Mask or no mask? COVID Myths Busted!

Why should most people wear masks?
Wearing a mask decreases the number of people infected by an infectious mask wearer (“source control”), because it reduces by around 99% the number of droplets that are ejected during speech. It also probably somewhat decreases the likelihood of an uninfected wearer getting infected, although it’s less effective for this, since many of the droplets quickly evaporate into small droplet nuclei that are hard to block. Reducing the number of people infected has an exponential impact, because it decreases the effective reproduction rate, R.
About half of infections are from people that aren’t showing symptoms – so people that don’t know they’re sick are infecting others. Because masks are far more effective at blocking infection at the source, that means we need everyone to wear a mask in public, since otherwise unmasked people put those around them at risk.
Shouldn’t only sick people wear masks?
Patients without symptoms pose a risk of infecting others, so it’s not enough to wait until you have symptoms to wear a mask. Four recent studies show that nearly half of patients are infected by people who do not themselves have symptoms—thus they aren’t even coughing or sneezing yet, but they can spread the disease just by talking in close proximity to someone else.
Shouldn’t we just follow WHO’s guidelines?
WHO says “if you are healthy, you only need to wear a mask if you are taking care of a person with COVID-19”. WHO also says that “Studies of influenza, influenza-like illness, and human coronaviruses provide evidence that the use of a medical mask can prevent the spread of infectious droplets from an infected person to someone else and potential contamination of the environment by these droplets.” 
Remember, you don’t know if you’re healthy, and you don’t know if the people that you’re with are healthy either. So to follow WHO’s guidelines, you really need to be wearing a mask when around others.
Many countries have been clear about this. The U.S. CDC (Center for Disease Control) recommends wearing cloth face coverings in public settings” because “a significant portion of individuals with coronavirus lack symptoms” and they can be contagious spreaders of the virus. 
Other countries that are officially recommending mask use include China, Japan, France, India, South Korea, Canada, Germany, Brazil, Spain, Indonesia, Israel, the Czech Republic, Singapore, South Africa, Slovenia, Bulgaria, Slovakia, Austria, Bosnia, Mongolia, Taiwan, Colombia, Philippines, Ukraine, Uzbekistan, Vietnam, Cuba, Turkey, Chile, Zambia, Rwanda, Luxembourg, Panama, Malaysia, Poland, Ecuador, Singapore, Morocco, Kenya, Venezuela, Rwanda, Nigeria, Ethiopia, Guinea, Honduras, Hong Kong, Bulgaria, Benin, Cyprus.
Many countries have gone further, and mandated mask use in most public settings, including Indonesia, Israel, the Czech Republic, Slovenia, Bulgaria, Slovakia, Austria, Bosnia, Mongolia, Taiwan, Singapore, Colombia, Poland, Panama, Philippines, Uzbekistan, Ukraine, Vietnam, Cuba, Morocco, Turkey, Kenya, Zambia, Luxembourg, Ecuador, Chile, Venezuela, Honduras, Ethiopia, Rwanda, Benin, Guinea, Parts of China, and Parts of USA (including New York, New Jersey, Maryland, Pennsylvania, Connecticut, Puerto Rico, Los Angeles, Miami, Washington DC, San Antonio, Most of Hawaii, and San Francisco).
If it’s spread through the air, can a cloth mask really stop it? Isn’t the virus too small?
Coronavirus particles are so small that they can fit through the weave of most household cloth materials. Medical masks, such as N95 respirators, use special materials that create difficult to navigate pathways in the fabric that make it very hard for these tiny particles to get through the material. They also are specially fitted to the face of each healthcare worker to minimize gaps that these particles can get through.
Many commentators have been distracted by this, not realizing that the droplets that are ejected from an infected mask wearer are far bigger than the virus particles, and are easily blocked with around 99% efficacy, as shown in this recent NEJM paper that used laser light scattering to explore the effect. 
We don’t know for sure yet whether droplets ejected during breathing are also an important transmission path. These droplets are much smaller, and have a lower total viral load, compared to droplets from speech, but I haven’t found any studies that directly study the impact of this on COVID-19 transmission.
The good news, however, is that we do have a study that shows the impact of wearing an unfitted mask on seasonal coronavirus transmission, based on the amount of virus particles found in droplets ejected during breathing. In this study, the unfitted mask was 100% effective in blocking these for seasonal coronavirus.
There’s even a study that tested the efficacy of a cloth mask at blocking COVID-19. Unfortunately, there are some problems with the study:
  • Symptomatic people should stay home, so testing speech would have been more helpful than testing coughs
  • The test was done at 8 inches, which is much closer than people should be if following physical distancing guidelines
  • Only 4 patients were tested
  • The data analysis was not done correctly.
We can’t fix the first three problems, but we can fix the fourth. When we do, we find that over 95% of the viral load was blocked by the cloth masks.

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