There has undoubtedly been a lot of controversy and confusion regarding mask wearing. Much of this confusion is likely due to a lack of concentrated and trusted information regarding pandemic response as well as changes in recommendations from organizations such as the Centers for Disease Control (CDC) and the World Health Organization (WHO). While neither organization originally supported the recommendation of general public mask use, both have changed their tunes. This shouldn't be concerning or a point of contention. Recommendations should be expected shift as evidence builds and we garner a better understanding of all the aspects of this pandemic.
At this point in time both the CDC and WHO along with the majority of health experts agree on the recommendation for mask use by the general public. The evidence is clear that widespread mask wearing can help prevent COVID-19 spread, so mask up!
Why the shift in guidance on wearing masks?
The guidance of the CDC stems from more than just scientific evidence. The original guidance was partially based on what was suspected to be low disease prevalence early in the pandemic. There were also concerns that already limited supplies of personal protective equipment such as surgical masks and N95 respirators would be too rapidly depleted. There was concern that if the general public was also searching for these products our health-care workers would be left in a vulnerable position that would worsen the incidence and spread of disease. While both surgical masks and N95 respirators are tested to meet certain standards cloth masks were an unknown. There was at the time a lack of data showing efficacy of cloth masks in reducing droplet and aerosol spread. As such, they were not immediately recommended for public use as they are now.
Another reason for the shift in guidance is the acknowledgement and prevalence of pre-symptomatic or asymptomatic infection and spread. Masks are not just about protecting the wearer, they are about protecting the community. If you are asymptomatic you likely don't know you're infected and/or infectious. Masks prevent spread of droplets and aerosols from wearers. This is why surgeons wear surgical masks in the operating room. This implies that individuals that don't know that they are sick would be much less likely to accidently infect others simply by wearing a mask in public. It's because of this effect that regular use of masks by 80% of the population is estimated to do more to reduce the spread of COVID-19 than strict lockdown measures.
Additionally, there is a cultural perspective to be considered, particularly in the US. In an interview with reporter Nina Bai, the infectious disease specialist Peter Chin-Hong, MD at UCSF explains that "...Culturally, the US wasn’t really prepared to wear masks, unlike some countries in Asia where the practice is more common... Even now, some Americans are choosing to ignore CDC guidance and local mandates on masks." He goes on to explain that "...The biggest thing with COVID now that shapes all of this guidance on masks is that we can’t tell who’s infected... You can’t look in a crowd and say, oh, that person should wear mask. There’s a lot of asymptomatic infection, so everybody has to wear a mask.”
Current evidence on mask efficacy in COVID-19 prevention
*The following section is an excerpt from a great UCSF article by Nina Bai*
There are several strands of evidence supporting the efficacy of masks.
One category of evidence comes from laboratory studies of respiratory droplets and the ability of various masks to block them. An experiment using high-speed video found that hundreds of droplets ranging from 20 to 500 micrometers were generated when saying a simple phrase, but that nearly all these droplets were blocked when the mouth was covered by a damp washcloth. Another study of people who had influenza or the common cold found that wearing a surgical mask significantly reduced the amount of these respiratory viruses emitted in droplets and aerosols.
But the strongest evidence in favor of masks come from studies of real-world scenarios. The most important thing are the epidemiologic data. Because it would be unethical to assign people to not wear a mask during a pandemic, the epidemiological evidence has come from so-called “experiments of nature.”
A recent study published in Health Affairs, for example, compared the COVID-19 growth rate before and after mask mandates in 15 states and the District of Columbia. It found that mask mandates led to a slowdown in daily COVID-19 growth rate, which became more apparent over time. The first five days after a mandate, the daily growth rate slowed by 0.9 percentage-points compared to the five days prior to the mandate; at three weeks, the daily growth rate had slowed by 2 percentage-points.
Another study looked at coronavirus deaths across 198 countries and found that those with cultural norms or government policies favoring mask-wearing had lower death rates.
Two compelling case reports also suggest that masks can prevent transmission in high-risk scenarios... In one case, a man flew from China to Toronto and subsequently tested positive for COVID-19. He had a dry cough and wore a mask on the flight, and all 25 people closest to him on the flight tested negative for COVID-19. In another case, in late May, two hair stylists in Missouri had close contact with 140 clients while sick with COVID-19. Everyone wore a mask and none of the clients tested positive.
At this point in time both the CDC and WHO along with the majority of health experts agree on the recommendation for mask use by the general public. The evidence is clear that widespread mask wearing can help prevent COVID-19 spread, so mask up!
Why the shift in guidance on wearing masks?
The guidance of the CDC stems from more than just scientific evidence. The original guidance was partially based on what was suspected to be low disease prevalence early in the pandemic. There were also concerns that already limited supplies of personal protective equipment such as surgical masks and N95 respirators would be too rapidly depleted. There was concern that if the general public was also searching for these products our health-care workers would be left in a vulnerable position that would worsen the incidence and spread of disease. While both surgical masks and N95 respirators are tested to meet certain standards cloth masks were an unknown. There was at the time a lack of data showing efficacy of cloth masks in reducing droplet and aerosol spread. As such, they were not immediately recommended for public use as they are now.
Another reason for the shift in guidance is the acknowledgement and prevalence of pre-symptomatic or asymptomatic infection and spread. Masks are not just about protecting the wearer, they are about protecting the community. If you are asymptomatic you likely don't know you're infected and/or infectious. Masks prevent spread of droplets and aerosols from wearers. This is why surgeons wear surgical masks in the operating room. This implies that individuals that don't know that they are sick would be much less likely to accidently infect others simply by wearing a mask in public. It's because of this effect that regular use of masks by 80% of the population is estimated to do more to reduce the spread of COVID-19 than strict lockdown measures.
Additionally, there is a cultural perspective to be considered, particularly in the US. In an interview with reporter Nina Bai, the infectious disease specialist Peter Chin-Hong, MD at UCSF explains that "...Culturally, the US wasn’t really prepared to wear masks, unlike some countries in Asia where the practice is more common... Even now, some Americans are choosing to ignore CDC guidance and local mandates on masks." He goes on to explain that "...The biggest thing with COVID now that shapes all of this guidance on masks is that we can’t tell who’s infected... You can’t look in a crowd and say, oh, that person should wear mask. There’s a lot of asymptomatic infection, so everybody has to wear a mask.”
Current evidence on mask efficacy in COVID-19 prevention
*The following section is an excerpt from a great UCSF article by Nina Bai*
There are several strands of evidence supporting the efficacy of masks.
One category of evidence comes from laboratory studies of respiratory droplets and the ability of various masks to block them. An experiment using high-speed video found that hundreds of droplets ranging from 20 to 500 micrometers were generated when saying a simple phrase, but that nearly all these droplets were blocked when the mouth was covered by a damp washcloth. Another study of people who had influenza or the common cold found that wearing a surgical mask significantly reduced the amount of these respiratory viruses emitted in droplets and aerosols.
But the strongest evidence in favor of masks come from studies of real-world scenarios. The most important thing are the epidemiologic data. Because it would be unethical to assign people to not wear a mask during a pandemic, the epidemiological evidence has come from so-called “experiments of nature.”
A recent study published in Health Affairs, for example, compared the COVID-19 growth rate before and after mask mandates in 15 states and the District of Columbia. It found that mask mandates led to a slowdown in daily COVID-19 growth rate, which became more apparent over time. The first five days after a mandate, the daily growth rate slowed by 0.9 percentage-points compared to the five days prior to the mandate; at three weeks, the daily growth rate had slowed by 2 percentage-points.
Another study looked at coronavirus deaths across 198 countries and found that those with cultural norms or government policies favoring mask-wearing had lower death rates.
Two compelling case reports also suggest that masks can prevent transmission in high-risk scenarios... In one case, a man flew from China to Toronto and subsequently tested positive for COVID-19. He had a dry cough and wore a mask on the flight, and all 25 people closest to him on the flight tested negative for COVID-19. In another case, in late May, two hair stylists in Missouri had close contact with 140 clients while sick with COVID-19. Everyone wore a mask and none of the clients tested positive.
Does the type of mask matter?
N95 respirators are the only masks that when properly used will block the movement of SARS-CoV-2 containing particles completely. These masks are designed to remove particulate matter down to 0.1 microns in diameter. For reference SARS-CoV-2 virions are roughly 0.1 microns in diameter meaning that N95 masks are capable of filtering free virions. N95 masks are really only necessary in medical situations and should be reserved for medical professionals in scenarios such as intubation.
While surgical and cloth masks are not meant to block the movement of particles as small as N95 masks, most virions are transmitted in small respiratory droplets produced from coughing and sneezing. These droplets can vary in size but can be up to ~100 microns in diameter. This is why surgical and cloth masks are still effective in reducing the spread of viral particles.
The concept behind wearing a mask is geared toward risk reduction and not absolute prevention. Focus should be on the wearer preventing spread of their own respiratory droplets rather than preventing the inhalation of respiratory droplets from others. This is also why N95 masks with valves are not recommended. While they will filter and protect the wearer from particulate matter, the valves are designed to release the wearers own respiratory droplets upon exhalation.
At the end of the day anything that covers you nose and mouth will be of some benefit. What is most important to consider for the majority of people is personal comfort. A mask that you can keep on for longer periods of time without discomfort will likely do more for you and those around you than an N95 that you have to repeatedly take off and put back on.
N95 respirators are the only masks that when properly used will block the movement of SARS-CoV-2 containing particles completely. These masks are designed to remove particulate matter down to 0.1 microns in diameter. For reference SARS-CoV-2 virions are roughly 0.1 microns in diameter meaning that N95 masks are capable of filtering free virions. N95 masks are really only necessary in medical situations and should be reserved for medical professionals in scenarios such as intubation.
While surgical and cloth masks are not meant to block the movement of particles as small as N95 masks, most virions are transmitted in small respiratory droplets produced from coughing and sneezing. These droplets can vary in size but can be up to ~100 microns in diameter. This is why surgical and cloth masks are still effective in reducing the spread of viral particles.
The concept behind wearing a mask is geared toward risk reduction and not absolute prevention. Focus should be on the wearer preventing spread of their own respiratory droplets rather than preventing the inhalation of respiratory droplets from others. This is also why N95 masks with valves are not recommended. While they will filter and protect the wearer from particulate matter, the valves are designed to release the wearers own respiratory droplets upon exhalation.
At the end of the day anything that covers you nose and mouth will be of some benefit. What is most important to consider for the majority of people is personal comfort. A mask that you can keep on for longer periods of time without discomfort will likely do more for you and those around you than an N95 that you have to repeatedly take off and put back on.
Sources
1. Still Confused About Masks? Here's the Science Behind How Face Masks Prevent Coronavirus (Bai, UCSF)
2. Reducing Transmission of SARS-CoV-2 (Prather, Wang & Schooley, Science)
3. Respiratory virus shedding in exhaled breath and efficacy of face masks (Leung et al., Nature Medicine)
4. Face Masks Against COVID-19: An Evidence Review (Howard et al., PNAS)
5. Efficacy of masks and face covering in controlling outward aerosol particle emission from expiratory activities (Asadi et al., Nature Scientific Reports)
6. Science Forum: SARS-CoV-2 (COVID-19) by the numbers (Bar-On et al., eLife)
2. Reducing Transmission of SARS-CoV-2 (Prather, Wang & Schooley, Science)
3. Respiratory virus shedding in exhaled breath and efficacy of face masks (Leung et al., Nature Medicine)
4. Face Masks Against COVID-19: An Evidence Review (Howard et al., PNAS)
5. Efficacy of masks and face covering in controlling outward aerosol particle emission from expiratory activities (Asadi et al., Nature Scientific Reports)
6. Science Forum: SARS-CoV-2 (COVID-19) by the numbers (Bar-On et al., eLife)
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