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In controlled lab situations, face masks appear to do a good job of reducing the spread of coronavirus (at least among hamsters) and other respiratory viruses. However, evidence shows that wearing a mask Strategies appear to have had much less impact on the community spread of COVID-19.
Why this gap between laboratory efficiency and efficacy observed in the community? The real world is more complex than a controlled laboratory situation. The right people need to wear the right mask, in the right way, at the right times and in the right places.
The actual impact of face masks on virus transmission depends not only on the behavior of the virus, but also on the behavior of aerosol droplets in various contexts and on the behavior of people themselves.
We performed a comprehensive review of the evidence on how face masks and other physical interventions affect the spread of respiratory viruses. Based on current evidence, we believe that the impact on the community is modest and that it might be better to focus on mask wearing in high risk situations.
Read more: How a 150-year experiment with a beam of light showed germs exist – and a face mask can help filter them out
The proof
Simply comparing the infection rates in people who wear masks with those who do not can be misleading. One problem is that people who don’t wear a mask are more likely to go to crowded spaces and less likely to socially move away. Those most affected often adhere to several protective behaviors – they likely avoid crowds and social distances as well as wearing masks.
This correlation between wearing a mask and other protective behaviors could explain why studies comparing mask wearers to non-mask wearers (called “observational studies”) show greater effects than those observed in testing. Part of the effect is due to these other behaviors.
The most rigorous, but difficult, way to assess the effectiveness of masks is to take a large group of people and ask some to wear masks and others not to, in a so-called controlled trial. . We found that nine such trials had been conducted for influenza-like illnesses. Surprisingly, when combined, these trials only found a 1% reduction in ILI cases in mask wearers compared to non-mask wearers, and a 9% reduction in confirmed influenza. in laboratory. These small reductions are not statistically significant and are likely due to chance.
Learn More: 13 Insider Tips on How to Wear a Mask Without Your Glasses Fogging, Running Out of Breath, or Sore Ears
None of these trials have studied COVID-19, so we cannot be sure if they are relevant to the pandemic. The SARS-CoV-2 coronavirus is similar in size to the flu, but has a different ability to infect people, so masks may be more or less effective for COVID-19. A recently published trial in Denmark involving 4,862 adults found that SARS-CoV-2 infection occurred in 42 participants randomized to receive masks (1.8%) compared to 53 control participants (2, 1%), a reduction (not significant) of 18%.
The most comprehensive cross-country study of masks for COVID-19 infection is a comparison of policy changes, such as social distancing, travel restrictions and the wearing of masks, across 41 countries. He found that the introduction of a mask-wearing policy had little impact, but mask policies were mainly introduced after social distancing and other measures were already in place.
The conversation, Author provided
What could reduce the effect of masks?
Why do masks not protect the person wearing them? There are several possibilities. Standard masks only partially protect your nose and mouth, for one thing. On the other hand, masks do not protect your eyes.
The importance of eye protection is illustrated by a study of community health workers in India. Despite protection by three-layer surgical masks, alcohol-based hand sanitizer, gloves and shoe covers, 12 of 60 workers developed COVID-19. Workers were then given face shields (which provide eye protection) – in addition to the personal protective equipment (PPE) described above – and none of the 50 workers were infected despite a higher case load. .
Why masks may not clearly protect others is more complex. Good masks reduce the spread of droplets and aerosols, and therefore should protect others.
Paul Glasziou, Author provided
However, in our systematic review, we found three trials that assessed how well wearing a mask protects others, but none of them found an obvious effect. Both trials in homes where a person with the flu wore a mask to protect others actually showed a slight increase in influenza infections; and the third trial, in college dorms, found a non-significant relative reduction of 10%.
We do not know if the failure was the masks or the membership of the participants. In most studies, adherence was low. In trials, very few people wear them all day (an average of about four hours per self-report, and even fewer when directly observed). And this membership has declined over time.
But we also have little research on how long a single mask will last. Most guidelines suggest around four hours, but bacteria studies show that masks provide good protection for the first hour and two hours are poor. Unfortunately, we were unable to identify similar research on viruses.
Dan Himbrechts / AAP
Is it better to focus the masks on the 3 Cs: covered, crowded and narrow contact?
In addition to the completed Danish trial, another ongoing trial in Guinea-Bissau with 66,000 participants randomized to entire villages could shed more light by testing the idea of source control. But given the millions of cases and billions of potential masks and mask wearers, further such trials are warranted.
We know that masks are effective in laboratory studies, and we know they are effective in the personal protective equipment of healthcare workers. But this effect appears to be diminished in community use. Thus, in addition to testing, further research is urgently needed to unravel each of the reasons why laboratory efficiency does not appear to have translated into community efficiency. We also need to find ways to bridge the gap.
Until we have the necessary research, we should be wary of using masks as a mainstay in preventing community transmission. And if we want people to wear masks regularly, we might be better off targeting high-risk situations for shorter periods of time. They are generally places described by “the three Cs”: congested places, places of close contact and confined and closed spaces. These would include certain workplaces and public transport.
We’ll probably be better off if we use a lot of new masks in the riskier environments, rather than moderate use everywhere.
Find out more: How do I clean my fabric mask?
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