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The WHO on Facemasks and Pre-symptomatic Contagion

Published by marco on


The article Here’s what WHO says your mask should have to prevent COVID-19 spread by Beth Mole (Ars Technica) details the technical specifications for making your own facemask.

tl;dr: “you’re probably doing it wrong, guidance suggests.”

The WHO says:

  • “[…] masks should only ever be used as part of a comprehensive strategy in the fight against COVID.”
  • “WHO now recommends that healthy members of the public wear homemade or commercially-available fabric masks in places where the new coronavirus is circulating widely and where physical distancing (staying 6-feet apart, etc.) is not possible or is difficult.
  • “[…] a minimum of three layers is required for fabric masks”
  • “[…] these masks are for source control only, not personal protection—that is, they can help prevent the person wearing the mask from spreading the virus, but they will not necessarily protect the wearer from becoming infected.”
  • Masks are not a replacement for physical distancing, hand hygiene, and other public health measures,

Here in Switzerland, there is still no mask requirement almost anywhere in public. It is strongly recommended to wear them on public transportation, but the SBB reports that 90% of people aren’t wearing them. It is honestly a mystery to me how Switzerland ended up with the #1 ranking for combating COVID-19. The numbers speak for themselves, though—the spread is, for all intents and purposes, at a standstill.

Once I start commuting again, I will be wearing a mask. I wasn’t interested in being part of the first wave. My interest in being part of the second wave is similarly low.

Pre-symptomatic transmission

The article WHO butchers asymptomatic COVID comments. Here’s what they meant by Beth Mole (Ars Technica) takes the WHO to task for “butchering” their message, but honestly makes quite a mess of summarizing the WHO message nearly as badly.

Still, more than halfway through the article, she finally sums up the relevant terminology.

  • Symptomatic case = Someone who is infected and has symptoms at some point.
  • Asymptomatic case = Someone who is infected but never develops symptoms.
  • Pre-symptomatic = The phase of a symptomatic infection when a person may test positive for the virus and/or may spread the virus but has not yet developed symptoms.
  • Pre-symptomatic transmission = Spread of the virus from a symptomatic case during their pre-symptomatic phase.
  • Asymptomatic transmission = Spread of the virus from an infected person with no current symptoms. This transmission could be from a pre-symptomatic person or a truly asymptomatic case, depending on how the terms are being used.
“The WHO has consistently used asymptomatic transmission only when talking about truly asymptomatic cases.”

Where I think I disagree with the author is where she deems the WHO “confusing” when they have been consistent and others have constantly misinterpreted the terminology, using their own definitions. That’s honestly not the WHO’s fault. It may be their problem, but it’s not their fault.

There are a few points of interest:

  1. Many people mean pre-symptomatic when they say asymptomatic. Truly asymptomatic people are very rare with COVID-19, although their known prevalence may increase as more is known about the disease.
  2. As far as public safety is concerned, there is no need to distinguish between pre-symptomatic and asymptomatic transmission: both indicate individuals who can infect others without knowing that they have the disease. As far as contagion is concerned, it doesn’t matter whether they exhibit symptoms a week later.
  3. Judging by how well certain countries have this first wave of the pandemic under control (Switzerland is a good example), pre-symptomatic transmission doesn’t seem to be as large a problem as some seem to think. E.g. Fauci in the U.S. thinks 25%-45% of cases might be transmitted this way. If that were the case, it would be much harder to trace and squash COVID-19 to the degree that some countries have.

I’m cautiously optimistic that pre-symptomatic transmission is less of an issue than some think. It would mean that it’s possible to keep COVID-19 under control by tracing super-spreaders and squashing outbreaks quickly.

The U.S.‘s inability to squash its rate has less to do with pre-symptomatic transmission and more to do with an utter lack of planning, discipline, and organization. People in the U.S. don’t trust anyone or anything and they’re not particularly well-trained at doing anything for the common good, so their follow-through has been much less effective than in European countries.