Thread by @smartrestartaps

1/ Airborne transmission, and the 3 feet vs. 6 feet question: A 🧵 with links for policy advocates trying to sort through the science...

WARNING: Nuance Ahead

2/ COVID-19 is mainly spread by inhaling small particles.

Timeline with illustrations, articles, studies:
#COVIDisAirborne #masks4All #bewareOfSharedAir #ventilation. See: its-airborne.org/covid19-timeli… via @AerosolizedC19

Airborne Transmission FAQ by experts: tinyurl.com/FAQ-aerosols

3/ In addition, here's Dr. @linseymarr and Dr. @jljcolorado's bibliography regarding "Transmission of COVID-19." They're top experts.
tinyurl.com/p4h9mbzz

"What We Know" 2021 summary: Respiratory plumes/short-range "close" exposure are <1.5 m (4.92 ft)
tinyurl.com/3sbktpzz

4/ RESEARCH: A review of 172 studies from 6/20 in The Lancet found distance of 1 m (3.28 ft) reduces infection risk; 2 m (6.56 ft) is better.



Risks of COVID-19 transmission: 82% less at 1 meter apart, then cut in half for each extra meter
tinyurl.com/4xdaydhc

5/ In same Lancet report, face masks estimated to reduce transmission — pooling results — by about 85%, but better masks (N95s) produced best results (96% reduction); cloth masks (such as students have) were estimated to reduce risks by 67%. (FYI: Eye protection: 78% less risk)

6/ RESEARCH: An analysis on "rebreathed" air found when distancing of 2 m (6.6 ft) is maintained, then TIME spent confined indoors with others, not proximity, dominates exposure risks from aerosol particles.

Close contact <2 m = much more risk
 
tinyurl.com/58hnfxn8

7/ RESEARCH: Mayo Clinic calculated risks with distance and masks.

Masks were KEY; but watch video (leakage!)

Without masks, risk was 17% at 3 feet, and 3% at 6 feet.

"CDC guidance is good - 6 foot has an important impact on the number of particles."

tinyurl.com/439cmj5p

8/ Dr. @nausheenrshah also shared calculations on risk:

Probability:
📌 Scales inversely with VENTILATION; Increasing 3 ACH (air refreshes/hour) ➡️ 6 ACH halves risk.
📌 Linear with TIME; Longer ➡️ more risk.
📌 Reduce DISTANCE to 3 ft ➡️ Risk goes up 4x

https://twitter.com/nausheenrshah/status/1366252525066866689?s=20

9/ RESEARCH: A review of school districts in MA and 3 ft vs. 6 ft standards found: Lower physical distancing policies can be adopted in school settings with masking mandates without negatively impacting student or staff safety.

https://twitter.com/EricTopol/status/1371266606727237635?s=20

10/ Study has critics. Some questioned flaws such a 3 ft district, with 20% attendance, may have 8 ft space. (It's policy, not reality, in data.)

tinyurl.com/4vdfj3v8
tinyurl.com/tvzr438z

Others say 3 ft. OK w/ 💯 mask compliance + ventilation.
tinyurl.com/5meek7da

11/ More critiques: Confidence interval was so big that 6 ft could actually have reduced cases by as much as 47%.

Others questioned if 3 ft would be a good idea with more transmissible/more severe variants now spreading.

We wrote a 🧵 on variants:

https://twitter.com/smartrestartaps/status/1368617167931990018

12/ COMMUNITY SPREAD: For us in @ArlingtonVA, more people in a room = more probability that someone will bring an asymptomatic case of COVID-19.

The risk for a class of 15 is 6%.
But for a class of 25, it's 10%.
For one day x 4-6 classes. (No cohorting)
covid19risk.biosci.gatech.edu

13/ The Event Risk Assessment tool assumes 3x undercount. Local data indicates our testing for kids may catch as few as 1 of 17 cases. Asymptomatic "silent transmission" between kids could play a much bigger role than we know in this pandemic.

https://twitter.com/smartrestartaps/status/1372592386627530752?s=20

14/ This thread and article are a good summary of different perspectives on the CDC's changes.

https://twitter.com/HuffmanLabDU/status/1372309665887911936

nytimes.com/2021/03/16/hea…

15/ In VA, 3 ft has always been OK, but APS chose to go half capacity and use 6 ft rule this year.

>30% of APS rooms are below code: lack fresh air for full occupancy. Problem!

@BarbaraKanninen @Monique4APS @PriddyAPS @ReidForSchools @cdiaztorres240 @SuptDuran @BrianStockton19

16/ If APS were to utilize 3 ft distancing, even JUST for little kids, then APS should INCREASE and STRENGTHEN other mitigations, @APSVaSchoolBd.

Here are some ways we can strengthen the plan and support keeping our schools open...

https://twitter.com/smartrestartaps/status/1354518152596623365?s=20

17/ CDC has minimum 6 ft distance for eating indoors, but has recommended closing cafeterias.

Eating indoors right now is too risky — at any distance.

Let's go outside and take COVID-19 off the menu.
Make it happen for ALL kids, APS.

smartrestartaps.org/vital-issues/l…

18/ APS is being reckless with older kids who are not cohorting as CDC recommended. There's no time for rooms to clear air between classes.

FYI: HEPA air cleaners adding 5.5-5.7 air changes of clean air would clear air and reduce inhalation risks by 6x!

tinyurl.com/ycpzbfre

19/ APS, you still have rooms that must get 2 HEPA cleaners to hit the goal of 5-6 ACH (air changes per hour) of CLEAN AIR.

Nearly 700 experts have endorsed this standard now:

https://twitter.com/WBahnfleth/status/1372922215507881992?s=20

Don't increase capacity without increasing clean air!

https://twitter.com/smartrestartaps/status/1366837251179745280?s=20

20/ Universal masking is vital. Let's provide better masks to students and teachers. Just a tiny leak (2% of the surface) can reduce a mask's filtration efficiency by almost 80%.

But better, fitted masks + ventilation (5 ACH goal) combine to reduce risk.

https://twitter.com/DavidLKeating/status/1346855545693761539?s=20

21/ Before any school schedule changes, we want APS to explain plans for C19 testing — for kids with/without symptoms.

Is APS ready to contact trace kids sitting within 6 ft? How? Is APS sending emails about possible exposures or confirmed diagnoses?

https://twitter.com/ambilinski/status/1353751984852131841

22/ OK, that's it! Please comment with any key studies on the 3 ft/6 ft question that you've found.

https://twitter.com/VVuorinenAalto/status/1341310299236954112

@threadreaderapp unroll

FYI: Source for leakage stat... h/t to @kprather88 for noting this study recently.

tandfonline.com/doi/full/10.10…

A second excellent link for mask data. We are huge advocates for masking, but masks are best when combined with other strategies. They aren't going to be 100% — especially as used by little kids and with different quality levels.

https://twitter.com/linseymarr/status/1370005674906812416?s=20

23/ ADDITION: Thoughtful perspective on school building reopenings, new variants, and the distance question by @dgurdasani1 and colleagues. Covers all the reasons for concern about relaxing in guidelines at this point in time.

ineteconomics.org/perspectives/b…

24/ ADDITION: Dr. Don Milton's take on what schools must do: tinyurl.com/4s5zruem

(Experts' expert on airborne disease)

📌 Increase clean air to 10L/s*person (makes 5.2 air refreshes/hour in avg. APS room)
📌 Contact tracing
📌 Outdoor lunch
📌 Better masks
📌 👋 washing