Why face masks are so important

UNC study confirms importance of face masks

June 12, 2020 

Conflicting health advice from officials

Remember back in January and February, as the Covid-19 pandemic spread across the country, how everybody believed non-surgical grade face coverings did little to help battle the virus? That changed in early April, when the Centers for Disease Control and Prevention announced simple, homemade cloth face coverings such as masks and even bandanas could help slow the unintended spread of the coronavirus to others. By then, researchers had discovered that the virus spread through water droplets emitted when coughing, sneezing, and even unintentionally launched saliva (through speaking).

Researchers also found that people infected with COVID-19 might show mild symptoms or none at all. So, it made sense that using a cloth face covering when around others could help block those saliva particles and slow the spread of transmission to others, especially if you don't know you're sick.

Research documents specific ways face masks help

Now, scientists at the UNC School of Medicine and the UNC Gillings School of Global Public Health have characterized the specific ways in which SARS-CoV-2 – the coronavirus that causes COVID-19 – infects the nasal cavity and the lungs. And yes, face coverings can prevent it. The study was published in the journal Cell.

The findings suggest the virus tends to become firmly established first in the nasal cavity. But while the nasal cavity is the primary infection point, the virus can be drawn into the lungs, where it may cause more serious disease, including pneumonia.

“If the nose is the dominant initial site from which lung infections are seeded, then the widespread use of masks to protect the nasal passages, as well as any therapeutic strategies that reduce virus in the nose, such as nasal irrigation or antiviral nasal sprays, could be beneficial,” said study co-senior author Richard Boucher, MD, director of the Marsico Lung Institute at the UNC School of Medicine.

In one set of experiments, researchers looked at how efficiently the SARS-CoV-2 coronavirus infected different parts of the human airway. They found high infectivity in cells lining the nasal passages, less infectivity in the cells lining the throat and bronchia, and low infectivity in lung cells. That same test discovered that ACE2 – the cell surface receptor that the virus uses to get into cells – was more abundant on nasal-lining cells and less abundant on the surface of lower airway cells. Scientists say that might explain why upper airway nasal-lining cells were more susceptible to infection.

Researchers also found that the virus can infect airway-lining cells called epithelial cells, and to a limited extent the all-important “pneumocyte” lung cells that help transfer inhaled oxygen into the bloodstream.

Still, big questions remain. The study also looked at two enzymes found on human cells. It’s thought that SARS-CoV-2 uses the two enzymes to re-shape key virus proteins and enter human cells. The more abundant the enzymes, the more infections. But while the virus infected cells in the nasal cavity, it did not infect cells in the lower airways, even though the enzymes were present. That means there is some other factor that determines which cells are infected.

While that factor is still a mystery, researchers believe they have answered many questions. “This is a landmark study that reveals new and unexpected insights into the mechanisms that regulate disease progression and severity following SARS-CoV-2 infection,” explains Ralph Baric, PhD, the William R. Kenan Distinguished Professor of Epidemiology at the UNC Gillings School of Public Health. “This will support national vaccine efforts designed to control the spread and severity of this terrible disease.”

—Frank Graff

Frank Graff is a producer/reporter with UNC-TV, focusing on Sci NC, a broadcast and online science series.