The Centers for Disease Control and Prevention was expected to backpedal Tuesday on its masking guidelines and recommend that even vaccinated people wear masks indoors in parts of the U.S. where the coronavirus is surging, a federal official said.

The official spoke on condition of anonymity because the person was not authorized to discuss details of the new policy.

The CDC was expected to make an announcement later in the day.

For much of the pandemic, the agency advised Americans to wear masks outdoors if they were within 6 feet of one another.

Then in April, as vaccination rates rose sharply, the CDC eased its guidelines on the wearing of masks outdoors, saying that fully vaccinated Americans no longer needed to cover their faces unless they were in a big crowd of strangers. In May, the guidance was eased further for fully vaccinated people, allowing them to stop wearing masks outdoors in crowds and in most indoor settings.

The guidance still called for wearing masks in crowded indoor settings, like buses, planes, hospitals, prisons and homeless shelters, but it cleared the way for reopening workplaces and other venues.

Subsequent CDC guidance said fully vaccinated people no longer needed to wear masks at summer camps or at schools, either.

For months COVID cases, deaths and hospitalizations were falling steadily, but those trends began to change at the beginning of the summer as a mutated and more transmissible version of the coronavirus, the delta variant, began to spread widely, especially in areas with lower vaccination rates.

In recent weeks, a growing number of cities and towns have restored indoor masking rules. St. Louis, Savannah, Georgia, and Provincetown, Massachusetts, are among the places that reimposed mask mandates this month.