CDC asks Americans to wear cloth face masks, but there's little proof they can protect you from coronavirus
The US Centers for Disease Control and Prevention (CDC) has now recommended that all Americans should wear cloth face coverings when they have to go out in public where other social distancing measures are difficult to maintain. This includes places such as grocery stores and pharmacies, especially in areas of significant community-based transmission.
The reason: CDC says that a significant portion of individuals with coronavirus lack symptoms (asymptomatic) and even those who eventually develop symptoms (pre-symptomatic) can transmit the virus to others before showing symptoms. “This means that the virus can spread between people interacting in close proximity -- for example, speaking, coughing, or sneezing -- even if those people are not exhibiting symptoms. In light of this new evidence, CDC recommends wearing cloth face masks in public settings,” says the CDC.
“Such a measure could slow the spread of the virus and help people who may have the virus and do not know it from transmitting it to others,” say experts.
Supplies of medical-grade masks are running critically low in many places hard hit by the new coronavirus. Accordingly, the CDC emphasizes that cloth face coverings being advised are not surgical masks or N-95 respirators. “Those are critical supplies that must continue to be reserved for healthcare workers and other medical first responders, as recommended by current CDC guidance,” it says. The agency also reiterates that it is critical to maintain a distance of 6-feet from another person and that the face cover is not a substitute for social distancing.
The CDC explains cloth face coverings fashioned from household items or made at home from common materials at low cost can be used as an additional, voluntary public health measure. There is also a video on the CDC website in which US Surgeon General Dr Jerome Adams demonstrates how people can make their own face covering with items one can find around the house such as an old scarf, a bandana, a hand towel or even an old t-shirt.
Previous CDC guidelines had said that if a person is not sick, they do not need to wear a facemask unless they are caring for someone who is sick (and they are not able to wear a facemask).
In February, the US Surgeon General had also tweeted, “Seriously people- STOP BUYING MASKS! They are NOT effective in preventing general public from catching #Coronavirus, but if healthcare providers can’t get them to care for sick patients, it puts them and our communities at risk!”
But can cloth masks protect you?
Current evidence is scant and mixed. Generally, research suggests surgical masks and N95 respirators are significantly more effective at preventing the spread of viral particles than cloth.
According to a commentary, given the paucity of information about their performance as source control in real-world settings, along with the extremely low efficiency of cloth masks as filters and their poor fit, there is no evidence to support their use by the public or healthcare workers to control the emission of particles from the wearer.
Their use may also give a false sense of security. If masks had been the solution in Asia, shouldn't they have stopped the pandemic before it spread elsewhere, question experts. Based on a review of relevant studies, the experts suggest that cloth masks will be ineffective at preventing SARS-CoV-2 transmission, whether worn as source control or as personal protective equipment.
“We do not recommend requiring the general public who do not have symptoms of COVID-19-like illness to routinely wear cloth or surgical masks because there is no scientific evidence they are effective in reducing the risk of SARS-CoV-2 transmission. Their use may result in those wearing the masks to relax other distancing efforts because they have a sense of protection. We need to preserve the supply of surgical masks for at-risk healthcare workers,” say experts in the commentary published by the Center for Infectious Disease Research and Policy (CIDRAP), University of Minnesota.
The experts say that sweeping mask recommendations, as proposed by many, will not reduce SARS-CoV-2 transmission, as evidenced by the widespread practice of wearing such masks in Hubei province, China, before and during its mass COVID-19 transmission experience earlier this year.
Following a recommendation that cloth masks be explored for use in healthcare settings during the next influenza pandemic, the National Institute for Occupational Safety and Health (NIOSH) conducted a study of the filter performance on clothing materials and articles, including commercial cloth masks marketed for air pollution and allergens, sweatshirts, t-shirts, and scarfs. “All of the cloth masks and materials had near-zero efficiency at 0.3 µm, a particle size that easily penetrates into the lungs. Another study evaluated 44 masks, respirators, and other materials with similar methods and small aerosols (0.08 and 0.22 µm). N95 filter efficiency was greater than 95%. Medical masks exhibited 55% efficiency, general masks 38% and handkerchiefs 2% (one layer) to 13% (four layers),” say the experts.
According to the researchers, such studies demonstrate that cloth or homemade masks will have very low filter efficiency (2% to 38%). Medical masks are made from a wide range of materials, and studies have found a wide range of filter efficiency (2% to 98%), with most exhibiting 30% to 50% efficiency, they add.
The commentary says a randomized trial comparing the effect of medical and cloth masks on healthcare worker illness found that those wearing cloth masks were 13 times more likely to experience influenza-like illness than those wearing medical masks.
“In sum, very poor filter and fit performance of cloth masks described earlier and very low effectiveness for cloth masks in healthcare settings lead us to conclude that cloth masks offer no protection for healthcare workers inhaling infectious particles near an infected or confirmed patient,” researchers conclude.
Many other studies discourage their use. A 2015 analysis shows that laboratory-confirmed viruses were significantly higher in the cloth masks group compared with the medical masks group. The study found that cloth mask wearers had higher rates of infection than even the standard practice control group of health workers, and the filtration provided by cloth masks was poor compared to surgical masks. The penetration of cloth masks by particles was almost 97% and medical masks 44%.
The authors of the 2015 study made a statement recently regarding their study findings in the context of COVID-19. Stating that some health workers may still choose to work in the absence of adequate personal protective equipment, and in such cases, the physical barrier provided by a cloth mask may give some protection, but likely much less than a surgical mask or a respirator.
“Health workers are asking us if they should wear no mask at all if cloth masks are the only option. Our research does not condone health workers working unprotected. We recommend that health workers should not work during the COVID-19 pandemic without respiratory protection as a matter of work health and safety,” says the statement. They add, “For COVID-19, wearing a mask is not enough to protect healthcare workers – use of gloves and goggles are also required as a minimum, as SARS-CoV-2 may infect not only through the respiratory route but also through contact with contaminated surfaces and self-contamination.”
In a separate study, researchers recommend that a homemade mask should only be considered “as a last resort” to prevent droplet transmission from infected individuals, but it would be better than no protection.
Another study also says that any type of general mask use is likely to decrease viral exposure and infection risk on a population level, despite imperfect fit and imperfect adherence, personal respirators providing most protection. “Masks worn by patients may not offer as great a degree of protection against aerosol transmission,” says the study. The researchers emphasize that it is also critical not to focus on a single intervention in case of a pandemic, but to integrate all effective interventions for optimal protection.
In the absence of consensus, experts advise people to follow hand hygiene and social distancing to prevent disease spread. They emphasize cloth masks are not a substitute for either.
Evidence for surgical masks
Researchers at the WHO Collaborating Center for Infectious Disease Epidemiology and Control at The University of Hong Kong, Hong Kong hospitals, and Harvard University studied the impact of surgical masks on the transmission of respiratory viruses, including coronaviruses when used by symptomatic individuals.
The study, published in Nature Medicine on April 3, found that surgical masks reduced the emission of droplets and aerosols exhaled by symptomatic patients. The masks resulted in a significant reduction in coronavirus detected in aerosols and a “trend toward reduced detection” for respiratory droplets -- that is, observed reduction, but not statistically significant. Conversely, the study found a significant reduction in influenza detected in respiratory droplets, but no significant reduction for aerosols.
The coronavirus in this study was a “seasonal” coronavirus, as opposed to SARS-CoV-2, but it provides support for guidance that encourages symptomatic individuals to wear masks to reduce transmission. “Our results indicate that surgical face masks could prevent transmission of human coronaviruses and influenza viruses from symptomatic individuals,” says the research team.