GREENSBORO, N.C. — A chart comparing mask effectiveness across the different types has gained traction on social. According to the doctor who made it, people may be misinterpreting it.
“I worry a lot about people taking the numbers and seeing them as sort of a bright line between when you’re safe and when you’re not safe,” Dr. Lisa Brosseau, a retired professor in the University of Illinois Chicago’s school of public health, said.
Brosseau developed the chart for American Conference for Governmental Industrial Hygienists, a nonprofit organization.
The chart breaks down how long it would take to become exposed to an infectious dose of COVID-19 based on various scenarios. According to Brosseau, it would take 15 minutes for an unmasked person to expose another unmasked to enough COVID-19 to infect them. If the infected person is wearing a surgical mask, that time frame doubles.
However, the data need context. The chart was published in spring 2021, prior to the emergence of the delta and omicron variants. Doctors say both of the variants are more contagious than the original strain of COVID-19. That could skew the data.
“The numbers that are presented in that table are presented in a very concrete way,” Dr. Emily Sickbert-Bennett, an associate professor of infectious diseases at the University of North Carolina School of Medicine, said. “And this is a very abstract concept."
“There’s a lot of things that go into exposure that could make it a much shorter time to an infectious dose,” Brosseau said. “Those things are really hard to know what their effects will be, and they’re hard to measure."
Even if Brosseau updated her chart to account for each of the more infectious strains, she doesn't think she would change that 15-minue time window.
"I tell people I’m really not in favor of changing that 15-minute contact-tracing time to anything else even if we know that omicron is more transmissible because I don’t know what to change it to,” Brosseau said.