Tolerating the Pandemic #4: The Ventilation Edition
This is #4 in the series of how we can tolerate the pandemic in a lot of slow, steady progress and hard work. As a quick recap, the first post laid out a bit of a roadmap (March 23, 2020); the second (April 17, 2020) and third (June 26, 2020) noted updates on the categories described in the first.
In the two months since my previous post, one of the most exciting advances has been in improved understanding of the transmission dynamics of SARS-CoV-2, particularly with respect to aerosol-like transmission. An Aug 11 New York Times article has a good summary of some of the research in this area. Tl;dr: Ballistic (large droplet) transmission is probably still a big factor, and is helped quite a bit by masks. Aerosol transmission is a big contributor particularly to superspreader events (and particularly indoors). Cloth or surgical masks help but are not a silver bullet, particularly in crowded, confined spaces.
Why is this exciting? Because it helps us bring more tools to bear against transmission. It furthers the (already very strong) case for the outdoors being substantially safer than being indoors; it reinforces the importance of masks as part of a source control strategy; and it suggests that improvements to ventilation and good (HEPA or MERV-13 or higher) filtration also have a role to play in reducing the number of people who get infected from a transmitting individual.
For more on this, I suggest starting with the Harvard Healthy Buildings report from June and this slide deck from CU Boulder. As a taste of some of the great things in there, this slide, analyzing the infection probability of a known real super-spreader event (an indoor choir practice) while changing different components of the scenario, such as increasing ventilation. Or just moving the darn thing outside, which would have approximately solved the problem. (The advantage of being outside was already clear as of the previous update in June, but more evidence and understanding of why is good.)
With that said, let's get back to the framework from the previous posts: Testing, PPE/Supplies, Treatments, and Societal changes to reduce contact. I'll fold ventilation improvements into the latter, since that's where I'd previously discussed things like plexiglass barriers in retail.
So that's .. not what I'd like to see, but we have to be careful reading that. In update #3 (June), we were at 450k tests/day. As of now the US is up to about 700k. Better than June, but case counts are also still higher than they were in June; test positive rates are only just now getting back down to where they were. The good news is that we're testing a lot; the bad news is that with cases so high our testing isn't anywhere near sufficient to keep cases low.
N95 mask production continues to ramp up about as expected. 3M says it's on track to produce 95 million per month by October in the US, and 2B annually for the global market. In our previous update, 3m was trying to hit 50M/month by July, which they seem to have. Recall that DHS estimates we need about 300M masks/month in the US, but 3M isn't the only supplier. We're basically on track ramping up our PPE capacity, but it also still may be until the end of 2020 that we've really gotten this solved.
Anecdotally, N95 masks are showing up occasionally on Amazon now (before getting re-restricted for healthcare use only). Reusable options are emerging. But there are still few high-quality surgical masks (ASTM level 1-3 certified) available for the general public, which would be an improvement over the high variance in quality of uncertified masks.
The Purell Indicator
- There are candidates based upon several different technologies.
- Results appear promising that infection yields protection for at least several months for most people.