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This article was originally published on May 22, 2024 and is being republished Independent As Britain grapples withtidal waveAbout the disease this flu season
When a Texan farm worker caught bird flu Recently from cattle, social media It was full of rumours. Although bird flu is not a human pandemic, scientists and policymakers around the world are keen to prepare as best they can if such a pandemic emerges – a difficult task, given that the science is messy, policy must be pragmatic and people’s values do not always align.
its time has come mask To enter the chat. At the beginning of a pandemic caused by a new or newly adapted virus, there may be no vaccine, no firm knowledge of how bad things will be, and no specific treatment. It will be important to slow down transmission until more information is known.
Inspire most people to wear mask This can stop the epidemic in its beginning, stop the epidemic or reduce its impact. Wearing a mask is inconvenient, but not as inconvenient as lockdown.
But do masks work? The review of masks and respirators, which only looked at clinical trials, concluded that there was not enough evidence to assess whether wearing masks reduces the risk of spreading or contracting respiratory diseases. However, we disagree with this.
The review, conducted by the nonprofit Cochrane Collaboration, failed to influence recent guidance issued by the U.S. Centers for Disease Control and Prevention (CDC) in response to the disturbing news of the transmission of bird flu to humans. The CDC recommends a well-fitting respirator — along with overalls and safety goggles — for anyone working with potentially infected cattle until the risk of bird flu subsides.
Is this latest guidance based on solid evidence? According to our new review of the evidence, yes. Like the Cochrane team, we collected data from randomized controlled trials (RCTs) and analyzed the combined data – a so-called meta-analysis.
In contrast to them, we also examined non-RCT evidence, including dozens of laboratory studies, that showed that respiratory infections, including the common cold, COVID, flu, measles, and TB, spread primarily through the air.
Laboratory evidence has shown that different mask materials are better or worse at filtering small particles, and more or less breathable – especially when moist. This explains why a cloth or paper mask that becomes wet from moisture in exhaled air becomes harder to breathe through and may be less protective.
While medical masks are typically tied loosely around the face (so air can bypass the filters), respirators fit snugly and if worn at work should be fit-tested to ensure that all air inhaled or exhaled passes through high-grade filters.
All of this non-RCT evidence is extremely important for the design of RCTs. Since respiratory viruses float in the air, to be maximum effective, masks must be made of high-filtration materials and fit closely. It should not be removed indoors otherwise the person will immediately be exposed to infectious particles in the air.
About the authors
Trish Greenhalgh is Professor of Primary Care Health Sciences at the University of Oxford
C Raina McIntyre Professor of Global Biosecurity, NHMRC L3 Research Fellow, heads the Kirby Institute’s Biosecurity Program at UNSW Sydney.
David Fisman is Professor in the Department of Epidemiology at the University of Toronto.
This article is republished from Conversation Under Creative Commons license. read the original article,
This means that we should not expect RCTs to show efficacy of poorly designed masks, ill-fitting masks, or masks that are worn infrequently. Nor should we expect that the mere advice of wearing a mask will have any effect unless it is followed.
Finally, when comparing respirators with masks in settings where the risk of infection is high, such as hospitals, respirators should be worn continuously until the person leaves the building, rather than worn only occasionally when performing so-called “aerosol-generating procedures” – such as intubating a patient.
If we take these important details of RCT design into account, rather than simply comparing mask-on, mask-off experiments, we find that masks are effective in reducing the spread of respiratory disease, and respirators even more effective. We can also explain why some previous reviews made it seem like this was not the case.
Most RCTs of mask wearing by the public were actually tests of the advisability of mask wearing. 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 turned out to be. And when a pandemic breaks out, people prefer to wear masks.
bottom line
When we looked at RCTs, we found that masks protect in the community, and N95 respirators (masks made using high-grade filtration materials and designed to fit closely around the face to protect against airborne contaminants) are superior to masks in health care workers, especially when the respirators are worn continuously at work. Non-RCT evidence also shows that masks work and that respirators work better.
Let’s hope we’re not headed for another pandemic. But as we consider that possibility, our recent review concludes that masks work. Along with improving indoor air quality and avoiding crowded, poorly ventilated spaces, they provide the best way to avoid respiratory infections. And our findings support previous advice to wear not just any mask, but the best mask available.