> I would have hoped that in our current age of misinformation, that sources people trusted would not actively lie, but there you go.
Find a meta-analysis of mask wearing to prevent infection that was published at the time. Or find some RCTs of mask wearing to prevent infection. There are lots of papers looking at infection control - it's an important part of healthcare. Have a look at how they describe the quality of evidence.
> Transmission of viruses was lower with physical distancing of 1 m or more, compared with a distance of less than 1 m (n=10 736, pooled adjusted odds ratio [aOR] 0·18, 95% CI 0·09 to 0·38; risk difference [RD] −10·2%, 95% CI −11·5 to −7·5; moderate certainty); protection was increased as distance was lengthened (change in relative risk [RR] 2·02 per m; pinteraction=0·041; moderate certainty).
Face masks only achieve "low certainty"
> Face mask use could result in a large reduction in risk of infection (n=2647; aOR 0·15, 95% CI 0·07 to 0·34, RD −14·3%, −15·9 to −10·7; low certainty), with stronger associations with N95 or similar respirators compared with disposable surgical masks or similar (eg, reusable 12–16-layer cotton masks; pinteraction=0·090; posterior probability >95%, low certainty). Eye protection also was associated with less infection (n=3713; aOR 0·22, 95% CI 0·12 to 0·39, RD −10·6%, 95% CI −12·5 to −7·7; low certainty). Unadjusted studies and subgroup and sensitivity analyses showed similar findings.
This is disingenuous. The study you cite has a large effect size with low certainty ("Face mask use could result in a large reduction in risk of infection"). Best available data was that they probably help a lot, but we don't know yet, based on data from COVID19.
At the time COVID19 broke out, we had a ton of data from flu viruses and masks. That data clearly showed masks reduced viral loads a lot.
Was it perfect data? No data is perfect, especially 3 months into a new infection. But when the anti-mask recommendations came out, they were lying.
Studies range in effect sizes, but all the ones I read in March 2020 showed significant reductions in flu infection rates with masks. There were nice studies on cloth versus surgical versus N95 at the time too (summary: surgical and N95 were similar in performance, and much better than cloth, when used without full hazmat).
We know a lot more, specific to COVID, today. But that was best available evidence in March.
If it was so well established that mask wearing's effectiveness has low certainty, then the following tweet from the US Surgeon General was definitely a lie:
"Seriously people – STOP BUYING MASKS! They are NOT effective in preventing general public from catching #Coronavirus, but if healthcare providers can’t get them to care for sick patients, it puts them and our communities at risk!"
Effectiveness doesn't just mean "can this mask trap particles?" -- because it's clear that FFP3 masks can do this. Effectiveness also means "In a particular situation with a thousand people, how many if them will be infected if none of them wear a mask, vs if all of them wear a mask?"
Healthcare professionals have to shave facial hair; they use good quality masks that are tested for conformity; they have sessions where their masks are fitted for them; they have training about how to put on, take off, and wear the mask; they have support to help them put on PPE; and they use the mask as part of a bundle of PPE that includes gowns, gloves, hand-sanitising, and eye protection.
In a healthcare situation we see that this package of measures does reduce infection. (And then we struggle to understand what's doing what because it's all a big confounded mess)
But for the public, going about day to day activity, it was really hard to see that masks would do much good.
And it's hard to do that even today: people in this thread are saying that it's obvious cloth masks do nothing but p95s are super effective. No-one can post any good quality evidence for that. All we get a some pretty rough studies that are trying to disentangle a bunch of measures to see which had most effect.
* Cloth masks reduce viral loads by somewhere around 30-70%.
* High-quality masks reduce them by e.g. 70-95% depending on how they're fitted.
* We know risk of infection (and severity) is related to viral load, but we don't quite know how.
* We have a lot of well-documented evidence from Asia about reduced infections when high-quality masks are used consistently (e.g. buses in China, hospitals in Singapore, etc.).
* We know masks significantly reduce R0, but we don't know by how much; error bars are huge, and dependent on a slew of other variables.
The key difference between public health settings and hospital settings is opportunities to be infected. As a doctor, I might have 10 opportunities per day, and if I don't have properly-fitted PPE one of those times, and I'm susceptible, I'll catch COVID19. This means half-measures do very little.
In a public health setting, it's a numbers game:
* Personal: If I have 1 opportunity per 2 weeks to be infected, and I reduce odds by 50%, I'm half as likely to catch COVID personally.
* Public health: If I reduce infection odds by 50%, R0 is cut in half. That's huge. Our exponent is very different.
So cloth masks are definitely worth the $2, but won't stop you from catching COVID if you take other risks. If everyone wore N95 or even surgical or nanofiber masks, COVID would probably be gone pretty quickly.
Find a meta-analysis of mask wearing to prevent infection that was published at the time. Or find some RCTs of mask wearing to prevent infection. There are lots of papers looking at infection control - it's an important part of healthcare. Have a look at how they describe the quality of evidence.
Here's a well-known paper, published in a high impact reputable journal in June 2020. https://www.thelancet.com/journals/lancet/article/PIIS0140-6...
Distancing is rated at "moderate certainty"
> Transmission of viruses was lower with physical distancing of 1 m or more, compared with a distance of less than 1 m (n=10 736, pooled adjusted odds ratio [aOR] 0·18, 95% CI 0·09 to 0·38; risk difference [RD] −10·2%, 95% CI −11·5 to −7·5; moderate certainty); protection was increased as distance was lengthened (change in relative risk [RR] 2·02 per m; pinteraction=0·041; moderate certainty).
Face masks only achieve "low certainty"
> Face mask use could result in a large reduction in risk of infection (n=2647; aOR 0·15, 95% CI 0·07 to 0·34, RD −14·3%, −15·9 to −10·7; low certainty), with stronger associations with N95 or similar respirators compared with disposable surgical masks or similar (eg, reusable 12–16-layer cotton masks; pinteraction=0·090; posterior probability >95%, low certainty). Eye protection also was associated with less infection (n=3713; aOR 0·22, 95% CI 0·12 to 0·39, RD −10·6%, 95% CI −12·5 to −7·7; low certainty). Unadjusted studies and subgroup and sensitivity analyses showed similar findings.
These certainty ratings come from GRADE. https://bestpractice.bmj.com/info/toolkit/learn-ebm/what-is-...
Low certainty means "The true effect might be markedly different from the estimated effect".
This doesn't feel like lying. It feels like making the best of a bunch of not very good data.