Thread by @jljcolorado

1/ Several implications of this mask study:

- N95 well-fit should protect 99%.

The lower 83% in the real world likely in part due to LEAKS and POOR FIT

Shows room for improvement of fit (N95 w/ straps behind head better than ear loop ones like KN95). Make sure tight to face

https://twitter.com/linseymarr/status/1489687309201158145

2/ Also likely impact of fake KN95 that don't filter well.

Don't buy KN95 on Amazon, full of fakes. Buy from reputable safety suppliers

Korean KF94 better, few fakes

[Of course there could also be a few % of transmission thru eyes or other minor pathways + "experiment noise"]

3/ IMPORTANT that the reports are the 1-way protection in same indoor environments.

If everyone wears similar masks, the we get (approx.) the effect SQUARED

17% of virus escape infected (100-83). And 17% of virus in air is inhaled. So prob. Of infection 0.17^2 = 3% vs. no mask

4/ So comparison if EVERYONE:

- No mask: 100%
- Cloth mask: (1-.56)^2 = 19%
- Surgical: (1-.66)^2 = 12%
- N95 / KN95: 3%

Same math as this @PNASNews study:
pnas.org/content/118/49…

5/ Let's state the results another way:

Compared with everyone wearing N95 / KN95, the probability of infection is:

- 4 times larger if all surgical
- Over 6 times longer if all cloth
- Over 35 times higher if all unmasked

Huge effects

6/ To state it another way for the "my freedom" crowd:

- If we all wore N95/KN95, we could spent 4 times longer in indoor activities than if all surgical

- 6 times longer than if all cloth

- 35 times longer than unmasked

[For the same risk]

So GOOD MASKS GIVE US FREEDOM!

7/ Now, these results are with lots of fake KN95 out there, and with very poor @CDCgov communication about the importance of N95 and mask fit

We should be able to do better & improve the results substantially, if govts. provide good quality N95 (not KN95) and explain fit better

8/ Also important: spread of virus is EXPONENTIAL.

Those transmission reductions are in 1 GENERATION of infection (every ~4 days)

Like compound interest, they accumulate exponentially

Imagine if the bank told you they are going to increase your loan interest RATE x4 or more!

9/ Good point that the remaining transmission w/ N95 may not all be leaks and fakes, but also some transmission at home w/o masks

Numbers are noisy, and there are confounders in both directions

But trend is very clear and consistent w/ real mask tests.

https://twitter.com/michael_hoerger/status/1490050532786020360?t=4it7F9Ym7hWVt5Vf64h4dw&s=19

10/ Although note that people who wear N95 / KN95 are less likely to bring the virus home, and thus less likely to infect people there.