sick with the virus avoided infecting others because they were wearing masks, how many people should wear masks, and differences between mask types.
posted by capricorn at 11:32 AM on July 1, 2020 [10 favorites]


Ahh, jinx, Betelgeuse!
posted by capricorn at 11:32 AM on July 1, 2020 [1 favorite]


There was another recent meta-analysis on this topic in the Lancet, a top journal, that found significant protection for masks.

There is a second meta-analysis by the Institute for Health Metrics and Evaluation (IHME) at the University of Washington that's reviewed in lay terms along with the first meta here:

"Our analysis of all respiratory infections and mask effectiveness suggests a reduction in infection for mask-wearers by at least one-third compared to control groups. This work supports the growing scientific consensus that cloth masks, whether homemade or commercial, can reduce respiratory virus infections by 33% and slow community spread of COVID-19."

They incorporated mask use into their predictive models and state:

"The US has had over 120,000 deaths so far. By October 1, 2020, cumulative COVID-19 deaths could reach 179,106 deaths (with an estimated range of 159,497 to 213,715). In terms of the mean projection, this represents approximately 60,000 additional cumulative COVID-19 deaths between today and October 1, 2020. That number drops to 146,047 (with a range of 140,849 to 153,438) if at least 95% of people wear masks in public. In other words, if 95% of the US population always wore masks in public, more than half the deaths that are predicted between now and October 1 would be avoided."

I think the initial discouragement around mask use was mostly about not having evidence for their benefit outside of medical settings (which we have now) in addition to trying to reserve PPE for medical workers as you note.
posted by quiet coyote at 11:36 AM on July 1, 2020 [5 favorites]


There's also a nice review of the evidence as of 10 days ago here.
posted by quiet coyote at 11:39 AM on July 1, 2020 [1 favorite]


Back in March, the discussion was primarily about whether or not masks would protect the wearer. This is why you saw people arguing against masks by pointing out that people will fiddle with their masks, putting them more at risk.

Since then, we've learned more about how the virus spreads:

(a) We now know that respiratory droplets are the most important way that the virus spreads, rather than touching your eyes, mouth, nose etc

(b) We now know that there are many more asymptomatic carriers than previously believed

The recommendation to wear masks now is primarily about keeping you from spreading your respiratory droplets around. It does protect you somewhat but the biggest benefit is protecting other people.

I think it is really unfortunate that we were told not to wear masks early on, but I think that your anger is misplaced. This is a new disease - it's inevitable that public health guidance will change as we learn more about it, because it really is a numbers game that depends on details about transmission we don't always know yet. You should be the most angry at people who are exploiting the change in advice to encourage people to ignore current advice, promote conspiracies, etc.
posted by Kutsuwamushi at 11:41 AM on July 1, 2020 [58 favorites]


One other thing to note regarding your frustration about early messaging is that masks didn't HAVE to be part of the conversation- it's a result of other failures to contain the virus. For example, Iceland is in great shape because they built up testing and contact tracing, and they never needed to push mask use in any way.
posted by quiet coyote at 11:44 AM on July 1, 2020 [5 favorites]


I mean, Iceland is also an island with a population about the size of Cleveland's and the lowest population density in Europe. Testing and contact tracing is great, but they had a ton of other factors going for them.

Another reason health officials advised against mask wearing early on was they were concerned that people wearing masks would be less inclined to social distance (like, they would feel like the mask was keeping them safe); in fact face coverings seem to be more effective than social distancing (so if you could only do one or the other, masks would be preferred) and also people who wear masks don't seem to be any less inclined to social distance.
posted by mskyle at 12:14 PM on July 1, 2020 [10 favorites]


If more Americans wore masks the pandemic would slow, experts say (Guardian, Jun. 30, 2020, "More than 30,000 deaths could be avoided by October if 95% of Americans wear face masks in public, according to research by the University of Washington. [...] “Masks are incredibly important,” said Krystal Pollitt, an assistant professor at the Yale School of Public Health. “The airborne transmission of the virus is increasingly of concern and masks are an effective way to prevent that. The more we learn about this virus, the more I’m encouraging people to wear masks.”")

Spate of new research supports wearing masks to control coronavirus spread (WaPo / reprint, Jun. 13, 2020, "Several new studies published this month support wearing masks to curb the transmission of the novel coronavirus. The broadest, a review funded by the World Health Organization and published in the journal Lancet, concluded that data from 172 observational studies indicate wearing face masks reduces the risk of coronavirus infection. [...] Face masks appear to be most effective when supplemented with hand-washing and physical distancing, [the author of the review, Holger Schünemann, an epidemiologist and physician at McMaster University in Ontario,] and his colleagues said.")
posted by katra at 12:46 PM on July 1, 2020 [1 favorite]


Stepping back a bit, the reason for the confusion was that while we have a good understanding of viruses, our species has never dealt with epidemiology on this scale before. Talking to an acquaintance who is a statistician in the field, she told me that there were previously hundreds if not thousands of models proposed for how to handle a global pandemic -- in fact it was sort of a joke as a fallback thesis topic -- and 99% of those models have been now been proven wrong.

The models all contain(ed) a large number of decision points concerning how the pandemic spread, and what the geopolitical situation was, and how much people would comply safety precautions, etc. And that last one, of course, includes: how many countries could afford masks, would people wear masks, would they wear them correctly, would the masks be effective, and how long would people wear them before giving up.

Faced with all those questions and without real data the Powers That Be were forced to make a guess, and they guessed wrong.

As time has gone on we've been able to work with actual data rather than following a model some grad student produced in 1975. The information has been getting better and more reliable as time goes on for the simple reason that we have actual experience now, so following the latest recommendations is a good way to go.
posted by Tell Me No Lies at 1:53 PM on July 1, 2020 [18 favorites]


A salient detail I recall from one of the published papers: if you talk to somebody then the air droplets you expel can travel for a couple of metres, if you cough, about 4 metres, if you sneeze up to seven. After you have moved on the really small air droplets can hang around in an indoor space for half an hour or so - then they land on surfaces. Masks greatly help prevent all that.
posted by rongorongo at 3:10 PM on July 1, 2020 [1 favorite]


I'm Canadian and we had Dr. Theresa Tam telling us that we didn't need to wear masks in March,

A lot of people are struggling with changing recommendations, but here's some information that may help:

1. Health professionals didn't know a lot about COVID-19 in March.

2. Recommendations were based partly on the shortage of PPE. People were already rushing out to buy stuff and creating shortages for health care workers.

3. The assumption was that COVID-19 was like SARS and MERS (which are also coronaviruses) - that the viral load builds slowly, and is at its peak when people are most sick. Which is to say - that there's not a lot of asymptomatic transmission. But we found out with COVID-19 that there's a TON of asymptomatic transmission. Shit.

4. It's hard to give broad, accurate recommendations in a health crisis. You have to balance scientific accuracy with clarity, trustworthiness, good reasons, and a ton of other considerations. A lot of health professionals didn't have the support from political leaders to do this the right way.

5. Some health professionals and political leaders fucked up and said some bullshit in order to justify why they said that they weren't recommending widespread masking.
posted by entropone at 3:21 PM on July 1, 2020 [4 favorites]


A lot of people who promoted the use of masks from the start have heavily criticised the initial official recommendations against mask-wearing (for various reasons), and suggested that it took far too long for the advice to change -- and to some extent they may have a point. But mostly, as others have said, we genuinely have a better understanding of how the virus spreads now, and on the basis of that information it now seems clear that ubiquitous mask-wearing == good, actually.

We know more about the relative risks of transmission (droplets >>>>> surfaces), we know for sure that there are asymptomatic carriers, and we have case studies of specific incidents in which groups of people were infected (or not infected) in particular ways.

As someone who was staunchly on Team Masks Are Dumb in March, because that's what the official advice was at the time, I am also annoyed -- but I understand that sometimes we have to guess and sometimes we guess incorrectly. We should be following the latest advice.
posted by confluency at 3:34 PM on July 1, 2020 [2 favorites]


What's confused me about masks (and frankly, has upset me in a way that is probably completely irrational) is the 180 from public health officials. I'm Canadian and we had Dr. Theresa Tam telling us that we didn't need to wear masks in March, reasons included the general concensus that people were too stupid to wear masks properly (constant adjusting, touching the mask, etc.) and that masks protect the people AROUND the mask wearer, but not the wearer. So if you're not displaying symptoms, you wouldn't need a mask.

In addition to what has been shared above about evolving understanding of the disease (which is extremely on point), I observed that there was a light bulb that went off specifically around cloth masks in late March/early April.

Prior to that, the understanding was that if you weren't wearing an N95 style mask that had a fine enough filter to keep the virus itself out, or if you were wearing an N95 with a poor seal, you might as well not be wearing a mask at all.

Since then, research (including, I presume, the research linked above) has shown that this understanding was wrong: cloth masks help a whole lot by preventing dispersal of the virus. In other words, they may not filter out every little viral particle, but they keep it from flying so far through the air, which makes a big difference.
posted by billjings at 6:15 PM on July 1, 2020 [4 favorites]


I thought this was a great, down-to-earth explanation from a doctor of why we now think masks matter -- "It's the air you share." It really changed how I think about transmission of this virus.
posted by selfmedicating at 6:27 PM on July 1, 2020 [5 favorites]


In addition to what has been shared above about evolving understanding of the disease (which is extremely on point), I observed that there was a light bulb that went off specifically around cloth masks in late March/early April.

There was no 'evolving understanding' on masks. Respiratory infection = masks. This has been known for centuries. Epidemiologists have ZERO basis for claiming ignorance of this. They were trying to cover their own asses and it cost and is still costing thousands of lives. And that 'light bulb' going off? That was thousands of New Yorkers dying, including friends of mine and a neighbor in my building.
posted by sexyrobot at 7:17 PM on July 1, 2020 [6 favorites]


Oh, and as far as efficacy of masks...there was a paper on the blue that puts it in the ballpark of 3-4 million lives saved so far (ie 10s of millions of cases averted). And there was no massive outbreak from the protests...with millions of people...all wearing masks, and not even good ones in most cases. Nearly total effectiveness. Open bars with no masks, instant outbreak. You do the math. Even shitty masks are effective at thwarting this thing...as long as you make sure to cover both nose and mouth.
posted by sexyrobot at 7:23 PM on July 1, 2020 [2 favorites]


A lot of westerners looking at mask wearing were applying an unnecessarily tough efficacy standard to masks. Treating it like any imperfection in your mask wearing means you might as well not be wearing any mask at all, like touching your mask makes it useless, like a gap (or surgical mask) won't do anything.

This was a natural thing to port over from the medical environment where you might wear masks in a case of known infection risk. If you are intubating a series of covid patients all day, let's say 10 exposures, and your mask is 90% effective, that sounds like a lot... But 0.9^10 = only 34% chance you get through today uninfected. 2/3 chance of getting it. Do it again tomorrow and the next day, and your 90% mask might as well not be there. So they have a LOT of technology and processes in place to get their masks to be 99.9+% effective.

On a population level, you don't need anywhere near that level of effectiveness, because we're not swimming in a sea of virus all the time. But the need for those extreme levels of protection in a medical infection control setting means we had trained all of our doctors and nurses that REAL infection control is a, b, c and nothing less, and if you reuse your mask or air can get in around the sides then you've failed and will get the illness, and so people were just totally disbelieving that a CLOTH mask or a surgical (not sealed) mask could matter at all.

Plus I remember back in March everyone was saying that there was no asymptomatic transmission and everyone who had transmitted had symptoms, even if they were mild ones. That piece of information has definitely been revised!
posted by Lady Li at 9:25 PM on July 1, 2020 [18 favorites]


To be honest, as an Asian in Canada who's been vigilantly following HK/Japanese/Chinese media since news of the coronavirus emerged in December, it's mind boggling to me that there was so much foot dragging about whether masks could help in Western countries.

We knew from January COVID was very similar to SARS when the genetic sequence was published - transmitted through respiratory droplets - Hong Kong adopted mass masking in 2003 against SARS which worked, and people in HK, Taiwan, China, Korea, Japan etc. immediately masked up, even before governments told them to. Compliance is probably around 90-100% in these places, and case counts and deaths are starkly different despite the lack of strict lockdowns (all the regions above except China never had lockdowns and are very densely populated). Experts in Asia rang the alarm bells early on - I can only conclude that their recommendations were ignored by the WHO, CDC and the rest of the scientific establishment due to a blend of Western-centrism/language barrier/racism.

A lot of Asian people in other countries started wearing masks too, but that often invited unwelcome attention, especially before official recommendations changed in March.
posted by monocot at 10:47 PM on July 1, 2020 [9 favorites]


Oh, yeah, don't understate the impact of "culture" and western-centrism here, as monocot and others have pointed out. Wearing masks to reduce disease transmission is bog standard in much of the world. But here in the US they aren't often seen except as specialized medical equipment, and it was really easy for not only the American establishment but many Americans to dismiss widespread mask-wearing as just a weird foreign superstition.

This was made worse I'm sure by the blamey tone coming from the top with regards to China. There were a lot of cultural pressures in the US pushing for establishing Western superiority, rather than being open to the idea that Asia had experience dealing with these kinds of viruses recently and we might have something to learn. Science has always been influenced by culture and biases, sadly, and this is only going to be more true when the body of evidence is smaller and you can fit more possible hypotheses to it.
posted by Lady Li at 11:42 PM on July 1, 2020 [3 favorites]


...The assumption was that COVID-19 was like SARS and MERS (which are also coronaviruses) - that the viral load builds slowly, and is at its peak when people are most sic

Following on from this - and also from Lady Li's point on culture: It may well have been that the infection profile of SARS and MERS differs from COVID-19 with respect to asymptomatic transmission - but all 3 types of coronavirus can be transmitted by air droplets in the same manner. Places like Hong Kong, that had experienced SARS, drew lessons from this outbreak in terms of wearing masks in public places and taking people's temperatures as a pre-requisite to public space access. These habits persisted since the days of SARS. Many Western travellers would ask why the locals were wearing masks on the assumption that they were just paranoid individuals afraid of picking up a bug - rather than people who had/thought they had an infection and who would have been ashamed of passing it on.

The SARS avoidance strategies - which had worked so well before - were ramped up as a natural reaction when Covid-19 arrived. The temperature taking thing was probably not so effective (although it would have prevented some people from going into public indoor spaces when they were not feeling well) - but the mask wearing was. Countries that were threatened by MERS and SARS have done better at controlling COVID, on the whole (consider the population density of Hong Kong - and particularly the number of multi-generational families living in small apartments - with a population of 7 million they have had only about 1,200 cases and 7 deaths to date).

Importantly - and as stated above - the populations of these countries were used to the idea of wearing a mask to protect others from their own infections - rather than to prevent the wearer from catching infections in the environment - which is how they were always employed in the West.
posted by rongorongo at 5:21 AM on July 2, 2020 [6 favorites]


Terrific explainer from Erin Bromage, infectious disease guy. Previously.
posted by j_curiouser at 8:58 AM on July 2, 2020


... we had trained all of our doctors and nurses that REAL infection control is a, b, c and nothing less, and if you reuse your mask or air can get in around the sides then you've failed and will get the illness, and so people were just totally disbelieving that a CLOTH mask or a surgical (not sealed) mask could matter at all.

Hello! I am a nurse and I was one of those people!

I can't overstate how much of my training in infection control focused on preventing myself from becoming exposed or infected so that I didn't then go on to expose or infect my other patients.

Imagine a hospital ward with 30 patients. Imagine that three of the 30 patients require expanded infection control precautions due to C. difficile or influenza or lice or MRSA or TB or what have you. Imagine there are six nurses on the unit, so each nurse is assigned five patients. (Five or six patients per nurse in a non-ICU setting is a very normal patient assignment in most places in the US.)

With simple math it becomes clear that some of those nurses will have to care for a mix of patients--some on standard precautions, some on expanded precautions--and will need to go in and out of each patient's room multiple times throughout her shift to provide care.

The patients almost never have any direct contact with or exposure to each other, so we very rarely have to think about preventing them from infecting each other. WE are the potential problem, and our training and our PPE is chosen with one thing in mind--preventing ourselves from becoming vectors.

We're trained in the difference between the types of precautions necessary for various diseases, and in rigorous processes for putting on and taking off PPE in order to avoid accidentally contaminating ourselves. We exercise not-small amounts of self-restraint to avoid touching our masks and we wash our hands assiduously countless times a day. Because here's the thing--if we use our PPE wrong, we are risking people's lives. If we fail to prevent ourselves from becoming vectors, we cause harm to our patients.

So yeah, in the beginning when people suggested that wearing cloth face coverings could be beneficial, we were dubious at best. No one was really sure how covid was being transmitted--was it droplet or airborne? Only a properly-fitted, single-use N95 that is donned and doffed correctly is going to keep you from contracting an airborne illness, and only surgical masks that are FDA approved and thus fluid-resistant are going to protect you from droplets.

Things like physical distancing, staying at home, and hand washing made perfect sense from an infection control standpoint, but the idea that putting a bandana on someone's face made them less likely to contract covid seemed frankly unhinged.

We were thinking about how to avoid GETTING covid, and it remains true that a cloth mask isn't going to cut it if you're in sustained close contact with infected people who aren't themselves wearing a face covering.

Because most of us aren't epidemiologists we weren't thinking about how to avoid SPREADING covid population-wide, which is where a cloth mask IS useful in conjunction with physical distancing, testing, and contact tracing.

So please, please do wear a cloth mask whenever you're indoors in a place that isn't your own home and whenever you're outdoors and can't maintain physical distancing. Please.
posted by jesourie at 1:24 PM on July 2, 2020 [25 favorites]


Well, it comes down to glass half empty/ half full, doesn't it? If any reasonable sort of mask reduces the likelihood of contagion or transmission by 30-70 percent, well, a vaccine with those numbers is considered a successful vaccine.
posted by Chitownfats at 7:47 PM on July 2, 2020 [1 favorite]


Ottawa Public Health posted the following on Facebook today. It deals with the 180 advice change, specifically.

MANDATORY CLOTH MASKS: A Very Long Post. Please read to the end.

Public Health is about following evidence, so when we call for change, that change is the result of what our evidence is telling us. Lately evidence has been coming at great speed & volume.

We've been doing our best to keep you informed, but some of you may feel like in March & April we said cloth masks weren't needed, then in May & June said cloth masks were needed, & now we're saying they’ll soon be mandatory. We know this may have seemed confusing, and we're sorry about that.

However, each shift was evidence-based. Before we knew about asymptomatic transmission, there was no need for you to wear a cloth mask unless you were sick. Then evidence emerged to support its existence. We needed to react quickly, so we asked you to wear cloth masks when distancing was difficult to protect those around you.

We are once again in a period of change. The emerging evidence shows us that wearing cloth masks in indoor public spaces is a necessary measure to help keep our community safe; especially as we all begin gathering again. We know that this transition won’t be easy for you.

There will be bumps in the road as we work w/community partners to implement this measure. Some of you may have a hard time adjusting, and that’s ok. We’re all human, and none of us are perfect, but we will make this work. We know this isn’t easy for you, and we understand.

Just know that we care. We really do. We’ve been at this for months now, working tirelessly to try to keep pace with COVID-19 and keep you safe. Can we guarantee that things won't shift again? No. Can we guarantee that this measure will put an end to COVID-19? Also no.

But we can say this: we will beat this. We will keep following evidence & working together. We've said it 100 times: We are in this together. Thanks for sticking with us, Ottawa. You can read today's special statement about mandatory masks here: http://ow.ly/wNcF30qW0Hl

posted by If only I had a penguin... at 9:50 PM on July 3, 2020 [2 favorites]


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