1/ My current estimates on modes of transmission & mitigation measures

From work on this & talking to a lot of scientists, my thinking is evolving. I thought it'd be useful to present my updated estimates, w/ hope of generating debate, finding new info to further polish this

2/ I have talked to many scientists, who have their own estimates, but prefer to not make them public. My estimates are not an outlier, many ppl are in same ballpark, not everyone of course

Trans. varies w/ setting, preventive meas. Attempt at avg for non or low-symptomatics

3/ These are the things that we know need to avoid, which I later relate to my estimates:

- Indoors
- Crowded
- Low ventilation
- Long duration
- No masks
- Talking / shouting / singing
- Close proximity

4/ My estimate for non/low- symptom. “talking” trans.

~75% aerosols: 1/2 (37%) at close proximity, 1/2 (37%) at room-level, 1% long range

~20% surfaces / fomite / direct contact btw people

~5% ballistic droplets, mostly accidental sneezing and cough. (generate aerosols too)

5/ These correspond with the amount of available evidence. Aerosols have a ton of evidence, and are the explanation for close proximity transmission for non-symptomatic people. Fomites have some evidence, but are not major (HT @CathNoakes in particular).

6/ Droplets have no evidence I am aware of. They are mostly “medical folklore”, most likely a century-old mis-interpretation of what’s really going in the close proximity situation for respiratory diseases (see https://www.sciencedirect.com/science/article/abs/pii/S0360132320302183)

7/ Droplets are for sure more important for transmission from symptomatic people who are coughing

8/ I have started a list of evidence for and against the different routes at: https://docs.google.com/presentation/d/11rY9tQtkFaV_M4N-hf5qp1_Xtuw8JYb4Qvv5e7BEmcc/edit#slide=id.p Please comment on things that should be added and removed, and provide references. The idea is that this can be an evolving “Wiki” document as we learn more

9/ Now let’s examine the things to **avoid** and what modes of transmission they eliminate, assuming my estimates are approx correct:

- Close proximity: this is directly one of the modes
- Outdoors: no room-level & long range, less close proximity (wind, UV), less fomites (UV)

10/ Not Crowded + long duration: reduced close proximity, room-level, fomites, and droplets
- Low ventilation: reduced room-level and long range
- No masks: reduced close proximity, room-level, long-range, fomites, and droplets

11/ - Talking / shouting / singing: reduced close proximity, room-level, long range, droplets (also less generation of fomites)

12/ So that’s my take. When all is said and done and we know the answer a lot better, I'd be extremely surprised if this doesn't look like a good guess based on what we knew at the time.

13/ I realize others have strong opinions in various directions. Let’s debate them, give the reasons and evidence why these % are wrong, give your estimates, and let’s think through this together.