Contrary to claims by anti-maskers, face masks do help reduce COVID spread

A review of 38 separate “studies” upon which anti-maskers falsely base their claim that “masks are useless”

covid-19_cultured_isolated_microscope
This scanning electron microscope image shows SARS-CoV-2 (yellow)—also known as 2019-nCoV, the virus that causes COVID-19—isolated from a patient in the U.S., emerging from the surface of cells (blue/pink) cultured in the lab. (Image credit: NIAID-RML)

[Updated 9/11/2021: Claims 1-9 are described below the summaries.]

Ever since the start of COVID, there has been a loud minority of people who claim that face masks don’t reduce the risk of COVID. Some anti-maskers claim that no masks are effective at protecting anyone while others claim that only N95 or better masks are effective. And both groups claim that the science supports their claims.

When confronted about these claims, most anti-vaxxers I’ve interacted with don’t bother to point to specific scientific studies on the subject, but a few do. And the single most common reference I’ve been sent is a link to an anti-abortion site, LifeSiteNews.com. The article claims to have 47 studies that show that masks are ineffective at protecting people from COVID.

I’ve reviewed all 47 links over the last few days and read all the referenced studies that I could get my hands on to assess whether or not the studies actually showed that “masks are useless.” What follows is a summary of my assessment of each of the studies, by reference number in the LifeSiteNews article. I will update this article with the details of how I reached my conclusions for each paper at a later date.

Summary of findings:

  • Of the 47 referenced “studies,” 9 are duplicates, leaving 38 total links.
  • Of the remaining 38 references, only four had results that supported the claim that masks were ineffective/useless.
  • 27 demonstrated that masks were effective (to various degrees of effectiveness) at filtering particles of the size of the SARS-CoV-2 virus and larger.
  • I couldn’t draw any conclusions on four of them due to not being able to locate a free version of the study online.
  • The last three were studies that were not applicable, opinion not backed up by data, and/or mathematical models.

The table below details the links by reference number and whether the study supports, rejects, et al that masks are ineffective/useless.

Claim Ref. # Conclusion Claim Ref. # Conclusion
1
Study does not support claim
25
Study does not support claim
2
Study does not support claim
26 Mathematical model, not a study. Misleading
3
Study supports claim
27
Study does not support claim
4
Study supports claim
28
Study does not support claim

(duplicate of #38)

5 Abstract does not support claim. Full study unavailable (duplicate of #32 & #41) 29
Study does not support claim

(duplicate of #39)

6
Study does not support claim
30 Contamination study; does not address mask effectiveness at all. Misleading (duplicate of #40)
7 Study unavailable – no conclusion 31
Study does not support claim
8
Study does not support claim
32 duplicate of #5 & #41
9
Study does not support claim
33
Study supports claim

(duplicate with #43)

10
Study does not support claim
34
Study supports claim
11
Study does not support claim
35
Study does not support claim

(duplicate with #44)

12 Study unavailable – no conclusion 36
Study does not support claim
13
Study does not support claim
37
News article does not support claim
14
Study does not support claim
38 duplicate of #28
15
Study does not support claim
39 duplicate of #29
16 Study unavailable – no conclusion 40 duplicate of #30
17
Blog, references do not support claim
41 duplicate of #5 & #32
18 Duplicate of #17 42
Study does not support claim
19
Study does not support claim
43 duplicate of #33
20 Letter on exercise effects of masking is not a study. Misleading 44 duplicate of #35
21
Study does not support claim
45 Abstract does not support claim. Full study unavailable
22
Study does not support claim
46
Study does not support claim

(duplicate of #47)

23 Study unavailable – no conclusion 47 Duplicate of #46
24
Study does not support claim

I also assessed each link for whether it was original research, a review of other studies, or “gray” literature (not new research but based on the research of others). This is what I found:

  • 25 of the links were original research
  • Four of the studies were “gray” literature and/or not applicable to the claim(the blog post, news article, opinion letter, and mathematical model).
  • None were reviews of research that attempted to combine multiple studies into a greater whole (systematic reviews and meta-analyses) or define the current state of knowledge on the subject of masks (scoping review). Many of 26 original research studies were referenced in these eight reviews.

The table below details the links by reference number and what type of study the links are.

Summary table for type of study (original research, review of other studies, gray literature) [Update 9/8/2021: corrected for #4 being a meta-analysis rather than original research. List above has been updated as well]

Claim Ref. # Study Type Claim Ref. # Study Type
1 Original research 25 Synthesis review of other studies
2 Scoping review of other studies 26 Mathematical model
3 Meta-analysis of other studies 27 Systematic review of other studies
4 Meta-analysis of other studies 28 Systematic review of other studies
5 Systematic review of other studies 29 Meta-analysis of other studies
6 Original research 30 Original research
7 Original research 31 Original research
8 Original research 32 Duplicate of #5 & #41
9 Original research 33 Original research
10 Original research 34 Original research
11 Original research 35 Original research
12 Original research 36 Original research
13 Original research 37 News article
14 Original research 38 Duplicate of #28
15 Original research 39 Duplicate of #29
16 Original research 40 Duplicate of #30
17 Blog review of other studies 41 Duplicate of #5 & #32
18 Duplicate of #17 42 Original research
19 Systematic review of other studies 43 Duplicate of #33
20 Letter/opinion review of other studies 44 Duplicate of #35
21 Original research 45 Original research
22 Original research 46 Original research
23 Original research 47 Duplicate of #46
24 Original research

Finally, I cross-referenced the two tables to see if there were any patterns between the groups and I didn’t identify any.

  • Of the four links that supported the claim that masks were ineffective/useless, two were meta-analyses of other studies and two were original research.
  • Of the 24 links that found masks were effective at reducing the spread of COVID at least some, six were literature reviews (scoping, systematic, and meta-) and the remaining 18 were original research.
  • Of the six where I couldn’t get the full paper, one was a systematic review of other studies and the other five were original research.
  • The remaining four were gray literature and/or not applicable to the claim at hand.

I will add my review details below this point as time allows. The details will include any statement from the LifeSiteNews author, a link to the publicly available full text if available, the study title, and my assessment of why the study does or does not support the false claim that masks are ineffective/useless.


Claim #1

The US Centre for Disease Control performed a study which showed that 85 percent of those who contracted Covid-19 during July 2020 were mask wearers. Just 3.9 percent of the study participants never wore a mask. (emphasis added)

Study title and link: Community and Close Contact Exposures Associated with COVID-19 Among Symptomatic Adults ≥18 Years in 11 Outpatient Health Care Facilities — United States, July 2020

Study type: Original research

What the study actually found: First, the study was not designed to measure the effectiveness or lack thereof of masking. The goal of the study was to determine whether there were places that study participants visited that resulted in more or less likelihood of having COVID-19 symptoms. What the study found was that people visiting bars and restaurants – places where masking is difficult if not impossible – were the most likely to come down with COVID. In other words, the researchers found indirect evidence that masks are probably effective, which is opposite the false claim that masks are ineffective/useless. [Ed. note: I debunked this one previously at this link.]

Second, if you review the emphasized sections of the claim above, you’ll see that there’s a subtle difference in language between the two. The first is written in a way that suggests it applies to everyone in the US, while the second is strictly limited to the study participants. Lots of people have assumed that the 85% claim applies universally, which the study does not say. In fact, the study explicitly says that the results may not be representative of the larger US population. This makes the claim misleading.

Conclusion: The study does not support the claim that masks are ineffective/useless, and the claim as written is misleading.


Claim #2

This study used 5462 peer-reviewed articles and 41 grey literature records.

“Conclusion: The COVID-19 pandemic has led to critical shortages of medical-grade PPE. Alternative forms of facial protection offer inferior protection. More robust evidence is required on different types of medical-grade facial protection. As research on COVID-19 advances, investigators should continue to examine the impact on alternatives of medical-grade facial protection”

So how is your cloth and surgical mask working again if EVEN medical grade alternatives are failing ?

Study title and link: Facial protection for healthcare workers during pandemics: a scoping review

Study type: Scoping review

What the study actually found: First, the study did not use “5462 peer-reviewed articles and 41 grey literature records.” That was the starting point for the scoping review. It was filtered down, like all literature review are, to 48 peer-reviewed studies and 19 gray literature records, for a total of 67.

Second, the authors concluded that most of the studies they reviewed didn’t have enough data on improvised masks to draw any firm conclusions, but that 10 studies found that improvised masks were better than no mask at all.

Third, the authors wrote the following (emphasis added): “Evidence supports the superiority of medical-grade masks for protection against respiratory viruses. In cases when medical-grade masks are not available, the summarised research indicates that protection offered by certain improvised or reused masks is better than no protection at all.”

Conclusion: The study does not support the claim that masks are ineffective/useless, and the claim as written is misleading.


Claim #3

“There is moderate certainty evidence that wearing a mask probably makes little or no difference to the outcome of laboratory-confirmed influenza compared to not wearing a mask”

Study title and link: Physical interventions to interrupt or reduce the spread of respiratory viruses

Study type: meta-analysis

What the study actually found: This study reviewed multiple other original research studies and focused on three different infection types – laboratory confirmed influenza, unconfirmed influenza-like illnesses, and any respiratory viral illness. And the results they found varied depending on the type of infection.

For lab-confirmed influenza, the reduction in cases in mask wearers over non-mask wearers had a wide confidence interval that overlapped the risk ratio value of 1 (in this case, the risk ratio is the number of mask wearers who got sick divided by the number of non-mask wearers who got sick). The study’s authors concluded that this result had a decent chance of being accurate after they made several assessments of bias in the studies.

For influenza-like illnesses, the authors found with a confidence interval of 85% that masks reduced risk, but they also concluded that the referenced studies were less likely to be accurate due to their bias assessments

And for all viral infections, the confidence interval was the lowest of all, but the confidence in the results was also very low.

Conclusion: The study does support the claim that masks are are ineffective/useless.


Claim #4

“We included three trials, involving a total of 2106 participants. There was no statistically significant difference in infection rates between the masked and unmasked group in any of the trials”

Study title and link: Disposable surgical face masks for preventing surgical wound infection in clean surgery

Study type: meta-analysis (initially classified as original research in error – corrections made to summary information above)

What the study actually found: First, the criteria used by the study’s authors were very restrictive. While the study was an update to a study originally performed in 2002, this 2016 update found only three original research studies that met their criteria. This is a very small number for a meta-analysis and limits the applicability of their conclusions.

Second, the three studies included in the meta-analysis were from 1984, 1991, and 2010. While the authors don’t address this particular point, there are likely differences in mask construction and materials over the course of the 26 year span of the three studies, and there may have been changes in surgical protocols that have an impact on wound infection. Such details may, or may not, affect the results of the meta-analysis.

These concerns do alter the conclusion of the meta-analysis, however, which is that there is no evidence of masks being effective at reducing surgical wound infections.

Conclusion: The study does support the claim that masks are are ineffective/useless.


Claim #5

Two randomized controlled trials were included involving a total of 1453 patients. In a small trial there was a trend towards masks being associated with fewer infections, whereas in a large trial there was no difference in infection rates between the masked and unmasked group.

Study title and link: Disposable surgical face masks: a systematic review

Study type: Systematic review

What the study actually found: I was unable to locate a full copy of the paper. As an observation, one of the study’s authors is the same as one of the authors of the study referenced in Claim #4 above.

Conclusion: No way to assess whether the full study does or does not support the claim that masks are ineffective/useless.


Claim #6

“Our results suggest that cloth masks are only marginally beneficial in protecting individuals from particles < 2.5 μm”

Study link and title: Evaluating the efficacy of cloth facemasks in reducing particulate matter exposure

Study type: original research

What the study actually found: This is a study of multiple different types of cloth masks as well as surgical masks and N95-style masks.

First, the study found that there was significant variation between different types of cloth masks, and as you would expect, all the masks filtered better at the low flow rate (essentially breathing while sitting) vs at the high flow rate (essentially light to moderate activity).

Second, the study found that there was significant variation in effectiveness of masks at different particle sizes. Smaller particles made it through the mask more easily than larger particles. Particles of the size of a single SAR-CoV-2 virus (~ 100 nm) were filtered better by the N95 masks (80%+ filter efficiency at both flow rates) and surgical masks (60-70% filter efficiency at high flow and 90%+ at low flow) than by two of the three cloth masks tested (30-40% filter efficiency at high flow and 50-70% at low flow). But one of the cloth masks was as good at filtering virus-sized particles as the N95 mask was.

Third, effectiveness of cloth masks improved with larger particles, just as it did with the N95 and surgical masks.

The authors had this to say as well: “Overall, cloth facemasks lead to a measureable reduction of total particle counts. However, there was variability among the performance of cloth masks and also among different particle sizes.” In every case, masks were better than no masks.

Conclusion: The study does not support the claim that masks are ineffective/useless.


Claim #7

“The filtration efficiency of the filter materials was good, over 95%, for particles above 5 micron in diameter but great variation existed for smaller particles.”

Coronavirus is 0.125 microns. therefore these masks wouldn’t protect you from the virus

Study link and title: Face seal leakage of half masks and surgical masks

Study type: original research

What the study actually found: I was unable to locate a full copy of the paper to reveiw.

Conclusion: No way to assess whether the full study does or does not support the claim that masks are ineffective/useless.


Claim #8

“The filter efficiencies against influenza virus particles were the lowest”

“We conclude that the filter efficiency test using the phi-X174 phage aerosol may overestimate the protective performance of nonwoven fabrics with filter structure compared to that against real pathogens such as the influenza virus”

Study link and title: Comparison of the Filter Efficiency of Medical Nonwoven Fabrics against Three Different Microbe Aerosols

Study type: original research

What the study actually found: The study tested two different surgical mask materials to determine if three different microbes would penetrate them – a virus that infects bacteria (a “phage”) that was 14 nm, deactivated influenza in the range of 40-200 nm (average of 68 nm), and a bacterium that averaged 358 nm but some of which were bigger than 1 μm. The deactivated influenza virus is the closest in size to the SARS-CoV-2 virus, but the bacterium could serve as a stand-in for larger droplets containing lots of viruses.

The study found that tests that both surgical mask materials were good at blocking the phage and the bacterium weren’t as good at blocking the deactivated influenza virus. One material was only 20% effective at blocking the flu, but the other was 80% effective.

The authors also point out that the influenza virus is small when compared to other viruses that infect people, so the results for influenza might or might not be applicable to other, larger viruses. And while one material’s filter efficiency was low, it wasn’t so low as to indicate that the mask was ineffective or useless given SARS-CoV-2 is not spread just by individual viruses.

Conclusion: The study does not support the claim that masks are ineffective/useless.


Claim #9

“Although surgical mask media may be adequate to remove bacteria exhaled or expelled by health care workers, they may not be sufficient to remove the submicrometer-size aerosols containing pathogens ”

Study title and link: Aerosol penetration through surgical masks

Study type: original research

What the study actually found: The purpose of this 1992 study was to assess how effective surgical masks were for particles in the range of 150 nm to 4 μm and tested over aiflow ranges from 5 to 100 L/min (from resting to heavy exertion). They studied surgical masks that have a filter layer (the standard today) as well as masks that did not.

The first finding was that there is greater penetration of the mask at higher flow rates, but that for particles larger than about 2 μm the mask with the filter blocked nearly everything regardless of the flow rate.

The second finding was that the surgical mask with the filter was effective at filtering particles all the way down to 150 nm. At 100 L/min (heavy exertion) the worst filtering was about 30% for 400 nm particles, but at 5 L/min (resting) the worst filtering was about 65% at 700 nm. For SARS-CoV-2 virus-sized particles, the worst filtering effectiveness was 35% at 100 L/min and went up to 80% at 5 L/min.

Something to keep in mind is that this study was intended to determine how well surgical masks protected the wearer, not the people around them. Regardless, the study showed that surgical masks were effective at particle sizes similar and larger than SARS-CoV-2 virues.

Conclusion: The study does not support the claim that masks are ineffective/useless.

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