A Head Full of Coronavirus Research, Part 45

We were blessed with a visit from the IB at the coronavirus briefing yesterday, and it ran long with some really incredible information and statements so there is a separate post on that, and it might include ranting, reader discretion advised.

Here is my big picture take for the day, which is subject to revision as the research continues to unfold.  The first wave in the spring was kind of terrifying, especially if you didn’t look closely at even the early data.  We didn’t know what the disease would be like, we weren’t really good at treating it yet, it came after the most vulnerable first and hardest.  That wave, however, receded pretty quickly, not because of lockdowns or anything else, but because the weather changed and enough people were infected to slow transmission in a less favorable environment for the virus.  Then the summer wave hit, and although there were fewer lockdown type reactions, the virus receded faster, with a lower toll.  Partly we were smarter about treatment, but it would be foolish to think the less severe lockdowns didn’t play a role, by allowing enough people to get infected to slow transmission more quickly.  And in that wave, I don’t think weather had much to do with the diminution of spread, it was all about the difficulty of the virus in finding enough uninfected targets.  Now we are at the third “wave”, which isn’t going to be as big as the others on a testing adjusted basis, or result in as much  severe illness.  And this wave, I believe, will also recede fairly quickly, partly because much of it is in lower population areas than in the earlier waves, and partly because some of the population was already infected.  So we have been through this a couple of times already this year and panic should be avoided, but it probably won’t be.

If I would like you to take one thing away from the recent research summaries it is this.  The infectious dose of CV-19 is very small, a few hundred particles.  If you are healthy, probably takes more for a serious infection.  If you are old and/or frail or unhealthy, might take less.  If the virus gets to your lungs, apparently one virion, or virus particle, is sufficient to infect a cell and begin replicating.  No reason to think the same think isn’t true of the cells in the upper respiratory airway.  So when you read the mask study summarized below, keep that in mind and now you understand why I say, they may stop transmission in some individual encounters with the virus, they do not stop it at the macro level, across hundreds, thousands of encounters.  And now matter what anyone else says, it is absolutely true, and not just an attempt to be funny, to refer to masks as virus and pathogen collection devices.  That is their whole purpose and that is what they do.  So there you are with a mask in front of your face accreting virus particles.  Yep, that definitely has no risk.  What could possibly go wrong?

This is actually a pretty useful mask study, done in Japan using mannequins, with real CV-19.  (Japan Mask Study)   This study was done by placing two mannequins in a chamber, fitting them with various types of masks and seeing what happens with exposure to CV-19.  Kind of similar to the study in Nature Medicine earlier this year.    Human respiration and coughing was simulated and the spread of resulting droplets and aerosols tracked.  One mannequin head breathed out a mixture including the virus.  The other one simulated breathing it in.  Viral loads dropped in a manner inversely proportional to distance but infectious virus was detected even 1 meter away.  Compared to no mask, at an average viral load a cotton mask reduced virus uptake by 20% to 40%.  An N95 mask had the highest blocking potential at 80% to 90% reduction.  But infectious virus penetration occurred even when an N95 mask was completely fitted to the face with adhesive tape.  When a mask was put on the expelling mannequin, cotton and surgical masks blocked about 50% of virus particles and an N95 mask, a much higher percent.  With a higher viral load, as you would expect, more virus got through, event the N95 mask showed only about 90% effectiveness.  At low viral loads, very little virus was transmitted, but this was also the case in an unmasked situation, in other words wearing a mask offered no additional protection.   The study did not include examining long-term use of a mask with repeated encounters and what may happen in regard to buildup on the mask.  The big picture takeaway to me is that masks are not at a population level going to stop transmission, they simply don’t prevent the possibility of infection over a large number of encounters.  And this study involved affixing a mask properly to a dummy head; in real life masks are regularly worn improperly and simply don’t fit well.

And one more item for now, also on masks.  The Annals of Internal Medicine publishes regular updates from a “living” review on mask research and recommendations.  (AIM Update)  This is exactly the kind of rigorous examination of research that a number of government bodies have conducted.  Everyone concludes that there isn’t evidence that shows masks actually slow community transmission.  This update finds no basis to change the previous recommendation of insufficient evidence for benefit.  Real science.