Graphics shared thousands of times on social media claim to show the exact probability of COVID-19 carriers spreading the disease if they or another person wears a mask. The claim is misleading; experts say that while masks do decrease the risk, there is no reliable information on the specific chance of transmission.
The graphics show a "COVID-19 Carrier" in three different scenarios, saying that if the carrier does not wear a mask and a nearby person does, the risk of contagion is 70 percent.
If the carrier wears a mask and a nearby person does not, the risk is five percent, and if both the carrier and the nearby person wear a mask, the risk is 1.5 percent, they say.
Some graphics also include the message "WEAR IT."
Posts making the claim have been shared on Facebook here, here and here, on Instagram here and here, and on Twitter here.
Dr. Shelley Payne, director of the LaMontagne Center for Infectious Disease at the University of Texas at Austin, explained that while the relative order of risk shown in the graphic is correct, "the actual numbers will depend on a number of factors, including amount of virus shed by the case or carrier, distance between the two individuals, type of mask material, fit of the mask."
Too many variables and a lack of experimental data -- except in hospital settings with standardized masks -- make the risk of contagion hard to calculate, Payne told AFP by email.
"I don't think there are reliable numbers on how much protection a face mask provides," she said.
But "the probability of spread is highest if the carrier or case is not wearing a mask and lowest if both the carrier and contact are masked," Payne said.
"Not all masks are created equal," said Dr. Brendan Brown, associate professor at the University of California, Riverside School of Medicine.
"We don't know the transmission percentages and protection provided for against COVID-19 for any specific mask, but we do know that N95 is the gold standard," Brown said in an email, referring to masks that the US Centers for Disease Control and Prevention says are "critical supplies" that should be reserved for health care workers.
The CDC recommends that the general public use cloth masks to slow the spread of the novel coronavirus, which has killed more than 230,000 people worldwide.
Dr. John Criscione, professor of biomedical engineering at Texas A&M University, researched solutions for mask shortages by testing common household items such as air filters, pillow cases, shower curtains and vacuum bags.
While the graphics shared on social media may not provide an accurate assessment of the exact risk, the point rings true that COVID-19 carriers should wear a mask, Criscione says: "Any covering is better than no covering at all."