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Here’s yet another estimate of how good different masks are

Published on 38 Comments on Here’s yet another estimate of how good different masks are

The CDC has a new study out that measures the efficacy of different kinds of masks. Here's the infographic:

Using our estimate that masks are equally effective at inward and outward protection, I converted this into one of the tables that I posted a couple of weeks ago:

This is very much in the same ballpark as the earlier estimates. The CDC is a little more bullish about surgical masks, and their estimate for N95 masks is somewhere between the previous estimates for fitted and unfitted masks.

In any case, everyone agrees on the basic hierarchy: N95 is best, surgical is next, and cloth is weakest. But all of them are better than nothing.

38 thoughts on “Here’s yet another estimate of how good different masks are”

  1. damgo2

    This is not actually a very useful study. What it actually found is more like "people who care about avoiding Covid get Covid less." The issue is that people who wear masks regularly are more concerned and careful about Covid in general.

    It's good to know that being careful works pretty well. But there's no way here to disentangle how much of the effect is due to masks and how much is social distancing, minimizing group socializing, avoiding crowded indoor spaces, etc.

  2. Solarpup

    The best mask is still going to be the most protective one that you can wear properly. I'll take someone wearing a cloth mask fully covering mouth and nose over someone with an N95 hanging off their chin any day.

    I've found a brand of KN95s that's comfortable, doesn't usually fog my glasses, doesn't slide around or slip off my nose, so that's what I'm running with.

    I'm about to go grocery shopping with my wife. I'm expecting to see a lot of uncovered noses in the grocery store, and those folks might as well just stop the pretense and go maskless.

    1. Salamander

      Which brand of KN-95 is that? I've had so much trouble with fogging that I have to shop with my glasses off, which isn't the optimal way to do it.

        2. Citizen99

          I've discovered the absolutely foolproof way to prevent fogging your glasses: a piece of paper tape (available at pharmacies) on each side of the nose applied to close the gap between the mask and your face. If you don't press it down too hard, it's pretty easy to pull the mask off, leaving half of each tape still attached to the mask, and it lasts for a good 4 to 6 uses before you have to replace the tape. It saves you from having to keep squeezing the metal insert down over and over, which never actually works very well.

      3. Solarpup

        My wife is the one who's been buying the KN95s from Amazon, so I'm not sure the brand. I know that's not particularly helpful, since they sell dozens and dozens of brands.

  3. Citizen99

    I agree with the above comments, especially Solarpup. I wear a cloth mask but use paper tape on both sides of the nose piece to completely eliminate fogging my glasses. It works! And it also eliminates two big gaps where air can go in and out. I see folks with surgical masks that have big gaps on both sides of the nose, and suspect that wearing a cloth mask with those gaps closed may be better than a surgical mask with lots of air leakage around the edges.
    When I feel I'm going to be more exposed, I put a surgical mask over my cloth mask, but that makes breathing a bit harder.

  4. iamr4man

    Not sure how this is counted. My sister, her husband, her son his family all wear kn95 masks. All (except the 4 year old) got Covid while unmasked. This is because my nephew’s 4 year old daughter got Covid at her pre-school. Before becoming symptomatic she spread it to all of them. Just a matter of dumb luck that my 95 year old mom didn’t get it.
    So how does that get counted? I’ll bet this has happened to a lot of people with the schools open.

    1. damgo2

      The study just asked people "do you always wear a mask indoors in public?" So that would have been counted as getting covid in the KN95 bucket.

      As mentioned earlier, it's really not measuring mask effectiveness, but the effectiveness of "people who regularly wear masks" at avoiding Covid.

  5. mistermeyer

    This survey leaves out an entire category of masks: 3-layer. i.e. cloth with filter. Enro, one example, lists test results (from an independent lab) that are on par with N95. AFAIK, there are a number of vendors selling similar 3-layer masks, so I'm surprised the CDC didn't include this category.

    3. fredtopeka

      Aaron Collins tests a bunch of types of masks and found Enro blocked about 70% of aerosols compared to 98 or 99% for N95s and KF94s.

      He tests the Enro here (a bit over 30 minutes in):
      https://youtu.be/dR2O98tKsQA

      He also has a link to a google doc with all the data he has gotten from his tests.

    4. coral

      My family & I have used Happy Masks, which are cloth with filter and very comfortable. For very risky situations (long airplane trips), we're using 3M N95. They're not very comfortable, but really protective and enable us to do things we'd otherwise avoid. With close family we go unmasked, but everyone is very careful and for gatherings at holidays everyone does rapid tests.

      We have avoided most indoor restaurants. Those we went to were after boosting and before omicron surge.

      What I find irritating is the mixed messaging and contradictory information that people who aren't careful about their news sourcing are getting. I think Biden administration has done best possible with the reality of America's current political divisions and the right-wing intentional disinformation campaign.

      I have never felt so pessimistic about this country. If I were younger I would move to Canada or Western Europe.

  6. Jimm

    https://www.sciencedaily.com/releases/2021/06/210623130716.htm (American Chemical Society)

    "With each fabric layer, the droplet-blocking capability improved by more than 20-fold. Interestingly, all of the three-layer cloth combinations the researchers tested were more effective than a three-layer surgical mask. The best masks for blocking droplets contained a hydrophilic inner layer of cotton or linen, an absorbent middle layer of a cotton/polyester blend and a hydrophobic outer layer of polyester or nylon. Machine washing the masks didn't decrease their performance; in fact, masks containing cotton or polyester worked slightly better after washing because of pore shrinkage."

    https://pubs.acs.org/doi/abs/10.1021/acsbiomaterials.1c00368

    1. KenSchulz

      Thanks for the link. My last round of homemade 3-layer cloth masks used polyester between cotton to (I hoped) generate an electrostatic charge for better capture of aerosolized particles as well as droplets. Also, I was using stronger nose clips than any of the commercial masks we’ve bought to date. Next batch will add foam weatherstrip on the clip. I wear eyeglasses, and now live in Minnesota, where fogging is a problem a large part of the year.

  7. Convert52

    Hmm, I expect this is a comparison of relative rather than absolute risk. So, say the odds of getting covid is 10% without a mask and 5% with, the chart would show a 50% reduction. I think a lot of people would be unimpressed be the difference if presented in absolute terms.

    1. golack

      True. And that's why it's always been a defense in depth,

      But you'll have to translate that reduced risk on an individual level to overall reduced transmission of Covid--this improvements in hospital case load and death rates.

      1. Convert52

        Note that the 56% reduction for cloth masks is marked as not being statistically significant. Bottom-line, the indicates that cloth masks may have a benefit, but nothing can be concluded from this study. Since there's no established standard for the quality of "cloth masks", it's not surprising that the data is noisy. Cloth mask could mean everything from fishnet to multi-layer highly effective masks.

        1. KenSchulz

          Exactly. ‘Cloth’ is an extremely broad category of materials. The ACS study that jimm cited is much better than most in characterizing the materials tested.

    1. DonRolph

      You mean omicron is not killing about 2000 people a day?

      Covid-19 now appears to be the third leading cause of death in the US.

      Some collapse.

      1. Spadesofgrey

        You realize, not for much longer means. 2500?? Nope. Nostril rip and detachment would serve you well. Matter of fact, deaths appear crested and have begun to fall. Oh, those reporting lags.

            1. DonRolph

              It appears that covid-19 is the third largest cause of death for most age groups:

              - https://www.cdc.gov/mmwr/volumes/70/wr/mm7014e1.htm

              Now we do not have such a detailed breakout of causes of death by age for 2020, but its we look at the 2019 numbers:

              - https://wisqars.cdc.gov/cgi-bin/broker.exe

              it would appear hat:

              - for ages 15 - 24 covid-19 is the 6th leading cause of death

              - for ages 25 - 34 covid-19 is the 6th leading cause of death

              - for ages 35 - 44 covid-19 is the 5th leading cause of death

              - for ages 45 - 54 covid-19 is the 4th largest cause of death

              - for ages 55 64 cvid-19 is the 3rd leading cause of death

              And since a significant portion of covid-19 deaths can be mitigated with vaccines, masks, and social distancing controls, covid-19 for all ages is a needlessly high cause of death.

              And minimizing it just continues this stream of death which covid-19 deniers have been driving since early 2020.

  9. cephalopod

    I have been surprised that I haven't caught covid yet, but maybe I shouldn't be. I wear a well-fitting KN95 all the time in public, and am vaxxed and boosted.

    I spent all fall interacting with unvaxxed kids at school, church, and scouts. Once vaccines became available for kids, a lot of the kids I know got vaccinated. So for all of Omicron I think that nearly half of the kids I interact with are vaccinated. The kids all wear masks (some better than others), and I am very careful about wearing mine. Even so, it's hundreds of people every week, and many of them are not vaccinated.

    Dozens of kids and adults at school have gotten covid, but not me. I spent the first half of January fully expecting to be taken down with a breakthrough infection that never happened. I suppose there is a chance that I had a very short infection that sneaked in between PCR tests, but I certainly haven't had any indication that I've been infectious to others.

    It will be exciting in May, when I'll be tested in my research study again and know whether or not I did manage to avoid infection.

  11. Justin

    Sure Some masks are better, but then few are willing to wear one at all now.

    Masks are like the economic aid provided. We should have tolerated more deaths and more hardship. Now we have inflation and way too many poor people survived the pandemic.

    “We had an economy where income was running short by $50 billion a month because of the pandemic, and we injected $150 billion to $200 billion a month into that economy. It’s perhaps not surprising that that’s led to an overflow of demand, which has generated inflation…”

    “… at least some economic slowdown will be necessary if inflation is going to be contained.”

    We need to fire some people so they can’t buy so much junk. Good grief.

    https://news.harvard.edu/gazette/story/2022/02/pandemic-only-partly-to-blame-for-record-inflation-says-lawrence-summers/

  13. tinfoil

    Is it worth pointing out the the differences between mask-type were not statistically significant? I don't think the authors even attempt a comparison, but you can see it in the fully-overlapping confidence intervals (For those not familiar with odds ratios: 1.0 mean no effect, 0.0 means full protection relative to unmasked people, so lower is better):

    K/N95: 0.17; 95% CI = 0.05–0.64
    Surgical: 0.34; 95% CI = 0.13–0.90
    "Cloth": 0.44; 95% CI = 0.17–1.17

    Now the combined odds ratio for wearing any mask was 0.44 (95%CI: 0.24-0.82), which might make you think that everyone was wearing cloth masks. But in fact around half wore surgical masks (and almost none wore N95), so my interpretation is that the "mask-type" ratios are overly optimistic, and there's little if any difference between surgical and cloth mask, perhaps for reasons people here already mentioned.

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