[M T]

I asked for a pointer to a study that measures whether masks help or not.  As there are different national CDC-type organizations that have different advice on masks, I find it strange that some people seem adamant on one side or the other.   

So I googled and found an article asking the same question.  Here are 3 studies the article mentioned. (NOTE: There may be other studies that contradict these.  I am not able to do a medical literature search.  If you find conflicting studies, or identify problems in these studies, please contribute.)

Study 1: 

...However, compliance with mask use was less than 50%. In an adjusted analysis of compliant subjects, masks as a group had protective efficacy in excess of 80% against clinical influenza-like illness. The efficacy against proven viral infection and between P2 masks (57%) and surgical masks (33%) was non-significant. ... In compliant users, masks were highly efficacious.

Study 2:  This study paired hand hygiene with wearing masks versus neither, so it doesn't really indicate anything about face masks themselves.

Study 3: Subjects in residence halls at a university

Participants were assigned to face mask and hand hygiene, face mask only, or control group during the study. Discrete-time survival models using generalized estimating equations to estimate intervention effects on ILI and confirmed influenza A/B infection over a 6-week study period were examined. A significant reduction in the rate of ILI was observed in weeks 3 through 6 of the study, with a maximum reduction of 75% during the final study week (rate ratio [RR] = 0.25, [95% CI, 0.07 to 0.87]). Both intervention groups compared to the control showed cumulative reductions in rates of influenza over the study period, although results did not reach statistical significance.

If I read their numbers correctly, it appears that the face-mask-only group appeared to do well in the first week, but did less well each succeeding week, getting to the same level as the control group by the final week.  The face-mask-hand-hygiene group's numbers got better each week.  (Presumably these changes were not statistically relevant in this study, but might be interesting if someone were to test for that.  Tiring of compliance?  False sense of protection?)

Unfortunately none of these test hand-hygiene vs hand-hygiene + face mask.

I certainly hope that no hoarders are preventing health-care workers from being able to get masks.  But no one should be chastised if they use a mask to protect themselves.

The WHO & CDC have been seeing this disease progressing for two months.  I would have hoped that was enough time for the word to get out to hospitals and other health care professionals to stock up on all their supplies, including masks.   (That's not to say those professionals should be out-of-luck if they didn't stock up.)

[M T]

I asked for a pointer to a study that measures whether masks help or not.  As there are different national CDC-type organizations that have different advice on masks, I find it strange that some people seem adamant on one side or the other.   

So I googled and found an article asking the same question.  Here are 3 studies the article mentioned. (NOTE: There may be other studies that contradict these.  I am not able to do a medical literature search.  If you find conflicting studies, or identify problems in these studies, please contribute.)

Study 1: 

...However, compliance with mask use was less than 50%. In an adjusted analysis of compliant subjects, masks as a group had protective efficacy in excess of 80% against clinical influenza-like illness. The efficacy against proven viral infection and between P2 masks (57%) and surgical masks (33%) was non-significant. ... In compliant users, masks were highly efficacious.

Study 2:  This study paired hand hygiene with wearing masks versus neither, so it doesn't really indicate anything about face masks themselves.

Study 3: Subjects in residence halls at a university

Participants were assigned to face mask and hand hygiene, face mask only, or control group during the study. Discrete-time survival models using generalized estimating equations to estimate intervention effects on ILI and confirmed influenza A/B infection over a 6-week study period were examined. A significant reduction in the rate of ILI was observed in weeks 3 through 6 of the study, with a maximum reduction of 75% during the final study week (rate ratio [RR] = 0.25, [95% CI, 0.07 to 0.87]). Both intervention groups compared to the control showed cumulative reductions in rates of influenza over the study period, although results did not reach statistical significance.

If I read their numbers correctly, it appears that the face-mask-only group appeared to do well in the first week, but did less well each succeeding week, getting to the same level as the control group by the final week.  The face-mask-hand-hygiene group's numbers got better each week.  (Presumably these changes were not statistically relevant in this study, but might be interesting if someone were to test for that.  Tiring of compliance?  False sense of protection?)

Unfortunately none of these test hand-hygiene vs hand-hygiene + face mask.

I certainly hope that no hoarders are preventing health-care workers from being able to get masks.  But no one should be chastised if they use a mask to protect themselves.

The WHO & CDC have been seeing this disease progressing for two months.  I would have hoped that was enough time for the word to get out to hospitals and other health care professionals to stock up on all their supplies, including masks.   (That's not to say those professionals should be out-of-luck if they didn't stock up.)