Thread by @jonlevyBU

1. In the coming weeks, you will be in a room with someone with #COVID19. But that doesn’t mean you will get infected. The dose makes the poison, so your goal is to reduce your dose as much as possible.

How do you do that? TL;DR - #BetterMasks, ventilation, and filtration 🧵

2. First the basics - Watanabe et al. 2010 published a dose-response model for SARS-CoV, which has been used as the conceptual foundation for SARS-CoV-2 risk modeling. You want to get yourself as far to the left as possible.

3. The question is, how much dose reduction is possible using simpler measures under your control?

Important to remember that measures are cumulative and multiplicative. So stack a few up and you can make a big difference.

4. First, how much can #BetterMasks help? There are countless KF94/KN95/N95 that get filtration above 99%. 99% would reduce your dose by a factor of 100. If everyone had an equivalent mask on, that’s a factor of 10,000. Pretty good start, I’d say…

armbrustusa.com/pages/mask-tes…

5. But let’s be conservative and say that masking gives you a 90% reduction in dose, or a factor of 10.

(Parenthetically, remember how the math works. 50% reduction is factor of 2. 99% is factor of 100. So 99% is 50 times better than 50%).

6. You can also use ventilation to reduce concentrations. Even if you don’t have fancy technology, opening windows can make a big difference. Maybe a factor of 3-5 reduction.

nature.com/articles/75002…

7. Then there are portable HEPA filters. Performance varies, but you can easily get a 50% reduction in concentrations. More is certainly attainable.

cdc.gov/mmwr/volumes/7…

8. So with good ventilation, filtration, and masking, it’s easy to get a factor of 100 reduction in dose. And with universal use of #BetterMasks plus robust ventilation and filtration, we could be talking a factor of 10,000 or 100,000. I like those odds.

9. You can do much more detailed calculations at safeairspaces.com/safeairspaces-…, which is based on an excellent peer-reviewed article by @HoomanParhizkar @Wymelenberg @CorsIAQ and @ProfCharlesHaas.

10. Just as a simple example, their default settings lead to 9 of 21 people being infected. Masks at 50% efficacy + doubled outdoor air supply + modest filtration turns that into 1 infected. #BetterMasks and more aggressive ventilation and filtration turns it into 0.

11. So we don’t need a defeatist attitude, where we say we will all get exposed so why do anything. Our goal right now should be to reduce concentrations in all indoor spaces and to reduce inhaled dose for anyone in those spaces. We have the technology to do this.

12. Addendum - most of the above is individually focused. But a pandemic is collective. If we all do this, or more helpfully, put policies in place to allow all to do this, exponential growth quickly becomes exponential decline. And this protects all of us…