As the Centers for Disease Control and Prevention (CDC) are changing tack regarding their recommendation to the public about wearing face masks, some experts explain how certain masks could help keep the coronavirus at bay. However, these should be our last resort, they warn.
A few days ago, the CDC issued new guidance on the circumstances under which it is advisable to wear masks during the COVID-19 pandemic.
The federal agency now “recommends wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain (e.g., grocery stores and pharmacies) especially [original emphasis] in areas of significant community-based transmission.”
Yet, by advising the use of homemade cloth masks, the CDC are upholding their earlier recommendation that people refrain from purchasing surgical masks and N95 respirators, which they deem to be “critical supplies” for healthcare workers, who face shortages of protective equipment.
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A newly published study from the University of Maryland, College Park and The University of Hong Kong now shows how surgical masks, in particular, could help prevent people with a viral infection from shedding infectious particles.
The researchers started their study before the new coronavirus pandemic, so their investigation does not include people who contracted SARS-CoV-2.
Nevertheless, their findings may be relevant to current international debates about the efficacy of masks in preventing the spread of SARS-CoV-2.
The researchers’ findings appear in the journal Nature.
Surgical masks can prevent transmission
In the study, the team worked with 246 participants who had acquired a respiratory infection from a flu virus, a coronavirus, or a rhinovirus.
The researchers split the participants into two groups, providing some with surgical masks and leaving others without.
Then, they asked everyone to exhale through an innovative machine designed to capture particles emitted through exhalation — a device suggestively named Gesundheit II — to determine whether the masks could effectively catch the tiny droplets that carry these viruses.
This idea for the test arose in the wake of a previous study, spearheaded by Prof. Donald K. Milton. The study also used the Gesundheit II machine, and the results indicated that a person with the flu could shed infectious particles without coughing or sneezing.
Even minuscule droplets carried by regular breathing were able to spread the flu virus, that study demonstrated.
In the current investigation, the team found that surgical masks could help reduce the amount of coronavirus shed by participants — and suggested that simply breathing could spread this type of virus.
Masks also helped reduce the amount of flu virus shed through coughing or sneezing, but not through aerosols emitted by just breathing.
“In 111 people infected by either coronavirus, influenza virus, or rhinovirus, masks reduced detectable virus in respiratory droplets and aerosols for seasonal coronaviruses, and in respiratory droplets for influenza virus,” says the study’s first author, Nancy H. L. Leung, Ph.D., who had conducted the research for her doctoral dissertation.
“In contrast,” she went on to note, “masks did not reduce the emission of rhinoviruses.”
Based on the current findings, co-senior author Prof. Benjamin J. Cowling — also the co-director of the World Health Organization (WHO) Collaborating Centre for Infectious Disease Epidemiology and Control — notes that surgical masks could play a role in fighting the COVID-19 pandemic.
“The ability of surgical masks to reduce seasonal coronavirus in respiratory droplets and aerosols implies that such masks can contribute to slowing the spread of COVID-19 when worn by infected people,” says Prof. Cowling.
However, the researchers emphasize that for members of the public, masks should be the very last protective measure in the context of the current pandemic.
“Personal protective equipment like N95 masks are not our first line of defense. They are our last, desperate thing that we do.”
– Co-senior author Prof. Donald K. Milton
Instead, a more useful first-line measure for protecting the public may be to install more appropriate ventilation in public spaces such as supermarkets, Prof. Milton notes.
It may also be helpful, he explains, to install UVC lighting by ceiling fans, a method that may kill some viral particles and bacteria that are sucked through the fans.
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