The team examined the chances of COVID-19 infection and how the virus is easily passed from person to person. Comparing trends and mitigation procedures in China, Italy, and New York City, the researchers found that using a face mask reduced the number of infections by more than 78,000 in Italy from April 6 to May 9 and by over 66,000 in New York City from April 17 to May 9.

“Wearing a face mask as well as practicing good hand hygiene and social distancing will greatly reduce the chances of anyone contracting the COVID-19 virus.”

“Our results clearly show that airborne transmission via respiratory aerosols represents the dominant route for the spread of COVID-19,” says Renyi Zhang, a professor of atmospheric sciences and a chair in the College of Geosciences at Texas A&M University.

“By analyzing the pandemic trends without face-covering using the statistical method and by projecting the trend, we calculated that over 66,000 infections were prevented by using a face mask in little over a month in New York City. We conclude that wearing a face mask in public corresponds to the most effective means to prevent inter-human transmission.

“This inexpensive practice, in conjunction with social distancing and other procedures, is the most likely opportunity to stop the COVID-19 pandemic. Our work also highlights that sound science is essential in decision-making for the current and future public health pandemics.”

“Our study establishes very clearly that using a face mask is not only useful to prevent infected coughing droplets from reaching uninfected persons, but is also crucial for these uninfected persons to avoid breathing the minute atmospheric particles (aerosols) that infected people emit when talking and that can remain in the atmosphere tens of minutes and can travel tens of feet,” says coauthor Mario Molina, a professor at the University of California, San Diego and a co-recipient of the 1995 Nobel Prize in Chemistry for his role in understanding the threat to the Earth’s ozone layer of human-made halocarbon gases.

Zhang says that many people in China have worn face masks for years, mainly because of the bad air quality of the country.

“So people there are sort of used to this,” he says. “Mandated face-covering helped China in containing the COVID-19 outbreak.”

Zhang says the results should send a clear message to people worldwide: Wearing a face mask is essential in fighting the virus.

“Our work suggests that the failure in containing the propagation of COVID-19 pandemic worldwide is largely attributed to the unrecognized importance of airborne virus transmission,” he says.

“Social distancing and washing our hands must continue, but that’s not sufficient enough protection. Wearing a face mask as well as practicing good hand hygiene and social distancing will greatly reduce the chances of anyone contracting the COVID-19 virus.”

The work appears in PNAS. Additional researchers from the University of Texas at Austin; the University of California, San Diego; and the California Institute of Technology contributed to the work.