Studies Showing Masks Prevent Virus Transmission

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    There is considerable evidence that masks do, in fact, reduce the transmission of viruses, including COVID, and thus can save lives if used widely. Here are several studies supporting this (two of which are based on analyzing all the available prior studies).

    “Efficacy of face mask in preventing respiratory virus transmission: A systematic review and meta-analysis,” Travel Medicine and Infectious Disease (2020)
    —A total of 21 studies met our inclusion criteria. Meta-analyses suggest that mask use provided a significant protective effect (OR = 0.35 and 95% CI = 0.24–0.51)…This study adds additional evidence of the enhanced protective value of masks, we stress that the use masks serve as an adjunctive method regarding the COVID-19 outbreak…The effectiveness of masks has been proven in different settings, populations, and areas.

    “Community Use Of Face Masks And COVID-19: Evidence From A Natural Experiment Of State Mandates In The US,” Health Affairs (2020)
    —This study provides evidence from a natural experiment on the effects of state government mandates for face mask use in public issued by fifteen states plus Washington, D.C., between April 8 and May 15, 2020. The research design is an event study examining changes in the daily county-level COVID-19 growth rates between March 31 and May 22, 2020. Mandating face mask use in public is associated with a decline in the daily COVID-19 growth rate by 0.9, 1.1, 1.4, 1.7, and 2.0 percentage points in 1–5, 6–10, 11–15, 16–20, and 21 or more days after state face mask orders were signed, respectively. Estimates suggest that as a result of the implementation of these
    mandates, more than 200,000 COVID-19 cases were averted by May 22,

    “The role of community-wide wearing of face mask for control of coronavirus disease 2019 (COVID-19) epidemic due to SARS-CoV-2,” Journal of Infection (2020)
    —We assessed the effect of community-wide mask usage to control coronavirus disease 2019 (COVID-19) in Hong Kong Special Administrative Region (HKSAR)… The COVID-19 incidence in HKSAR (129.0 per million population) was significantly lower (p<0.001) than that of Spain (2983.2), Italy (2250.8), Germany (1241.5), France (1151.6), U.S. (1102.8), U.K. (831.5), Singapore (259.8), and South Korea (200.5). The compliance of face mask usage by HKSAR general public was 96.6% (range: 95.7% to 97.2%). We observed 11 COVID-19 clusters in recreational ‘mask-off’ settings compared to only 3 in workplace ‘mask-on’ settings (p = 0.036 by Chi square test of goodness-of-fit)…Community-wide mask wearing may contribute to the control of COVID-19 by reducing the amount of emission of infected saliva and respiratory droplets from individuals with subclinical or mild COVID-19.

    “Face Masks Against COVID-19: An Evidence Review,” (Preprint).
    —Here, we synthesize the relevant literature to inform multiple areas: 1) transmission characteristics of COVID-19, 2) filtering characteristics and efficacy of masks, 3) estimated population impacts of widespread community mask use, and 4) sociological considerations for policies concerning mask-wearing…The preponderance of evidence indicates that mask wearing reduces the transmissibility per contact by reducing transmission of infected droplets in both laboratory and clinical contexts. Public mask wearing is most effective at stopping spread of the virus when compliance is high.

    I recommend people read these studies, and others on the efficacy of masks, before claiming that “masks don’t work” based on something you heard online or in a Whatsapp group.


    There’s a much simpler way to put it:

    If someone has COVID-19 and wears a mask, it’s very unlikely they will spread it.

    Even if you’re feeling fine, or you had an anti-bodies test, or you caught COVID-19 in the past, you should still wear a mask. There’s no telling when you may catch it and be contagious and a simple piece of cloth goes a long way to prevent other people from getting sick.


    The data discussed shows that masks reduce the change of becoming infected with Covid19, though as with any such virus, it probably won’t prevent you from becoming infected if you are exposed to it. Only a vaccine would do that, Fortunately, for most people, becoming infected with Covid19 rarely makes you sick. If you feel that avoid Covid19 is a life or death matter (e.g. an 85 year old with a dysfunctional immune system and lung diseases), rather than relying a mask lowering the probability of becoming infected, you should isolate yourself in sealed environment which would probably prevent catching the virus.

    An analogy would be walking out into a battlefield with or without a kevlar vest. The bulletproof vest will certainly reduce your chance of being killed, but it won’t prevent it (e.g. many soldiers in spite of wearing them). To avoid being shot, it is best to avoid going to a battlefield.


    @akuperma To extend your battlefield moshol, if everyone wears a mask it would be like jamming all the soldiers’s guns.


    akuperma. If yo get infected, you have considerable chance to be a cause of someone dying down the chain coming from you. Currently at about 80%. How do you feel about this?


    The מלאך המות doesn’t check for masks.

    Note to moderator: I’m in Israel.


    Masks are incredibly harmful because they lower oxygen levels in the blood (leading to hypoxia) while raising carbon dioxide levels (leading to hypercapnia), and force you to inhale and exhale more forcefully, stressing the cardio-pulmonary system. This is especially dangerous for the elderly.

    Even doctors who wear surgical masks do so to prevent them from drooling into a patient’s wound, not to protect them from pathogens, and hospitals are required to increase oxygen levels to compensate for the loss of oxygen in the mask. There’s an entire body of OSHA regulations that requires that workers be tested to see if they’re fit to wear a mask and for how long—it’s dangerous stuff and can cause dizziness, fainting, and headaches.


    “Masks are incredibly harmful because they lower oxygen levels in the blood (leading to hypoxia) while raising carbon dioxide levels (leading to hypercapnia), and force you to inhale and exhale more forcefully, stressing the cardio-pulmonary system.”

    Absolutely false for most people. I have asthma and have measured my own oxygen saturation with an FDA approved pulse oximeter while wearing a mask. In fact I did it again just before writing this comment, My oxygen saturation is consistently 97% to 98% whether I wear a mask or not.

    Stop promoting this dangerous disinformation.


    ““Efficacy of face mask in preventing respiratory virus transmission: A systematic review and meta-analysis,” Travel Medicine and Infectious Disease (2020)”

    Only one of the 21 studies looked at COVID-19; the other 20 studies were for other respiratory viruses. In that one case control study, N95 masks reduced COVID-19 transmission by 97% in healthcare workers.


    What’s more dangerous than to dismiss mask wearing os to overstate the effectiveness of wearing masks in protecting against Covid. Although there are many studies that seam to suggest that mask wearimg may be somewhat effective, it is very difficult to properly conduct a controlled study in a real world environment. We also have to keep in mind that mask wearing has become a political issue, and any study questioning the eefects of masking would likely not see the light of day. There os a shul in my community that requires mask wearing as all the shuls in my community do, that had a very large outbreak. I cannot help but think about all the high risk individuals that attended that shul armed with the quote from the CDC director “Masking is more effective than a vaccine”. Then there is this tidbit buried on the CDC’s website.

    “Neither surgical mask can effectively remove submicrometer sized aerosol particles such as aerosolized bloodborne pathogens”


    Dip, you are right.
    Shuls should also increase ventilation – keep windows open, have Merv-13 and higher filters, and high-risk individuals should stay home. Still, any reduced transmission likely reduces spread and severity of the illness in the case of outbreak.


    MasKup-FALSE! There is no such thing as a “Mask Test” What you’re probably referring to is the N95 Fit Test which is done to determine the proper size for the wearer. The Fit Test doesn’t measure O2 levels! It’s done to make sure the mask is fully sealed and cannot let any air in! Stop with the false info. There is no such thing as a Mask Test and regular surgical masks don’t cause breathing problems. I have asthma and have been wearing a mask for years in the clinical setting without any difficulties.


    It used to be true that surgical masks protect the patient and not the care providers, but this has changed a lot in the last 20-25 years, with sars, mers, avian flu, pig flu, Ebola etc. However, since those epidemics had low numbers in the West, new industrial standards for surgical masks were not adopted in USA and EU.Yet, since most masks are produced in Asia, they meet those quality standards.


    If it prevented the disease, than no one wearing a mask would ever get Covid19. The statistics say only that wearing a mask reduces the chance of getting sick from Covid19, from perhaps one chance in fifty (the chance of an infected person becoming ill) down to something less. Other statistics show that most infected people were wearing masks.


    not “high risk” i.e. elderly people or those with condition should stay away, but careless people should stay home.


    akuperma what are you trying to prove? People who correctly wear respiratory protection do not get sick despite working with the deadliest pathogens. It’s true that users should be trained, and for N95 they should also be fit-tested, but I can’t solve myself all the problems in the world. I have helped people for free (I suppose a stupid idea) but most people are simply uninterested, and I can’t help that. There are lots of people who wear a mask either as a political statement, or because they think having it on the chin and occasionally pulling it up is better than nothing. Well, it is better than nothing, but just barely. Wearing a mask correctly makes a lot of difference.


    >> wearing a mask reduces the chance of getting sick from Covid19,
    Reducing chance of transmission in one person has dramatic increase on transmission over time. With say 5 day transmission, just 10% decrease in one person, will reduce transmission by 50% in one month.


    akuperma >>Other statistics show that most infected people were wearing masks.

    If most people wear masks, then most infected people would wear masks. Possibly from interaction with people not wearing mask.

    To get an idea whether being careful works , look at plots of Rt transmission. Rt shows how many people one person infects. If Rt is less than 1, then pandemic is dying out. If it is higher than 1, it increases.

    Rt was _4_ in NY state on March 1. This is what happens when nobody takes precautions. It fell to 1 on March 25, when shelter started, went down to 0.7 (significant decrease) until end of May when reopening started, and went back to 0.9-1.1 range until now. So, you can see the possible range is between 0.7 and 4.

    Right now, Rt in NY State is at 0.99 (maybe even 0.9999999?!). So, you can see that Rt can be above (increasing pandemic) or below 1 (decreasing) just maybe on your actions below. This illustrates the Rambam that says that one should imagine himself as tipping the scales of the world.

    in March-April


    It seems like some of our posters are obsessed with denial of any mainstream medical and public health guidance on what measure have been shown to have material benefits in viral transmission and lowering of infection rates. No one is saying that masks or social distancing eliminate risk or are 100 percent effective but until we have proven vaccines and therapeutics, they are better than injecting chlorine or using any of the other unproven remedies being pushed by right-wing zealots.

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