Atlanta—The use of cloth face masks to help prevent transmission of COVID-19 is controversial and highly politicized.
In an effort to inject some data into the discussions, the CDC recently released a scientific brief on the issue.
The CDC points out that SARS-CoV-2 infection is transmitted predominately by respiratory droplets generated by coughing, sneezing, singing, talking, or breathing. That’s why public-health officials recommend community use of nonvalved multilayer cloth masks to prevent transmission.
“Masks are primarily intended to reduce the emission of virus-laden droplets (“source control”), which is especially relevant for asymptomatic or presymptomatic infected wearers who feel well and may be unaware of their infectiousness to others, and who are estimated to account for more than 50% of transmissions,” according to the brief. “Masks also help reduce inhalation of these droplets by the wearer (“filtration for personal protection”).”
Early evidence suggested that the primary benefit was in preventing transmission by the wearer. Now, research also has suggested a benefit for wearing a mask to keep from contracting the virus. “The community benefit of masking for SARS-CoV-2 control is due to the combination of these effects; individual prevention benefit increases with increasing numbers of people using masks consistently and correctly,” the CDC states.
The research brief also discusses a range of methods by which cloth masks help protect wearers and others. It notes that multilayer cloth masks block release of exhaled respiratory particles into the environment, as well as the microorganisms those particles carry.
“Cloth masks not only effectively block most large droplets (i.e., 20-30 microns and larger) but they can also block the exhalation of fine droplets and particles (also often referred to as aerosols) smaller than 10 microns, which increase in number with the volume of speech, and specific types of phonation. Multi-layer cloth masks can both block up to 50-70% of these fine droplets and particles and limit the forward spread of those that are not captured,” according to the report.
In fact, the CDC emphasizes that as much as 80% blockage has been achieved in human experiments that have measured blocking of all respiratory droplets with cloth masks; in some studies, the cloth masks recommended for the public have performed as well as surgical masks as barriers for source control.
The new research brief also explains how cloth-mask materials can reduce wearers’ exposure to infectious droplets through filtration, including filtration of fine droplets and particles less than 10 microns. Mask types have varied widely across studies, according to the CDC, which verifies that multiple layers of cloth with higher thread counts have demonstrated superior performance compared to single layers of cloth with lower thread counts, in some cases filtering nearly 50% of fine particles less than 1 micron.
It also describes how some materials, such as polypropylene, enhance filtering effectiveness by generating a triboelectric charge that enhances capture of charged particles and that others, such as silk, help repel moist droplets and reduce fabric wetting, which maintains breathability and comfort.
The brief lists information about a range of studies—including seven that confirmed the benefit of universal masking in community-level analyses—to bolster evidence of “real-world” effectiveness.
“Experimental and epidemiological data support community masking to reduce the spread of SARS-CoV-2,” the article concludes. “The prevention benefit of masking is derived from the combination of source control and personal protection for the mask wearer. The relationship between source control and personal protection is likely complementary and possibly synergistic, so that individual benefit increases with increasing community mask use.”
The CDC calls for further research to expand the evidence base for the protective effect of cloth masks and especially to pinpoint the combinations of materials that maximize both their blocking and filtering effectiveness, as well as fit, comfort, durability, and consumer appeal. It adds, “Adopting universal masking policies can help avert future lockdowns, especially if combined with other non-pharmaceutical interventions such as social distancing, hand hygiene, and adequate ventilation.”
The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.
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