Not all COVID masks are equally effective in advancing public health goals, and in recent days a growing number of companies that require face coverings have advised their employees and customers to avoid those with vents.
The published policies of three major airlines -- United, JetBlue, and Delta -- now state that face coverings with an exhale vent are not adequate. Walt Disney World did so last week.
"I think it's about evolving the program as we've learned more," said Matt Miller, United Airlines VP for Airport Operations at three western hubs.
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"Masks with exhalation valves or vents" are specifically mentioned as not recommended on the "About Masks" web page that the Centers for Disease Control and Prevention updated Wednesday, consistent with its earlier advice.
Such masks are indeed professional grade and designed to protect the wearer against exposure to fumes, chemical or dust. But they are not intended to filter the wearer's exhaled breath.
"When you have a valve in that mask with a valve, it allows you to exhale, and allows you to exhale particles of the virus, which can then be spread to others," said Anne Rimoin, PhD, MPH, a UCLA professor of epidemiology and director of the Center for Global and Immigrant Health. "So when you're looking for a mask, you need a mask that does not have an exhalation valve."
Though there is evidence face covering provides a protective barrier for the wearer as well, the focus of public health orders remains protecting others.
"Masks with one way valves are not really helpful in that way," said Muntu Davis, MD, the public health officer for Los Angeles County. "The one way valve ... is not something we allow."
They can also be more costly than a simple cloth mask, but they do have an allure. Because humid exhaled breath can dissipate more quickly from vented masks, they feel cooler and drier to the wearer than unvented fabric, and that is a temptation.
"When you have a mask that has a valve in it, it might make it more comfortable for you, but the problem is that it defeats the purpose of preventing the spread to other people," said Dr. Rimoin. "We're all in this together."
She noted that unvented cloth masks remain one of the most effective tools against COVID-19 spread, even more so in light of new evidence from a newly released South Korean study. It found that up to 30 percent of those infected with COVID never develop symptoms, but still can carry high levels of the contagious virus.
Upgrading mask guidelines is only the latest step that United Airlines has taken with partners in an effort to offer more customers and employees more protection against COVID-19 spread, said Miller. He cited "United CleanPlus," a collaboration with the Cleveland Clinic and the disinfectant maker Clorox for adding protective infrastructure and sanitizing airliner cabins, terminal areas, and other possible exposure points.
"Every step we take, we really do feel it is strengthening our position to really be able to be provide the safest and most protected environment that we can through the travel experience," Miller said.
And if you forget your mask, or bring one with a vent, Miller said not to worry. United keeps available a supply of complimentary disposable masks.