- The CDC published new coronavirus guidelines on face masks, clarifying that face covers can help both the wearer and other people nearby.
- In previous face mask guidelines, the CDC only said that masks prevent an infected person from spreading the virus to others.
- The agency cites several studies that have shown the effectiveness of face masks at reducing the risk of contracting COVID-19.
Face masks remain a controversial coronavirus topic, as many people continue to resist using a simple device that can reduce the risk of COVID-19 transmission. The use of face coverings became a political topic from the moment the CDC started advising people to wear face masks in public. That happened in early April, at a time when the US was battling a PPE shortage in hospitals. Since then, masks remained a divisive topic despite all the evidence that shows they can block pathogens like the novel coronavirus and reduce the spread. No face mask can provide 100% protection, but high-quality face masks like N95 masks and KN95 masks have at least 95% efficacy. Studies have also shown that the higher the percentage of people wearing masks, the lower the number of COVID-19 deaths. Data from the southern hemisphere also showed that face masks and social distancing stopped the usual flu epidemics, since people were observing COVID-19 safety measures.
The physical barrier that face masks provide can capture droplets of all sizes and prevent the coronavirus and other viruses from reaching the mouth and nose. Masks protect protection to both the wearer and everyone around them from inhaling aerosols and droplets. But the CDC has only just now updated its guidelines to acknowledge that the person wearing the mask is also protected.
The previous CDC guidance on masks said the main benefit of mask-wearing was to prevent infected people from spreading the virus to others. But the CDC updated its guidelines this week with wording that makes it clear that face masks also protect the wearer:
ARS-CoV-2 infection is transmitted predominately by respiratory droplets generated when people cough, sneeze, sing, talk, or breathe. CDC recommends community use of masks, specifically non-valved multi-layer cloth masks, to prevent transmission of SARS-CoV-2. 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. Masks also help reduce inhalation of these droplets by the wearer (“filtration for personal protection”). 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 guidelines cite several studies to support the finding that “cloth mask materials can also reduce wearers’ exposure to infectious droplets through filtration, including filtration of fine droplets and particles less than 10 microns.” The CDC references a recent high-exposure event that involved two infected hair stylists who wore masks while interacting for an average of 15 minutes with 139 clients who were also wearing masks. None of the 67 clients who agreed to interviews were infected. Anecdotal coverage of the event has suggested that none of the other 72 clients were infected either.
A different study from Thailand showed that people who reported having always worn a mask during high-exposure events experienced a greater than 70% reduced risk of infection. The CDC also references the COVID-19 outbreak aboard the USS Theodore Roosevelt, which showed that the use of face coverings on-board was associated with a 70% reduced risk of infection. Scientists who investigated COVID-19 transmission on flights longer than 10 hours found that face masks prevented in-flight transmission. The CDC also notes that an economic analysis found that increasing universal mask-wearing by 15% could prevent lockdowns and reduce losses by up to $1 trillion.
The agency’s conclusion isn’t surprising. Wearing masks helps everyone involved in adhering to this measure that can help authorities control outbreaks:
Experimental and epidemiological data support community masking to reduce the spread of SARS-CoV-2. 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 synergistic14, so that individual benefit increases with increasing community mask use. Further research is needed to expand the evidence base for the protective effect of cloth masks and in particular to identify the combinations of materials that maximize both their blocking and filtering effectiveness, as well as fit, comfort, durability, and consumer appeal. 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.
Public health experts have been advising the same safety measures for months, emphasizing face mask use in public settings.