Study finds most respiratory viruses are airborne, so are masks here to stay? ‘Not really,’ UCSD expert says

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A new research study co-led by an atmospheric chemist at UC San Diego’s Scripps Institution of Oceanography in La Jolla has determined that most respiratory viruses, not just the coronavirus that causes COVID-19, all can spread via the air.

“We’ve been living with poor air quality,” said professor Kimberly Prather, who also is director of the National Science Foundation Center for Aerosol Impacts on Chemistry of the Environment.

“Masks obviously will protect you against a wider range of respiratory viruses,” Prather said.

But when asked whether the study implies that masks should be a permanent fixture in people’s lives, she said, “Not really.”

Prather said she hopes the study will “raise awareness of how poorly ventilated schools — businesses, too — have been for a very long time.” Upgrading ventilation and air filtration indoors not only will decrease the transmission of respiratory viruses, but also indoor air pollution, she said.

“Especially in schools, we’ve just [come] to accept the kids got sick,” Prather added. “When you had kids in school, you spent your winters sick, and it doesn’t have to be that way. If we invest in our schools, that’s going to reap health benefits for a long, long time.”

The study, being published Friday, Aug. 27, in Science magazine, was led by Prather and Chia Wang, director of the Aerosol Science Research Center and an aerosol physical chemist at National Sun Yat-sen University in Taiwan. It found airborne transmission to be the leading pathway for transmission of most respiratory diseases, not just COVID-19.

In October, Prather and five other scientists wrote a letter urging researchers of the SARS-CoV-2 coronavirus to shift their attention “to protecting against airborne transmission” rather than on the wide belief that the most likely transmission route was surface contact or contact with large droplets produced by coughs and sneezes.

On Aug. 26, the San Diego Unified School District, which operates five public schools in La Jolla, sent an email to parents updating its mask policy for the coming school year to require masks outdoors on campuses as well as indoors.

State rules currently require only indoor masking. SDUSD says its new policy is meant to keep kids safe and in school.

The email said students can remove their masks outdoors during “mask breaks.” “During these breaks, students should maintain six feet distance from each other. … Masks may be removed outdoors in certain situations and with certain distancing recommendations during physical education, athletics and performing arts programs,” as well as when students are eating.

Prather, who has advised the district since last year on its pandemic-related safety protocols, said the update was made as “there are reports that [the highly contagious] Delta variant is being transmitted outdoors.”

Prather said the new study found that respiratory aerosols, formed by exhalation in breathing, talking, singing, shouting, coughing and sneezing, remain suspended in still air for more than five seconds and can travel from an infected person and be inhaled.

“The way this [coronavirus] snuck its way around the globe — it’s done it silently — [is] because over half of the spread is from people who don’t even know they’re sick,” Prather said. “They’re just breathing and talking.”

Referring to the common belief that the pandemic will slow if people maintain six feet among them, Prather said: “If six feet was enough, we wouldn’t be in the middle of a pandemic. If it really was just droplets falling to the ground … that does not explain it.”

“I was the one that explained it to Dr. [Anthony] Fauci that [the virus] goes a lot farther than six feet,” Prather said. “It’s a paradigm shift for the field.”

The study team looked at other viruses while researching the spread of SARS-CoV-2. In reviewing several studies of superspreading events during the pandemic, researchers determined that aerosols are the most likely transmission route rather than surface contacts or contact with large droplets.

Plexiglass barriers — which protect against droplet exposure and have been erected in many schools and businesses to try to slow the pandemic — could actually impede ventilation, Prather said, as the barriers can trap aerosols.

“What you’d like is the air to be freely flowing across the room so you can bring in fresh air,” Prather said.

Prather said she was part of a recent forum to explain further protocols to keep children safer in schools. It can be viewed at