“Cloth masks are not going to cut it with omicron,” says Linsey Marr, a researcher at Virginia Tech who studies how viruses transmit in the air.

Omicron is so much more transmissible than coronavirus variants that have come before it. It spreads at least three times faster than delta. One person is infecting at least three others at a time on average, based on data from other countries.

“It’s very contagious,” says Dr. Robert Wachter, chair of the Department of Medicine at the University of California, San Francisco. “And the kind of encounter that you could have had with prior versions of the virus that would have left you uninfected, there’s now a good chance you will get infected from it.”

True, a cloth mask can be a “marginally OK to maybe a decent filter,” Marr says. But with something as highly transmissible as omicron, just “OK” isn’t good enough.