“The agency is currently actively looking to update its recommendations for KN95 and N95 in light of omicron,” the official said. “We know these masks provide better filtration.”

When the CDC issued its initial mask guidance in 2020, health officials did not urge the use of the more protective face coverings out of concern that health workers might be unable to get them. But health officials said there are no longer serious shortages of N95 masks.

The updated guidance is expected to say that the best mask is the one that is worn consistently and correctly. N95 masks, which were predominantly used in health-care and industrial settings before the pandemic, are supposed to be individually fitted and are sometimes hard to wear all day, physicians and other health-care personnel have said. The CDC guidance is expected to say that if people can “tolerate wearing a KN95 or N95 mask all day, you should.”