The CDC is also urging vaccinated people in certain areas of the country to resume wearing masks because of Covid-19.

People in areas with high or substantial Covid-19 transmission should resume wearing masks, the CDC is expected to say, according to sources familiar with the announcement.

Current CDC guidance states that all people age 2 and older who are not fully vaccinated should wear masks at school.

CNN earlier reported that top officials met on Sunday night to go over the new data and evidence regarding the transmissibility of the variant and breakthrough cases, according to a person familiar with the meeting.

Two months ago, when the CDC updated mask guidance saying most who are fully vaccinated could go without masks indoors, the guidance moved so quickly that administration officials were informed less than a day before.

That's exactly what they will do and what they will provide specific details on later this afternoon."

A senior administration official said the decision was spurred by the more transmissible Delta variant.

"It's based on the fact that the Delta variant is clearly more transmissible than the prior ones," the official said.

New evidence found that the levels of virus found in breakthrough cases among the vaccinated people are similar to those found in unvaccinated individuals who contract coronavirus, raising concerns that vaccinated individuals may be able to spread the virus, the official said.