The Science of Masks 6: Reviews of Randomized Controlled Trials
Time to talk about "scientific consensus."
Dharma gets a bus!
Sorry, I’m getting ahead of myself - maybe I should start at the beginning. This is Part 6 of explaining what anyone with two working brain cells would have known, had they read the published literature on face masks and the spread of infectious disease.
While engaged in this important work, I also have a 90s sitcom called Dharma & Greg on autoplay and we’re already up to Episode 14, in which the couple have agreed to buy another car. Dharma has gone to an auction and come back with a used school bus (a 1968 Bluebird).
The Bluebird “comfortably seats 24 adult or 38 sixth graders.” That’s more than the entire useful staff at the CDC, with the added bonus that the sixth graders just learned algebra so some of their math will be correct.
This post, and probably the remaining few as well, should be much shorter than the previous couple. So let’s fire up the Bluebird’s 9-liter engine and power on through this thing. “It’s like driving an ice cream truck except we don’t sell drugs.”
Scientific consensus? When do those people ever agree on anything?
The phrase “scientific consensus” has become a shorthand way of saying “I’m right and smart people agree with me.” You see, years ago super smart college students found out they could win arguments by saying:
“actually, scientific studies have shown…”
but then other, more super smarter college students learned to counter that with:
“those studies have been debunked”
“Debunked” being a newer magical term that means “I’m right and you’re wrong.” This is an ongoing part of the long standing human tradition of masking ignorance with appeals to authority.
The new killer comeback is the phrase “scientific consensus.” I’m not sure where I can get the phone number for this very important Office of the Consensus of Science but they are clearly the real deal since everyone refers to them.
Of course you and I never seem able to contact this office. Instead we are told to rely on the media, who are just like the Catholic church in the middle ages. The real truth is only available in Latin and you don’t speak the Latin (you peasant), so a trusted authority (CNN, The New York Times, Fisherman’s Weekly) must translate.
But the reality is that we can look at the literature for ourselves and decide what things are generally accepted as true, and which are controversial.
Literature reviews of randomized controlled trials of masks
One resource in the scientific literature is something called a literature review. These are summaries drawn up by people familiar with a field of study, to summarize what they find when they look into published studies. There are several of these summaries of randomized controlled trials of masks. Let’s do something craaazy and read them.
1. Disposable surgical face masks for preventing surgical wound infection in clean surgery (Vincent & Edwards 20161)
Surgical masks are a well known and recognized piece of PPE worn by healthcare professionals, but there is surprisingly little evidence they reduce infections. This review was published by the Cochrane Library, which is an organization in the UK that publishes detailed reviews on different subjects to inform healthcare decision making.
The review covers the use of surgical masks, and whether they actually reduce the chance of infection of the patient. In the words of the authors the purpose of the review was:
To determine whether the wearing of disposable surgical face masks by the surgical team during clean surgery reduces postoperative surgical wound infection.
The authors looked at 250 citations and fully examined 97 papers. Three studies are included in their analysis, and the authors begin by pointing out there is not much research on the effectiveness of surgical masks (and this was in 2016).
Given the widespread use of surgical face masks, research into this topic remains surprisingly neglected.
Gee, ya think? So we have state governors issuing ridiculous but also wide-reaching mask mandates based on an area of research that is “surprisingly neglected?” Gavin Newsom has done more research on hair gel than the State of California has done on masks.
The authors clearly make the point that laboratory studies showing masks filter particles or pathogens do not prove those masks will have an impact on rates of infection.
Much of current national and international policy is based upon equivocal evidence from laboratory studies of the filtration efficiency of surgical face masks and of potential contamination of the surgical field using settle plates. Such indirect evidence is of questionable clinical relevance.
Their conclusion: it’s not really possible (based on the available evidence) to determine if surgical masks actually reduce infection.
All three studies showed that wearing a face mask during surgery neither increases nor decreases the number of wound infections occurring after surgery. We conclude that there is no clear evidence that wearing disposable face masks affects the likelihood of wound infections developing after surgery.
[In more interesting news: Greg and Dharma are randomly driving around San Francisco in the bus, picking up people and taking them wherever they’re headed. This is probably more productive than what I’m doing right now. They just picked up a whole kid’s soccer team whose bus had broken down. Back in the 90s you could do things like that. By “things like that” I mean have an actual life where you did actual things without being harassed by loons for the act of breathing.]
2. Face masks to prevent transmission of influenza virus: a systematic review. (Cowling et al. 20102)
Many of the studies on the effectiveness of masks look at the transmission of influenza, and there are several literature reviews of these studies. Published by Cambridge University Press in the journal Epidemiology and Infection, this paper looked at six studies in healthcare settings and four in community settings.
Our review highlights the limited evidence base supporting the efficacy or effectiveness of face masks to reduce influenza virus transmission.
As has been noted many times before, the laboratory results do not translate into reduced infections in actual use.
While there is some experimental evidence that masks should be able to reduce infectiousness under controlled conditions, there is less evidence on whether this translates to effectiveness in natural settings. There is little evidence to support the effectiveness of face masks to reduce the risk of infection.
See, it’s not just us. People who get paid to read things like this also find little reason to think masking you and your toddler will do any good. Strip Junior naked and have him roll in the mud for a while - it’s actually good for him.
3. Effectiveness of N95 respirators versus surgical masks against influenza: A systematic review and meta-analysis (Long et al. 20203)
One issue with surgical masks is the open sides where aerosols can escape, in contrast to the typical N95 mask. Surgical masks are sometimes compared against N95 respirators to see if the N95, which fits more tightly and filters smaller particles, is more effective than the surgical mask. Published in the Journal of Evidence Based Medicine, this paper reviewed six RCTs comparing the two mask types.
Previous meta-analyses concluded that there was insufficient evidence to determine the effect of N95 respirators. We aimed to assess the effectiveness of N95 respirators versus surgical masks for prevention of influenza by collecting randomized controlled trials (RCTs).
A total of six RCTs involving 9,171 participants were included.
The authors conclude there is not sufficient evidence to recommend use of N95 respirators by anyone not in close contact with patients.
The use of N95 respirators compared with surgical masks is not associated with a lower risk of laboratory-confirmed influenza. It suggests that N95 respirators should not be recommended for general public and non high-risk medical staff those are not in close contact with influenza patients or suspected patients.
So everything we have seen here has been consistent with what we learned in the last post when we looked directly at the RCTs ourselves. See, we’re not idiots!
[Show update: Dharma and Greg have taken the bus to a modern art exhibit but because of the torrential rain, water has filled one of the exhibits (Inverted Cone #8) and this is flooding the parking lot and endangering the building. Old Yeller comes to the rescue and Dharma drives everyone to safety.]
A non-stupid summary of the literature (Fisherman’s Weekly is welcome to quote me on this):
Okay, here is the best, most concise summary of the literature that I can come up with:
Although there is mechanistic evidence (such as laboratory experiments with dummies) for the effectiveness of masks, randomized controlled trials of mask use in community settings have consistently failed to demonstrate a benefit.
The use of personal protective equipment, including masks, when used by trained healthcare workers who are caring for known infectious patients, sometimes has benefit.
Next time …
Part 7 will be another short one. We’ll be looking at what the World Health Organization had to say on this subject in 2019, right before everyone starting acting like cattle. Here’s a preview - they say the exact same thing (although they use more words to do it).
We’ll also be watching D&G Episode 17: “The Official Dharma & Greg Episode of the 1998 Winter Olympics” in which they mock the crass commercialism of the Olympics.
Vincent M, Edwards P. Disposable surgical face masks for preventing surgical wound infection in clean surgery. Cochrane Database Syst Rev. 2016;4(4):CD002929. Published 2016 Apr 26. doi:10.1002/14651858.CD002929.pub3
https://pubmed.ncbi.nlm.nih.gov/27115326/
Cowling BJ, Zhou Y, Ip DK, Leung GM, Aiello AE. Face masks to prevent transmission of influenza virus: a systematic review. Epidemiol Infect. 2010;138(4):449-456. doi:10.1017/S0950268809991658
https://pubmed.ncbi.nlm.nih.gov/20092668/
Long Y, Hu T, Liu L, et al. Effectiveness of N95 respirators versus surgical masks against influenza: A systematic review and meta-analysis. J Evid Based Med. 2020;13(2):93-101. doi:10.1111/jebm.12381
https://pubmed.ncbi.nlm.nih.gov/32167245/