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  • Writer's pictureP.K. Peterson

Masks and COVID-19: The Devil is in the Detail

"Let the dataset change your mindset."

- Hans Rosling

“Wear the most protective mask you can that fits well and that you will wear consistently.”

- U.S. Center for Disease Control and Prevention, January 14, 2022

We are in the midst of a blistering surge of SARS-CoV-2 infections caused by the Omicron variant. It is now clear that vaccines alone are not sufficient in controlling the spread of this virus and that wearing a mask is essential. In this Germ Gems post, I focus on what kinds of masks work best and how to use them.

History of masks in preventing infectious diseases. Pioneered by surgeons, the practice of using face masks to prevent infectious diseases is almost as old as the origin of the “germ theory of disease” in the late 19th century. The Chinese-Malaysian epidemiologist Dr. Wu Lien introduced the use of face masks in the community to control the 1910 pneumonic plague outbreak in Manchuria. He identified the cloth mask as “the principal means of personal protection.” From that time forward, masks have continued to be used in communities throughout East Asia to control the transmission of respiratory infections. Until the COVID-19 pandemic hit, widespread mask usage in the community was not practiced by the rest of the world.

In my 40 plus years of practice as an infectious disease specialist I wore a mask only in two clinical settings, when consulting on patients with pulmonary tuberculosis or influenza—both are airborne infections.

Why masks are so important in the war against SARS-CoV-2. In the first year of the COVID-19 pandemic scientists determined that SARS-CoV-2 is an airborne pathogen that is transmitted via tiny aerosols generated by coughing, sneezing, singing, or talking. To prevent viral particles from gaining access to the airway (upper and lower respiratory tract), masks made with material with an electrostatic charge, also known as respirators, have been found to block viral entry most effectively. Wearing respirators with a snug fit­­—no gaps around the nose, cheeks or chin—is crucial.

Why N95 or equivalent respirators are best. Two decades ago, scientists who study the role of particulate matter (PM) in air pollution showed that inhalation of particles <2.5 micrometers (PM2.5) can reach the lungs and that masks that filter out PM2.5 help prevent the myriad of diseases associated with air pollution. Last year, researchers found that SARS-CoV-2, the wily pathogen that causes COVID-19, can hitch a ride on PM2.5 thereby providing a link between air pollution and COVID-19. They also found that the respirators (masks) that filter out PM2.5 were best at protecting against SARS-CoV-2.

The National Institute of Occupational Safety & Health (NIOSH) rates respirators. Respirators that filter out 95 percent of airborne particles are given a 95 rating. N95 respirators filter out 95% of airborne particles using two filtration methods, mechanical filtering by the mask fibers and filtering by electrostatic charge. Respirators that filter out at least 99% of airborne particles have a 99 rating. Masks that filter out 99.97 percent of airborne particles, considered to be essentially 100% by the NIOSH, receive a 100 rating.

Why we need to wear these respirators. According to a study published recently in the Proceedings of the National Academy of Sciences, fitted particle-filtering respirators like N95s are more effective at preventing infection with SARS-CoV-2 than either non-fit tested respirators or surgical masks. To help assure a tight fit to the face, a N95 respirator with a metal nose clip and head straps instead of ear loops is recommended.

It has been shown that N95 masks can be safely reused after decontamination using either a vaporized hydrogen peroxide process—a method of decontamination more suited for hospitals than homes—or, as the virus loses its pathogenicity, through a process of rotating masks. An article in the January 14, 2022 issue of the Smithsonian Magazine entitledCan You Reuse a KN or N95 Mask? Experts Say Yes, but Follow These Steps” provides guidance on reusing and rotating N95 or KN95 masks. The experts quoted in this article suggest having multiple masks in rotation giving each mask a sanitation break between uses by putting the mask in a brown paper bag for 24 to 48 hours before using it again.

Ideally, however, N95 respirators should only be used once and discarded as they lose their electrostatic charge. See

In addition to N95 respirators, KN95, KF94, and FFP respirators are highly protective. The main difference between N95 and KN95 masks is that N95s are the standard in the U.S. while KN95s are the standard in China. (A word of caution regarding some KN95 masks marketed as “Certified KN95 mask adopted by the CDC.” The Centers for Disease Control and Prevention (CDC) has said 60% of KN95 masks in the U.S. are fake, and on January 11, 2022, the agency provided a notice about how to identify NIOSH-approved respirators, “Counterfeit Respirators/Misrepresentation of NIOSH-Approval.”)

The rampant spread of Omicron demands taking masks more seriously. On January 14, 2022, the CDC clarified its position on wearing masks as a tool in the prevention of SARS-Cov-2 prevention and recommended wearing respirators such as N95 or KN95. But as CDC director Rochelle Walensky remarked recently, “[T]he best mask that you wear is the one you will wear and the one you can keep on all day long and tolerate in public indoor settings.”

Nonetheless, the data show that these higher-quality respirators such as N95 or KN95 provide better protection than either surgical or cloth masks. Moreover, these masks are readily available and not that expensive. For more information on masks go to

We all know that universal masking is not going to happen overnight. Each one of us, however, needs to do our part and WEAR A MASK. It is still one of the best ways to protect oneself and others against infection.

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

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