Post #792: Mask use and asymptomatic cases

I just stumbled across this article (or, same thing, here) and thought it was well worth repeating.  If for no other reason that a) it’s about COVID-19, b) it’s incredibly logical and fact-based, and c) it explains something fairly important.

The gist of this is that:

  1. When you are exposed to COVID-19, the amount of COVID-19 that you breathe in is a strong determinant of how sick you’ll get.  The higher the initial dose, all things equal, the sicker you’ll get.  The lower the dose, the less sick.
  2. Masks greatly reduce the amount of virus you inhale, when you are exposed.
  3. The least sick you can get is an “asymptomatic case”, that is, a person who was infected but fought back the virus without having any symptoms.
  4. A high rate of mask use greatly increases the fraction of infections that are asymptomatic infections.

The first point is well documented in scholarly literature and by experiment, for viral infections in general, and for COVID-19.  The second point has been documented by direct testing of masks/respirators.  The third point is a definition.  The fourth point relies on a few cases studies of cruise ship/meat packing plants were early mandatory universal mask use was implemented.

For a subject where so little of it seems to make sense, I thought this was outstandingly straightforward and well-documented.  Something like 40% of current coronavirus cases are now thought to be asymptomatic.  That’s substantially higher than estimates early in the pandemic, where asymptomatic cases were thought to be relatively rare.  Plausibly, it’s not that the early estimate was wrong, is that high rates of mask use are creating a larger fraction of asymptomatic infections.

More speculatively, if the above is true, can’t we extrapolate to the full spectrum of disease severity?  One thing I noted about the Chinese experience is that their mortality case rate (deaths per known infection) fell substantially over time.  I assumed that’s because they got better at treating cases.  Now I’m wondering of the average severity of illness declines over time because the mask use rate goes up.  And whether the low current US case mortality rate isn’t just due to the shift in mean age of the infected (toward younger persons), but may also be due to a downward shift in mean severity of cases as a high fraction of the population used masks.