1) If anybody comes across posts saying that the CDC says masks don’t work, here’s a fact-check you can use

Basic fact-check:
https://www.politifact.com/.../no-cdc-who-study-does-not.../

The paper: https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article

2) Summary-
CDC published the paper but didn't conduct the study

The paper DOES NOT talk about SARS-Cov-2/COVID-19. This meta-analysis looks at existing research data about transmission of *INFLUENZA*

3) The authors conclude that the set of papers reviewed (studying the effects of handwashing, covering your face when you sneeze or cough, sanitizing objects and surfaces, and/or mask-wearing) did not find significant reduction of *INFLUENZA* transmission. That’s ALL they claim

4) These are important quotes from the paper:

“Most studies were underpowered because of limited sample size, and some studies also reported suboptimal adherence in the face mask group.”

5) “...respirators, such as N95 and P2 masks, work best when they are fit-tested, and these masks will be in limited supply during the next pandemic. These specialist devices should be reserved for use in healthcare settings or in special subpopulations..."

6) “In lower-income settings, it is more likely that reusable cloth masks will be used......There are still few uncertainties in the practice of face mask use, such as who should wear the mask and how long it should be used for."

7) "In theory, transmission should be reduced the most if both infected members and other contacts wear masks, but compliance in uninfected close contacts could be a problem (12,34)."

8) "Proper use of face masks is essential because improper use might increase the risk for transmission (39). Thus, education on the proper use and disposal of used face masks, including hand hygiene, is also needed.”

9) “...as with hand hygiene, face masks might be able to reduce the transmission of other infections and therefore have value in an influenza pandemic when healthcare resources are stretched.”

10) Personal Notes:

A single Literature Review doesn't and can't imply a scientific consensus on any topic. This thread is meant to demonstrate how crucial context is, both in how we read sources of information and how we decide what to do with that information

11) Cherry-picking the statement that the studies reviewed didn't find significant reduction in *INFLUENZA* transmission, and saying it means that masks are useless to stop SARS-Cov-2 transmission, is incorrect and irresponsible. Read the quote above about "improper use" of masks

12) And then after you read this thread, read the paper! The writing is easy to digest, and some of their study populations (like Australians performing Hajj) are really interesting!