Sorry for the long wait for a new update, I’ve been helping put together a new COVID lab, and I’ve been working long days for the past week. Today, I’ll give the update, then talk about a new study concerning masks.
Update: New confirmed cases continue to go down for the US, California and San Diego County. For California, the numbers are kind of flat. The reporting system in California was broken for much of last week, but the state says it’s working again. Death rates are coming down from their second peak. Comparing the new daily case numbers and the new death numbers make it clear that the virus has become much more survivable than it was in March and April.
New study on droplet transmission from various masks: A study was pre-published a few weeks ago that studied droplet transmission from various popular masks (Fischer EP, et al., Low-cost measurement of facemask efficacy for filtering expelled droplets during speech, Science Advances, pre-released August 7, 2020). The study used a system in which a speaker wearing a mask would say a prescribed phrase several times into a box through which a laser was shining. A camera would then capture droplets that were illuminated by the laser. The study used a relative scale for mapping mask benefit, with the N95 getting a relative score of 0, and no mask at all getting a score of 1. See the results in the photos.
Surgical masks did the second best after the N-95, and a 2 ply cotton mask with a sheet of polypropylene (like blue Shop Towel) fabric did third. I’m particularly happy to see the cotton and poly mask do so well, because that’s what I use! Performing poorly are knitted masks, bandanas, and especially the neck gaiter, which actually did worse than nothing! The authors speculate that this is because the fleece material may break up larger droplets into smaller ones instead of stopping them.
Shout out to my sister-law Penny who has made hundreds of masks in her home. The 2 ply cotton masks she makes have a pocket for inserting a filter or piece of poly like I use, and these masks did very well in this study! For extra credit, say the phrase “masks she makes” ten times fast.
I have never been a fan of the surgical mask because of the large side spaces that allow air to pass easily into and out of the mask from the side. I was surprised to see these masks do so well in this study. The answer may be in the experimental design, which captured droplets coming from the front of the mask, but excluded ones from the side. I would like to see a study that captures that too! This just shows that experimental design matters, and just because a study shows something, doesn’t mean the study was designed to detect all relevant things!
Mask wearing has become controversial, but the data supports the idea that masks reduce viral transmission, and that lower viral load on exposure leads to better medical outcomes!
Don’t fear, but be smart,