Share this page!

Enter URL or ID to Unroll

You can paste full URL like: https://x.com/threadreaderapp/status/1644127596119195649
or just the ID like: 1644127596119195649

How to get URL link on X (Twitter) App

  1. On the Twitter thread, click on or icon on the bottom
  2. Click again on or Share Via icon
  3. Click on Copy Link to Tweet
  4. Paste it above and click "Unroll Thread"!
  5. More info at Twitter Help
Trisha Greenhalgh Profile picture
@trishgreenhalgh
May 22 • 48 tweets • 14 min read • Read on X
It’s out! Our new state-of-the-science review of MASKS/RESPIRATORS in reducing transmission of respiratory infections. 13 authors (for our disciplines, see posts 3-4). 38000 words. 413 references. One conclusion: these devices work. For detail, read on. 1/
journals.asm.org/doi/10.1128/cm…
The commissioned review, which was independently peer-reviewed, had 3 objectives: 1. Summarize the evidence on masks/masking. 2. Examine why this evidence is so widely misunderstood, misinterpreted, or dismissed. 3. Outline an agenda for future research. 2/
Author team was chosen for breadth of expertise, including: public health, epidemiology, infectious diseases, biosecurity, fluid dynamics, materials science, mathematical modeling, data science, clinical trials, sociology, anthropology, psychology, and occupational hygiene. 3/
Author team, which includes @DALupton @DFisman @AmandaKvalsvig @globalbiosec @ShovonBhattach2 @joevipond and others from @kirbyinstitute @mark_ungrin @sameo416, also had expertise in multiple kinds of evidence synthesis, including statistical meta-analysis. 4/
@DALupton @DFisman @AmandaKvalsvig @Globalbiosec @ShovonBhattach2 @joevipond @KirbyInstitute @Mark_Ungrin @sameo416 Study protocol for this narrative review with embedded meta-analysis was registered on INPLASY: 5/inplasy.com/inplasy-2024-1…
@DALupton @DFisman @AmandaKvalsvig @Globalbiosec @ShovonBhattach2 @joevipond @KirbyInstitute @Mark_Ungrin @sameo416 We searched extensively for high-quality evidence in all fields. We did NOT assume that all RCT evidence was “gold standard”, nor that all non-RCT evidence was “low-quality”. Indeed, we questioned whether the RCT deserves its hallowed status in this field. 6/ the scientific value of the RCT has become inflated, particularly among doctors, leading them to overlook high-quality non-RCT evidence Overvaluing the RCT as a design also allows poor-quality RCTs (e.g., of intervention designs which do not take account of mechanism and which may therefore mislead rather than inform) to be published in high-impact journals and gain undue influence
@DALupton @DFisman @AmandaKvalsvig @Globalbiosec @ShovonBhattach2 @joevipond @KirbyInstitute @Mark_Ungrin @sameo416 We covered evidence across a vast range of disciplines and study designs, including but not limited to: laboratory studies, RCTs, observational studies, modelling studies, social and psychological studies, surveys, policy analyses, environmental impact studies. 7/
@DALupton @DFisman @AmandaKvalsvig @Globalbiosec @ShovonBhattach2 @joevipond @KirbyInstitute @Mark_Ungrin @sameo416 We went through the basic science showing that SARS-CoV-2, like other respiratory infections, is transmitted via the air. We criticised EPISTEMIC TRESPASSING by infection prevention & control (IPC) physicians, who drew wrong conclusions from their own flawed experiments. 8/ "IPC physicians unfamiliar with these techniques attempted and failed to isolate viable virus from air samples obtained in simple “cough bags” and interpreted their findings (erroneously) as evidence that there was no viable virus in the air"
@DALupton @DFisman @AmandaKvalsvig @Globalbiosec @ShovonBhattach2 @joevipond @KirbyInstitute @Mark_Ungrin @sameo416 We carefully traced the origins of the widely-propagated “droplet hypothesis”, in which it is assumed that large droplets somehow get deep into the lungs on some kind of ballistic trajectory (tip: they don’t). 9/ "For the same reason a motorcycle can negotiate a tighter corner than a laden truck moving at similar speed, larger particles collide with the walls of the upper respiratory tract and are deposited there and prevented from penetrating further by mucociliary clearance mechanisms"
@DALupton @DFisman @AmandaKvalsvig @Globalbiosec @ShovonBhattach2 @joevipond @KirbyInstitute @Mark_Ungrin @sameo416 Why does this matter? Because IF the droplet hypothesis were correct (TL;DR: it’s not), all we’d need is one of those baggy, waterproof-backed ‘medical masks’ designed to stop the surgeon sneezing into the patient’s open abdomen or getting a mouthful when an abscess bursts. 10/
But because respiratory infections transmit via TINY PARTICLES SUSPENDED IN THE AIR, waterproof-backed medical masks are NOT the best way to stop them. Starting from first principles, what we need is something that EFFICIENTLY REMOVES PARTICLES FROM THE AIR. 11/
In other words, not all things you put over your face are equal! Here’s a few things to think about: 12/


Image
Image
Image
Image
Are you with me? There are good ways and bad ways of designing a mask! Ideally, you want one that's guaranteed HIGH-FILTRATION, LOW-RESISTANCE, WELL-FITTING and SUPER-CLEAN. Such a device is known as a RESPIRATOR. 2 examples shown: N95 (single-use) & elastomeric (reusable). 13/
Image
Image
Did we address the anti-maskers’ favourite argument that the holes in a mask filter are bigger than the SARS-CoV-2 virus? What do you think? Of course we did. MASK FILTERS ARE NOT SIMPLE SIEVES! 14/ masks and respirators are not simple sieves. They use a variety of filter media which work in multiple ways, influenced by the size of the particle (85): Sedimentation of larger particles (1-10 um) under the influence of gravity. Inertial impaction, in which larger (above 1 um) particles are blocked by fibers in the filter matrix. Interception, in which medium-sized particles (smaller than 0.6 um) following the airflow collide with fibers. Diffusion, in which smaller lighter particles (0.02-0.40 um) impact fibers with Brownian motion. Electrostatic effects, in which particles passing near e...
Here’s a nice diagram. Each little square is a different laboratory study. ‘Filtering facepiece’ means RESPIRATOR. ‘Community mask’ means one you made at home (from cloth). ‘Protection factor’ (note: LOGARITHMIC scale) is how much it blocks bad particles (higher is good). 15/ Filtering face piece respirators have 1-100 times the protection factor as medical masks, which are slightly more protective than community masks
The above diagram is from Schmidt & Wang’s paper on the CRITICAL ROLE OF LEAKAGES in mask malfunction. If air leaks out around the sidesless protection. We thank these authors for letting us reproduce it. 16/ onlinelibrary.wiley.com/doi/full/10.11…
Another leakage study. Up the side is LEAKAGE (more is bad). Along the bottom is particle size. Different colours represent different masks: GREEN = medical mask (very leaky), PURPLE = respirator sealed all around with tape to get perfect fit (nothing gets through it). 17/ Very pretty graph showing that medical masks are really leaky and respirators hardly leak at all.
Credit for the previous image: Bagheri et al’s GOLD STANDARD laboratory study, which you can admire in full text here. Thanks to them for permission to reproduce. 18/ pnas.org/doi/abs/10.107…
OK, we’re getting to the RCT section. And this is where the quality of much of the evidence plummets—partly because there’s some flaky trials out there and partly because even the BEST trials of masks are INHERENTLY problematic.19/
Image
These criteria are extremely difficult to meet in trials of masking. Some scholars have argued that RCTs have major limitations in answering questions about the efficacy of masking (137). For example, real-world effects (such as poor compliance) in an intention-to-treat analysis of a trial conducted in a non-pandemic context may not reflect effectiveness in a pandemic, where it is more likely that masks would be worn as intended
Most RCTs of masks didn’t use an optimally-designed device. Many didn’t measure whether the mask was worn (where compliance *was* measured, was low). These flaws are like doing a RCT of a blood pressure drug at 1/100th the correct dose. They BIAS THE RESULT TOWARDS THE NULL. 20/
Other common flaws in mask RCTs include lack of power, suboptimal outcome measures, telling participants to only mask SOME of the time, and doing the study when there are no infections circulating. Each of these slip-ups will tend to bias results towards null. 21/
Small wonder, then, that most RCTs of masks in community or in healthcare settings produced no statistically significant difference between the ‘mask’ arm (actually, the “advice to slap a poorly-designed medical mask on if you feel inclined” arm) and the ‘no mask’ arm. 22/
The one adequately-powered RCT of community masking in the entire sample (which cluster-randomised villages in Bangladesh), by Abaluck et al, showed a statistically significant effect in favour of masks even though compliance was low. 23/ science.org/doi/full/10.11…
Let’s talk about RCTs of masks v respirators in healthcare. The research q here is of the utmost importance. Should we protect our staff with the kind of device that produced the purple line in post 17 above? Or should they get the device that produced the green (leaky) line? 24/
Here’s where the study designs go embarrassingly off. Because many IPC doctors falsely believe the droplet hypothesis (see post 9), their prior belief (which influences the intervention design) is that medical masks are as good as anything else so long as you wash your hands. 25/
IPC docs may also believe that infectious aerosols are produced by a patient only when they’re having a fancy procedure done to them by a doctor (hence ‘aerosol-generating medical procedure’ AGMP). (You’re right, it does rather smack of infantile omnipotence) 26/
In fact, patients infected with SARS-CoV-2 (or SARS-1 or MERS or influenza or measles or TB) emit infectious particles in the air by COUGHING and SPEAKING and even BREATHING. And those particles quickly spread THROUGHOUT THE INDOOR SPACE. 27/
Hence, any trial of masks v respirators in a healthcare setting MUST require the devices to be worn CONTNUOUSLY WHEN INDOORS. If higher-grade protection is worn only when close to a known ‘case’ or when doing an AGMP, it’s likely to be as good as a chocolate teapot. 28/
We meta-analysed mask-v-respirator trials in healthcare settings in 2 ways. First, lumping all trials together (result: respirators outperform masks *a bit*). Second, using only RCTs testing CONTINUOUS USE OF RESPIRATORS. Result: respirators outperform masks *significantly*. 29/
Acknowledging the limitations of observational evidence, we identified and summarised LOTS of observational studies and natural experiments. All studies pointed in the same direction: in favour of the kinds of effect you’d predict from basic science. 30/
pubmed.ncbi.nlm.nih.gov/34783656/#:~:t…
Likewise with mathematical modelling studies (of which there are various kinds). In sum, the non-RCT evidence – rather surprisingly and very consistently – stacks up in favour of masks (and of respirators as even better). 31/ This evidence is all the more remarkable as there are several reasons to expect that the direction of biases in observational epidemiological studies of masks and respirators would be toward the null
HARMS of masks. Three kinds: 1. Complete fictions (things the anti-maskers make up, like accumulation of poisonous CO2 in your body—it doesn’t happen). 2. Minor hazards (headaches, acne), which may be worth the trade-off. 3. Specific exemption conditions (see pic). 32/ Image
When OTHERS are masked, there may be communication problems, especially for D/deaf people. One of our authors, @AmandaKvalsvig, is hearing-impaired. She wrote: it MAY NOT be in a deaf person’s interests if others remove their masks! (It may, but need to WEIGH UP RISKS). 33/
We need better communication strategies that can be employed if mass masking needs to be introduced again. We talk about some avenues for this in the paper (e.g. lapel mics so we don’t tire out our voices). More research needed on these! 34/
WHY DO PEOPLE MASK (and why do some REFUSE TO MASK)? Answer: for lots of psychological, cultural, ideological and social reasons, as @DAlupton says in her section. 35/
Image
masking and support for it have declined, raising societal and ethical questions about whether and for how long the healthy majority should compromise their “freedom” to help protect the clinically vulnerable (for whom a COVID-19 infection could be life-threatening) and prevent the long-term sequelae of the condition
Misleading messages from leading public health agencies contributed to confusion about masks and about the relative benefits of respirators versus medical masks. 36/ Image
Mask POLICIES involve strongly recommending and even mandating the wearing of masks in certain settings. We do a long section on this. Policymakers need to ASSESS THE RISKS, BALANCE THE TRADE-OFFS and SUPPORT THE POLICY (e.g. by giving them away). 37/
Single-use masks and respirators are not good for the planet. It’s time we moved to a more sustainable approach. Re-usable, recyclable and biodegradable devices exist. DID YOU KNOW that you can recycle chopped-up masks to make building materials like concrete? 38/
Time for conclusions. First, MASKS WORK!!! And we’ve explained why some people insist that they don’t! Read the yellow bit out loud please. 39/ 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
Second conclusion. It’s time to REMOVE PEOPLE WHO CAN’T OR WON’T UNDERSTAND THE EVIDENCE ON MASKING FROM KEY DECISION-MAKING COMMITTEES. Who will be brave and make that move? Lives depend on it. 40/ Second, given that masking is an effective (though not perfect) intervention for controlling the spread of respiratory infections, and that it may be particularly important in the early stages of pandemics (when the pathogen may be unknown and drugs and vaccines are not yet available), improving understanding among scientists, clinicians, policymakers and the public about the effectiveness of masks and respirators is an urgent priority. The continuing recalcitrance of many (though not all) in the infection prevention and control community on this issue could prove a major threat to public h...
Third conclusion. Mask policies should be based on ACTUAL risks, not SPECULATIVE ones. And masks, overall, should be better designed to REDUCE the minor side effects like hot face. 41/ Third, mask policies should better reflect the actual risks and harms of masks rather than being overly influenced by speculative risks (such as retention of carbon dioxide) that have no empirical foundation, or by adverse effects affecting certain defined groups (e.g., some people with autism) which could be covered by exemptions. Rather, the focus should be on supporting effective mask use by addressing well-described and widely experienced adverse effects of masking such as communication difficulties, physical discomfort, and skin reactions. Communication is a vital human need, so commun...
Fourth conclusion. Talking of design, we need CREATIVE DESIGNS to suit EVERYONE, not just your standard crash-dummy white 70Kg clean-shaven male. 42/ Image
Fifth conclusion. Let’s make masks sustainable. 43/ Image
Final conclusion: anti-mask disinformation is as dangerous as anti-vax disinformation. We need to systematically counter it. 44/ Image
BOTTOM LINE: We don’t need any more masks-on v masks-off RCTs. That’s for dobbins. We need a NEW GENERATION of research which takes as its starting point the VAST EXISTING EVIDENCE BASE on the efficacy of masks and respirators. Then this: 45/ Image
If you like this thread, please hit the retweet button! Thanks to @DALupton @DFisman @AmandaKvalsvig @globalbiosec @ShovonBhattach2 @joevipond and others from @kirbyinstitute @mark_ungrin @sameo416. 46/
@DALupton @DFisman @AmandaKvalsvig @Globalbiosec @ShovonBhattach2 @joevipond @KirbyInstitute @Mark_Ungrin @sameo416 And here’s the pice on my Departmental website 47/phc.ox.ac.uk/news/comprehen…
@DALupton @DFisman @AmandaKvalsvig @Globalbiosec @ShovonBhattach2 @joevipond @KirbyInstitute @Mark_Ungrin @sameo416 And here's our piece for The Conversation - also just out (you can syndicate): 48/
theconversation.com/masks-work-our…

• • •

Missing some Tweet in this thread? You can try to force a refresh
　

Keep Current with Trisha Greenhalgh

Trisha Greenhalgh Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

PDF

Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @trishgreenhalgh

Trisha Greenhalgh Profile picture
Aug 1
Thread on our new state of the science review on #LongCovid. Commissioned by @TheLancet, peer-reviewed, coauthored with @sivanmanoj, @calirunnerdoc and Janko Nikolich. Link for free access is here (after 50 days that won’t work, then you’ll have to register and use this one:
1/kwnsfk27.r.eu-west-1.awstrack.me/L0/https:%2F%2…
thelancet.com/journals/lance…
In writing this article, we wanted to get the basic science of Long COVID into dialogue with the clinical management of this condition and the patient lived experience. @calirunnerdoc brought lived experience to our author team. 2/ Image
@calirunnerdoc Most but not all definitions of Long COVID put the cut-off at around 12 weeks (that is, if you’re still symptomatic 12 weeks after your initial COVID-19 infection, you’ve got Long COVID). 3/ Image
Read 21 tweets
Trisha Greenhalgh Profile picture
Mar 18
BREAKING
The senior officers of the Royal College of Physicians commissioned a survey of MRCPs’ views on physician associates (PAs). They have today released the actual findings, but the back story is shocking. I’ll link to the raw data at the end of this 🧵.
1/
We now know that senior officers presented a flawed and distorted version of the findings at the Extraordinary General Meeting on 13th March 2024. Here’s my thread on that presentation (from before I’d seen the actual results).
2/
Of note is that after an outcry, the senior officer who presented the slides at the EGM resigned. He can tell his own story there. I am hearing he did not make the slides but was told he had to present them.
3/
Read 25 tweets
Trisha Greenhalgh Profile picture
Mar 14
At yesterday’s #RCPEGM, a senior officer presented the results of a survey of MRCPs on their views about Physician Associates (PAs). They unwittingly supplied some good teaching material about how NOT to go about doing a questionnaire survey and how NOT to report the results. title slide 'RCP membership survey'
Here’s the first slide after the title slide. What do you notice? They jump straight into “methodology”. Students, don’t do this! Start with a RESEARCH QUESTION!! You must be clear what EXACTLY you want to find out, and from whom. Ideally, state some HYPOTHESES. "methodology" slide lacking research q
Here's the six questions that were sent out to MRCPs. Notice how the choice of words narrows the issue being explored. No Qs are asked about primary care (where PAs are seeing undifferentiated patients), yet RCP seeks to certify PAs for working in primary care. Six questions 1. How do you feel about physician associates being part of the MDT? 2. In secondary care, do you feel that you, or doctors you work with, are appropriately supervised and supported? 3. In secondary care, in your opinion, do you think physician associates are appropriately supervised and supported? 4. Does having a physician associate on your team impact on training opportunities for you? 5. Does working with a physician associate impact on training opportunities for doctor colleagues in your team? 6. Within your MDT, how well understood is the term ‘physician associate’?
Read 11 tweets
Trisha Greenhalgh Profile picture
Dec 29, 2023
Our new paper:
‘Training needs for staff providing remote services in general practice: a mixed-methods study’, out today in @BJGPjournal
🧵 1/

bjgp.org/content/74/738…
Around one in 4 consultations in general practice occurs remotely (usually by telephone but sometimes as video or asynchronous e-consultation). Appointment booking and triage usually occur remotely too.
2/
Since the pandemic began, UK policy (especially English policy) has swung from ‘remote by default’ to ‘everyone has a right to a face to face consultation’. GP land is busy, has major workforce issues (esp not enough doctors) and is creaking under the strain of task-shifting.
3/
Read 23 tweets
Trisha Greenhalgh Profile picture
Nov 29, 2023
Our paper on safety in remote GP consultations is getting a lot of coverage. Shout out to @oohGPwales who was lead author and analysed the 95 tragic safety incidents.
1/ 🧵
But NOTE: this paper is MAINLY about how remote care in GP land is remarkably SAFE. We followed 12 GP practices for 2y, looking for (among other things) evidence of patient harm from remote consultations. We found NONE.
2/
Staff in these 12 GP practices took a lot of measures to make sure that safety incidents didn’t happen. They often told patients “sorry you can’t have a phone consultation for that problem, you need to come and be examined”.
3/
Read 12 tweets
Trisha Greenhalgh Profile picture
Aug 6, 2023
At @IndependentSage we've made a series of short MYTHBUSTER videos to address misconceptions about covid-19.

I'll thread them here. Some are still to come - will add as they come out.

Please disseminate, especially to people who might be confused about these issues.

0/
Myth-buster 1: Is there a point to vaccines if we can still get infected?


1/
Myth-buster 2: Is "natural" immunity better than vaccine immunity?


2/
Read 9 tweets

Did Thread Reader help you today?

Support us! We are indie developers!

This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Don't want to be a Premium member but still want to support us?

Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal

Or Donate anonymously using crypto!

Ethereum

0xfe58350B80634f60Fa6Dc149a72b4DFbc17D341E copy

Bitcoin

3ATGMxNzCUFzxpMCHL5sWSt4DVtS8UqXpi copy

Thank you for your support!

Follow Us!

Send Email!

:(