This is Yves. Lambert was very pleased to see that a team led by Oxford’s innocuous Trish Greenhalgh decisively bombed the bizarre and destructive anti-mask campaign, with the Cochrane report debunked (but only after been widely praised). example. Greenhalgh and his fellow scientists made the logical decision to exclude studies that did not investigate the effectiveness of masking, such as those in which participants removed their masks while still indoors, or worse, treated various public initiatives aimed at wearing masks as if they produced appropriate mask use. A key sentence from the post below: “Most RCTs of public mask wearing were actually trials of mask wearing advice. »
I would have included the study below, which KLG and Ignacio deemed masterful, at the end of the post, but the file size is too large. You can find it here.
And thank you for spreading this post widely!
By Trish Greenhalgh, Professor of Primary Care Health Sciences, University of Oxford; C Raina MacIntyre, Professor of Global Biosecurity, NHMRC L3 Research Fellow, Biosecurity Program Manager, Kirby Institute, UNSW Sydney; and David Fisman, professor in the Division of Epidemiology at the University of Toronto. Originally published on The conversation
When a Texas farm worker recently caught bird flu from livestock, social media was full of rumors. Although avian flu is not a human pandemic, scientists and policymakers around the world want to prepare as best they can for the emergence of such a pandemic. difficult task, given that science is complicated, policy must be pragmatic, and people’s values do not always align.
It’s time for masks to enter the chat. At the start of a pandemic caused by a new or newly mutated virus, there may be no vaccine, no clear knowledge of the magnitude of the situation, and no specific treatment. It will be essential to slow transmission until more is known.
Getting most people to wear masks could nip the outbreak in the bud, thereby preventing a pandemic or lessening its impact. Wearing a mask is inconvenient, but not as inconvenient as confinement.
But do masks work? A goodbye masks and respirators, which only focused on clinical trials, concluded that there was not enough evidence to assess whether wearing a mask reduced the risk of spreading or contracting respiratory illnesses. However, we do not agree with this.
The study, carried out by the nonprofit Cochrane Collaboration, failed to influence recent guidance issued by the United States. Centers for Disaster Control and Prevention (CDC) in response to troubling news regarding the transmission of avian influenza to humans. The CDC has recommended properly fitted respirators – as well as coveralls and safety glasses – for anyone working with potentially infected livestock until the threat of bird flu subsides.
Is this latest guidance based on solid evidence? According to our new examination of the evidence, Yes. Like the Cochrane team, we pooled data from randomized controlled trials (RCTs) and analyzed the combined data – this is called a meta-analysis.
Unlike them, we also looked at non-RCT evidence, including dozens of laboratory studies that showed that respiratory infections, including the common cold, COVID, flu, measles, and tuberculosis, spread . mainly by air.
Laboratory evidence has shown that different mask materials filter tiny particles better or worse and are more or less breathable, especially when wet. This explains why a cloth or paper mask soaked with moisture from exhaled air becomes more difficult to breathe and may be less protective.
While medical masks are usually tied loosely around the face (so air can bypass the filter), respirators fit snugly and if worn at work it should be tested to ensure all air inhaled or exhaled passes through a high quality filter.
All this non-RCT evidence is of crucial importance for the design of RCTs. Since respiratory viruses float in the air, to be optimally effective, a mask must be made of a highly filtering material and must fit well. It should not be removed indoors, otherwise the person will be immediately exposed to infectious particles in the air.
It follows that RCTs of poorly designed masks, poorly fitted masks, or masks worn only occasionally should not be expected to show an effect. Nor should we expect simple advice to wear a mask to have any effect if it is not followed.
Finally, when comparing respirators with masks in places where there is a high risk of infection, such as a hospital, the respirator must be worn at all times. until the person leaves the buildingand not just occasionally during so-called “aerosol-generating” procedures – such as intubating a patient.
If we consider these crucial details of RCT design, rather than simply comparing experiments with and without masks, we find that masks are effective, and respirators even more effective, in reducing the spread of respiratory disease. We can also explain why some previous reviews seemed to show that this was not the case.
Most RCTs of public mask wearing were actually trials of mask wearing advice. In both RCTs and observational studies (such as real-world experiments), there was a dose-response effect: the more people wore their masks, the more effective the masks proved. And when a pandemic approaches, people tend to wear their masks.
The essential
When we looked at RCTs, we found that masks do protect in the community and that N95 respirators (masks made from premium filtration material and designed to fit tightly around the face to protect against airborne contaminants) are superior to masks used by healthcare workers. especially when respirators were worn at all times at work. Non-randomized evidence also shows that masks work and that respirators work better.
Let’s hope we’re not heading into another pandemic. But while we consider this possibility, the main focus of our recent review is the work of masks. In addition to improving indoor air quality and avoiding overcrowded and under-ventilated places, they are the best way to avoid getting a respiratory infection. And our results confirm previous advice not to wear just any mask, but wear the best mask available.
