re: Ben Swann Highlights Latest CDC study that shows masks don't work to prevent flu viruses

quote:

---

The science ain't settled. But I have a hunch masks can drop the infection rate at least a few percent

---

In highly controlled settings, masks have shown to be fairly effective, particularly in these two hospital based studies. N95 unquestionably reduced transmission (~25% the number of transmissions to healthcare workers wearing them all the time). Surgical masks had a confidence interval barely crossing 1, so I would bet that they probably help to a lesser extent than no mask at all (I believe the infection rate was ~75% vs no mask but did not re-review the numbers...I think the low end of the CI for risk was around 0.67 and up to something in the 1.03ish area). Those familiar with statistics can point out that there's a chance, then, that they actually increase the risk. Those more familiar would argue that is very, very unlikely, with more subjects we would know better, and stating that they "probably reduced some transmission" is a fair statement.


But there's a meta analysis out there from sometime between '09 and 17 that I read as well. It had something like 17ish trials, most were community based. There were 2 trials that showed evidence that a mask slowed transmission:
1) influenza positive volunteers coughed into a petri dish and virus was cultured in 9/9. Then they coughed through an n95 and a surgical mask held 20cm away. No virus was cultured in either of these settings. This is a group of 9 people. It didn't account for any clinical outcome or leakage around a mask. So it does sort of "prove" that the mask is a capable filter, but it doesn't by any stretch of the imagination show that wearing one is going to reduce the risk of spread to those around you, because there has not been, to my knowledge, any measure of what percentage of breath is actually filtered through a surgical mask on the "hard science" side, and there have been plenty of trials with clinical outcomes (for one, see above). The other positive data in the collection of trials included cloth masks during the Spanish Flu pandemic. I believe it showed reduced transmission in field hospitals in Boston, but I also think it included handwashing and the unmeasurable variable of open air. It is a trial that is over 100 years old and makes it difficult to really assess what was being measured because times/tech were so different, it was done outside, and there are an abundance of trials that show no significant difference. It is, however, an outlier worth mentioning.

The last positive one in favor of masks that I recall in the bunch was something like this:
A small cohort inside of a house with a positive initial influenza case who wore masks AND handwashed within 24h of symptoms reduced ILI transmission to other household contacts. The rest of the study showed essentially no difference.


My take home from the above:
N95 work fairly well. They don't zero the rate, but they work as good as anything out there that I've seen.
Surgical masks probably beat nothing if I'm wearing them, because I know how to properly wear one and am comfortable enough not to fidget in it all day
Based on the data in about 14 distinct trials, when a large group of nonmedical personel are asked to wear a mask in a community setting, it alone seems to have no difference in the rate of transmission on respiratory viral transmission, particularly influenza and the common influenza like illnesses that are seasonally transmitted.



ETA: I can find the referenced 2nd meta analysis if anyone is actually interested. There are many more out there now. I'd caution anyone reading anything published in 2020 to very critically read and attempt to find any admitted or subtle bias, because most of what I've read seems poorly designed, underpowered, and has high risk of bias. I've admittedly not read much on the matter for about 2-3 weeks after reviewing the above and reaching the above conclusions.