Will Vaccine + Mask Control Delta? A Modest Proposal for N95 Masking

Have a look at (CNN) White House frustrated with Irresponsible Delta Variant Coverage…Napkin Calculation #4. I’ll drop in some text.

So let’s try another intervention, vaccine+masks. (PNAS) Face masks considerably reduce COVID-19 cases in Germany. Quoting,

…Weighing various estimates, we conclude that 20 d after becoming mandatory face masks have reduced the number of new infections by around 45%.

This approximates a relative risk reduction of 1/2 = 0.5.  In combination with 100% vaccination,

      • For Pfizer and Delta, R_mask = 9*( 0.2 to 0.4)*0.5 = 0.9 to 1.8.

This is a bad number. If napkin calculations have credibility, it implies disaster. Though not fact,  it should not be dismissed. It is the result of high viral load of Delta breakthroughs.

The implication  is that R remains above 1, implying runaway, forest fire growth. This glum observation is based on the typical public-use mask, which is derived from the fluid barrier procedure mask, which is not designed for infectious disease control. This class of masks is relatively comfortable to wear; it reduces transmission by about half. In the above calc, it’s the factor 0.5.

Healthcare workers in infectious disease wards use far more effective and uncomfortable N95 masks, which are designed to protect against most aerosols. Experimental factors for transmission reduction may not exist; let’s guess 0.1, a tenth.

So substitute 0.1 for 0.5:

  • For Pfizer and Delta, R_mask = 9*( 0.2 to 0.4)*0.1 = 0.18  to 0.36

Less than 1, these are good numbers! If everyone in the U.S. wore N95 masks and practiced perfect aseptic  technique, COVID would vanish. Given the political climate,  unreasoning resistance to masks, and general impracticality, why have I written this?

Many people might be eager to make limited use of N95 masks, in situations they perceive as hazardous. Mask receptivity may jump in those who meet Delta up close and personal. So this is a proposal for the White House task force:

  • Subsidize N95 production.
  • Make the masks widely available.
  • Possibly be surprised at the uptake.

As for refusniks, you do what you can; they do what they will. They may soon become more receptive.



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