The C.D.C. director offers a stark reassurance: Only unvaccinated people are at risk by unmasking.

The guidance the C.D.C. issued on Thursday said that it was no longer necessary for fully vaccinated people to mask or maintain social distance in many settings. The change set off days of public confusion and drew objections from some local officials and labor unions, including the country’s largest union of registered nurses. A number of major U.S. retailers have already lifted mask requirements, essentially turning to an honor system that relies on unvaccinated people to keep their masks on in public.

She also noted that communities where cases are high should consider keeping mask requirements, and that children who are not vaccinated — including everyone under 12 because they are not yet eligible for the shot — and people with compromised immune systems should keep their faces covered.

“This was not permission to shed masks for everybody everywhere,” Dr. Walensky said on NBC’s “Meet the Press,” but about “individual assessment of your risk.”