"So you're saying this mask I've been wearing for a year isn't really protecting me very much?" Wallace asked.
"You probably need to upgrade your mask, Chris," Jha told him.
CHRIS WALLACE, FOX NEWS: I read a report, actually several reports this week, that cloth masks, which, frankly, are the kinds of masks I usually wear, are not really effective. Is that true?
DR. ASHISH JHA, DEAN, BROWN UNIVERSITY SCHOOL OF PUBLIC HEALTH: Yes, cloth masks, unto themselves, generally not effective. That's why I think surgical masks are better. There are, of course, higher-quality masks. Cloth masks may be ten or 20 percent effective, not great against the delta variant.
WALLACE: So you're saying this mask I've been wearing for a year isn't really protecting me very much?
JHA: I'm saying that given the delta variant that's out there, you probably need to upgrade your mask, Chris.
WALLACE: Well, thank you for that and I think a lot of people thank you.
Watch the full interview with Dr. Jha: