Cochrane review on mask wearing

[Woodchopper]

New review published on 30 January.

In order to increase the number of studies it covers influenza as well as Covid. Concludes that there there is little high quality research and overall masks don’t appear to help, but hand washing does.

We obtained the following results:

Medical or surgical masks

Ten studies took place in the community, and two studies in healthcare workers. Compared with wearing no mask in the community studies only, wearing a mask may make little to no difference in how many people caught a flu-like illness/COVID-like illness (9 studies; 276,917 people); and probably makes little or no difference in how many people have flu/COVID confirmed by a laboratory test (6 studies; 13,919 people). Unwanted effects were rarely reported; discomfort was mentioned.

N95/P2 respirators

Four studies were in healthcare workers, and one small study was in the community. Compared with wearing medical or surgical masks, wearing N95/P2 respirators probably makes little to no difference in how many people have confirmed flu (5 studies; 8407 people); and may make little to no difference in how many people catch a flu-like illness (5 studies; 8407 people), or respiratory illness (3 studies; 7799 people). Unwanted effects were not well-reported; discomfort was mentioned.

Hand hygiene

Following a hand hygiene programme may reduce the number of people who catch a respiratory or flu-like illness, or have confirmed flu, compared with people not following such a programme (19 studies; 71,210 people), although this effect was not confirmed as statistically significant reduction when ILI and laboratory-confirmed ILI were analysed separately. Few studies measured unwanted effects; skin irritation in people using hand sanitiser was mentioned.

On the quality of data:

Our confidence in these results is generally low to moderate for the subjective outcomes related to respiratory illness, but moderate for the more precisely defined laboratory-confirmed respiratory virus infection, related to masks and N95/P2 respirators. The results might change when further evidence becomes available. Relatively low numbers of people followed the guidance about wearing masks or about hand hygiene, which may have affected the results of the studies.

Link to the review:
https://www.cochrane.org/CD006207/ARI_d ... ry-viruses

[bob sterman]

Given this...

Relatively low numbers of people followed the guidance about wearing masks or about hand hygiene, which may have affected the results of the studies.

...it might better be described as a review of the effectiveness of mask wearing guidance rather than mask wearing itself.

[shpalman]

In more than 300 pages of pdf it seems like the papers on mask wearing in the population during the covid pandemic are two of them, one of them being

Well it has a slightly different title compared to that earlier preprint but I assume the same authors didn't do two of them.

Normalizing Community Mask-Wearing: A Cluster Randomized Trial in Bangladesh Abaluck et al. (what's the "Yale School of Management"?)

(link to the BMJ editorial: "the research on this is sh.t, here's an example" for convenience)

and the other being the ref (66) Bundgaard mentioned here:

(66) Bundgaard: https://doi.org/10.7326/M20-6817 (this is the "one randomized controlled trial")
(63) Doung-ngern: https://doi.org/10.3201/eid2611.203003
(43) Krishnamachari: https://doi.org/10.1016/j.ajic.2021.02.002
(36) Lio: https://doi.org/10.1186/s12889-021-10680-5
(60) Xu: https://doi.org/10.2196/21372
(57) Wang: https://dx.doi.org/10.1136/bmjgh-2020-002794

Mask wearing and covid-19 incidence—Six studies with a total of 2627 people with covid-19 and 389 228 participants were included in the analysis examining the effect of mask wearing on incidence of covid-19 (table 1) [36,43,57,60,63,66]. Overall pooled analysis showed a 53% reduction in covid-19 incidence (0.47, 0.29 to 0.75), although heterogeneity between studies was substantial (I2=84%) (fig 5). Risk of bias across the six studies ranged from moderate [36,57,60,66] to serious or critical [43,63].

[shpalman]

Oh and thinking that influenza and covid behave in the same way brought you "four weeks behind Italy".

[Grumble]

Steve Novella is not impressed
https://sciencebasedmedicine.org/masks-revisited/

[IvanV]

Steve Novella is not impressed
https://sciencebasedmedicine.org/masks-revisited/

Worth spelling out his headline.

A recent Cochrane review, limited in scope and problematic in methodology, does not show that masks do not work, despite common misreporting.

Cochrane reviews are unfortunately sometimes problematic. Edzard Ernst was convincingly scathing about Cochrane reviews which appeared to show that acupuncture was useful for pain control, as a letter in the current Private Eye reminded us.

[Herainestold]

Masks work. We know that.
Double masking helped India to beat the Delta variant.

[Woodchopper]

Karla Soares-Weiser, Editor-in-Chief of the Cochrane Library, has stated:

Many commentators have claimed that a recently-updated Cochrane Review shows that 'masks don't work', which is an inaccurate and misleading interpretation.

It would be accurate to say that the review examined whether interventions to promote mask wearing help to slow the spread of respiratory viruses, and that the results were inconclusive. Given the limitations in the primary evidence, the review is not able to address the question of whether mask-wearing itself reduces people's risk of contracting or spreading respiratory viruses.

The review authors are clear on the limitations in the abstract: 'The high risk of bias in the trials, variation in outcome measurement, and relatively low adherence with the interventions during the studies hampers drawing firm conclusions.' Adherence in this context refers to the number of people who actually wore the provided masks when encouraged to do so as part of the intervention. For example, in the most heavily-weighted trial of interventions to promote community mask wearing, 42.3% of people in the intervention arm wore masks compared to 13.3% of those in the control arm.

The original Plain Language Summary for this review stated that 'We are uncertain whether wearing masks or N95/P2 respirators helps to slow the spread of respiratory viruses based on the studies we assessed.' This wording was open to misinterpretation, for which we apologize. While scientific evidence is never immune to misinterpretation, we take responsibility for not making the wording clearer from the outset. We are engaging with the review authors with the aim of updating the Plain Language Summary and abstract to make clear that the review looked at whether interventions to promote mask wearing help to slow the spread of respiratory viruses.

[Woodchopper]

Steve Novella is not impressed
https://sciencebasedmedicine.org/masks-revisited/

Worth spelling out his headline.

A recent Cochrane review, limited in scope and problematic in methodology, does not show that masks do not work, despite common misreporting.

Cochrane reviews are unfortunately sometimes problematic. Edzard Ernst was convincingly scathing about Cochrane reviews which appeared to show that acupuncture was useful for pain control, as a letter in the current Private Eye reminded us.

It seems to me that the Cochrane review is doing what Cochrane reviews do. I spent years pointing out to homeopaths and similar that there is a hierarchy of evidence and the lower down the hierarchy the more likely it is a that a finding in an article is incorrect. It doesn't appear that there are many randomized control trials, and the results from those are inconclusive.

We shouldn't be surprised because the most important questions are about whether encouraging people to wear masks or making it mandatory will affect community transmission of respiratory diseases. This isn't going to be an easy thing to study and comes with all the complexities of different amounts of compliance, not just whether or people follow the advice or rules, but how consistently and where, and are those who do what they are told more likely to be careful in other ways. Add to that the methodological difficulties in measuring community transmission and ethical issues around the control group.

This isn't to say that advice or rules around mask wearing were wrong. In the middle of a pandemic its reasonable to to ask people to do something that will probably help and has few side effects for the great majority of people. I wore masks when the public health authorities recommended it, but I stopped when they stated that it was no longer needed.

It would be good if we could get better evidence. There will likely be another pandemic in our lifetimes and it would be good to have a much better idea not just of the overall effectiveness but the optimal timing of interventions. I hope that the billions spent on medical research can include some funding for more studies on mask wearing.

[shpalman]

Masks and respirators for prevention of respiratory infections: a state of the science review

Trisha Greenhalgh, C. Raina MacIntyre, Michael G. Baker, Shovon Bhattacharjee, Abrar A. Chughtai, David Fisman, Mohana Kunasekaran, Amanda Kvalsvig, Deborah Lupton, Matt Oliver, Essa Tawfiq, Mark Ungrin, and Joe Vipond.
Clinical Microbiology Reviews e00124--23

https://journals.asm.org/doi/epub/10.1128/cmr.00124-23

This review was commissioned partly because of controversy around a Cochrane review which was interpreted by some people as providing definitive evidence that masks don’t work (9). Our extensive review of multiple streams of evidence from different disciplines and study designs builds on previous cross-disciplinary narrative reviews (233, 412) and aligns with the recent call from philosophers of science to shift from a “measurement framework” (which draws solely or mainly on RCTs) to an “argument framework” (which systematically synthesizes evidence from multiple designs including mechanistic and real-world evidence) (19). Using this approach, we have demonstrated a more nuanced set of conclusions, summarized below, and have revealed why certain inaccurate assumptions and defective reasoning about the science of masks and masking seem to have become widely accepted among certain groups.

We began by reviewing basic science evidence on the transmission of SARS-CoV-2 and other respiratory pathogens and showed that there is strong and consistent evidence that they spread predominantly by the airborne route. We also showed that masks are effective, and well-fitting respirators are highly effective, in reducing transmission of respiratory pathogens, and that these devices demonstrate a dose-response effect (the level of protection increases as adherence to masking increases).

We then provided a methodological critique of clinical trials of masks in the control of respiratory disease epidemics and outbreaks, including listing common design flaws. We summarized evidence from RCTs, including repeating methodologically flawed meta-analyses, and showed that respirators are significantly more effective than medical or cloth masks, especially (and to the extent that) they are actually worn in all potentially hazardous circumstances.

We also reviewed an extensive body of observational and modeling evidence which showed that, overall, masking and mask mandates are effective in reducing community transmission of respiratory diseases during periods of high community transmission. The observational findings are particularly striking since various inherent limitations of such designs are likely to bias findings toward the null.

Our review of adverse effects and harms of masks found strong evidence to refute claims by anti-mask groups that masks are dangerous to the general population. We also found that masking may be relatively contraindicated in individuals with certain medical conditions and that certain groups (notably D/deaf people) are disadvantaged when others are masked.

We summarized evidence from multiple countries and cultures which shows that masks are important sociocultural symbols about which people care deeply (positively or negatively). We also showed that adherence (and non-adherence) to masking is sometimes linked to political and ideological beliefs and to widely circulated mis- or disinformation, and hence hard to change.

... the claim that masks don’t work is demonstrably incorrect, and appears to be based on a combination of flawed assumptions, flawed meta-analysis methods, errors of reasoning, failure to understand (or refusal to acknowledge) mechanistic evidence, and limitations in critical appraisal and evidence synthesis