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Mask wearing protects the wearer and others from SARS-COV-2: CDC finally publishes recommendations.

SARS-COV-2 EM photo courtesy NIAID

On November 10, the Centers for Disease Control (CDC) published a recommendation for public to wear cloth masks, both for protection of the wearer and for other people in proximity to the wearer. This publication is detailed and contains references to multiple observational studies and investigations that show masks are at least moderately effective.

My only question is: why did it take so long to publish this advice? Masks have been advised by experts or mandated by politicians since last spring. The delay could only be due to political opposition.

The evidence in the publication is mostly from several months ago. There are new preprints, however, including this one from MedRxiv that was first published October 7 and was revised as of November 11:

We used a cough aerosol simulator with a pliable skin headform to propel small aerosol particles (0 to 7 µm) into different face coverings.  An N95 respirator blocked 99% of the cough aerosol, a medical grade procedure mask blocked 59%, a 3-ply cotton cloth face mask blocked 51%, and a polyester neck gaiter blocked 47% as a single layer and 60% when folded into a double layer. In contrast, the face shield blocked 2% of the cough aerosol. Our results suggest that face masks and neck gaiters are preferable to face shields as source control devices for cough aerosols.

Clearly, an N95 respirator is preferable for very small particles but a medical grade procedure mask is also better than nothing; face shields are completely inadequate. Larger particles (greater than 7 microns in size) are more readily blocked.

With the daily count of new cases in the US exceeding 150,000 this week, now is definitely the time for everyone to start wearing masks in public. Now is also the time to prohibit public dining and drinking (these being the highest-risk public activities found.)

The most likely source of new infections at this time (assuming the public doesn’t go out) is intrafamily transmission. Thus, the word has gone out to people to not gather in person for Thanksgiving or Christmas. I don’t think it will help– less than half of all family gatherings will be stopped.

The only thing that will stop the novel coronavirus now is rapid immunization of everyone. Unfortunately, widespread shots will not begin until next spring, so we are in for a very bad winter.

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