If the results come back negative, they can stop wearing masks indoors. If results are positive, the infected should isolate at home for 10 days.
Although people who are fully vaccinated may still get infected with the virus, these breakthrough infections tend to be mild or asymptomatic. The vaccines authorized in the United States provide strong protection against the worst outcomes, including severe disease, hospitalization and death, including from the Delta variant.
The new testing recommendation came on the same day that the agency recommended that fully vaccinated people return to wearing masks indoors under some circumstances. When levels of community transmission are high, everyone, regardless of vaccination status, should wear masks indoors when they are in public, the agency now says.
The agency also recommended that vaccinated people in close contact with unvaccinated people, including children under age 12, consider wearing masks in public indoor spaces whatever the transmission rates in the local community. In a shift, the agency also recommended universal masking in schools.
For months, the C.D.C. had resisted recommending masks for vaccinated people, even as the highly contagious Delta variant spread and the World Health Organization recommended continued mask wearing.