Thread by @DrEricDing

BREAKING—CDC urges either **double-masking** or use **surgical mask with tight fit** to better protect against threat of new and more contagious variants of the coronavirus. Two methods substantially boost fit & protection, says CDC report. #COVID19 🧵 washingtonpost.com/health/2021/02…

2) “We know that universal masking works,” said John T. Brooks, medical officer for CDC’s covid-19 response. “And now these variants are circulating … whatever we can do to improve the fit of a mask to make it work better, the faster we can end this pandemic.”

3) “One is wearing a cloth mask over a surgical mask. The second is improving the fit of a single surgical mask by knotting the ear loops and tucking in the sides close to the face to prevent air from leaking out around the edges and to form a closer fit.”

4) Both of those methods reduced exposure to potentially infectious aerosols by more than 95 percent in a laboratory experiment using dummies, the report said.

5) A three-ply surgical mask blocked 42 percent of particles from a simulated cough, and a three-ply cloth mask blocked 44 percent. But a cloth mask covering a medical mask blocked 92 percent of the particles, the report said.

6) In a second experiment, a dummy wearing double masks and one wearing a knotted/tucked medical reduced exposure for an unmasked dummy by 82 percent and 62 percent respectively....

7) When one dummy was not wearing any masks and the one acting as the bystander wore a double mask or a knotted/tucked medical mask, the bystander’s exposure was reduced by 83 and 64.5 percent respectively...

8) ...But when both dummies wore double masks or knotted/tucked medical masks, the bystander’s exposure was reduced by more than 95 percent in both situations!!

9) @linseymarr offered these tips for ensuring the best mask fit:
“You should not be able to see or feel any kind of open spots around the edges of your mask, especially around your nose, which is why a metal bridge is so important for fitting tightly around the nose.

10) “You don’t want gaps around the cheek or chin. One way you can check when you are breathing, does it feel like air is leaking out of the side? Put your hand on the edge to see if you feel anything. When you breathe in, you should feel suction up against your face.”

11) Other signs of leakage include eyeglasses fogging up or cold breath coming from the sides of masks while outside. Another test involves breathing hard in front of a mirror to see if you blink while wearing a mask, which would indicate leakage from the top of the mask.

12) “If masks fail these tests, Marr said, you should try a different kind of mask. “Peoples’ faces have such different shapes that you can try to find something that can work better for your face,” she advised.

13) Key is to avoid the critical side gap in the mask! cdc.gov/mmwr/volumes/7…

14) INTERESTING DETAIL—While both people wearing masks is best (green circle), if only one person out of 2 wears a mask, the double mask (of surgical plus cloth) seems superior to single surgical that is knotted & tucked.

All else equal—do both. But if just do one, DOUBLE MASK.

15) VIDEO—I think the knotted & tucked surgical mask is tricky for people to understand without a full video. Here is the video to demonstrate how to do it.


(HT @Arriadna)

16) Here is @CDCDirector @RWalensky explaining the new double masking / tight surgical mask guidance today.

17) Getting lots of N95 / KN95 mask questions — assuming you have one, and it’s a real one (not a knock off, @projectn95 can advise), the key thing is again FIT. I’ve seen many KN95 that have bad fit. Nose bridge should be tight. Use straps if available. Ear loops stretch tight.

18) ⚠️ONE-PARTY MASKING UNEQUAL:

➡️If only one person is masked, is it better if the source (exhaling person) is masked, or if the air receiver (inhaler) is masked for someone inhaling risk?

💡CDC study: **Source-masking** (red) is much better for minimizing exposure!

19) I’m shocked that the CDC report didn’t emphasize this! This is a serious problem in areas with many unmasked!!

⚠️In fact, it almost looks like there is little to no difference if the source of the exhaled air is not masked vs neither masked (yellow circle!). Damn—Not good.

20) Luckily, it looks like if you follow the new CDC guidance on either double masking or the enhanced surgical mask fit, then it matters less if the source of the 3rd party air is not masked. You are still protected!!

21) Here is the best demonstration video of how to tie the new surgical mask properly.

https://twitter.com/drericding/status/1359563442819112960

22) Another surgical mask folding demonstration, from wonderful folks at @GMA.

24) This is also why I advised to people to switch to premium masks that has enhanced filtration. Just make sure snug fit. See 🧵 for details.

https://twitter.com/drericding/status/1353186978519539712?s=21

https://twitter.com/drericding/status/1353186978519539712

25) We need people to understand that 1 sloppily-worn mask is not enough. And mask wearing by the source of a virus is critical, and hence why double masking is key.

https://twitter.com/drericding/status/1359840583435624457

26) 💡 I want to reemphasize this figure from the recent CDC study—

📌 everyone masking clearly more effective than 1 person masking.

📌 And if only 1 person, double masking better than poor unfitted surgical mask.

📌A poorly worn single mask by receiver has little protection