• About 66,000 new Covid-19 cases are being reported in the U.S. each day, based on a seven-day average of Johns Hopkins University data. That is far below January's peak of about 250,000 daily cases but more in line with the summer surge, when daily cases peaked near 70,000 in late July.
• Nearly 2.4 million vaccine shots were administered on Monday, bringing the seven-day average of daily vaccinations to 2.8 million, a record level.

Amid growing fears of a fourth wave of U.S. Covid-19 cases, government officials urged Americans to continue taking precautions to prevent the spread of the virus.

During a press conference on Monday, Centers for Disease Control and Prevention Director Dr. Rochelle Walensky said she had a feeling of "impending doom" and urged Americans to "just hold on a little longer." Later in the day, President Joe Biden said the "war against Covid-19 is far from won." He condemned behavior likely to spread infections and said some states should pause their reopening plans.

At the same time, a new CDC study of vaccinated health-care workers showed that one dose of the Pfizer or Moderna vaccine was 80% effective in preventing coronavirus infections, and 90% two weeks after the second dose. The pace of daily vaccinations is nearing 3 million shots per day.

U.S. Covid cases

About 66,000 new Covid cases are being reported in the U.S. each day, based on a seven-day average of Johns Hopkins University data that has been ticking upward. That figure is far below January's peak of about 250,000 daily cases but more in line with the summer surge, when daily cases peaked near 70,000 in late July.

Cases are increasing by 5% or more, based on the change in the seven-day average of daily cases from a week ago, in more than half of U.S. states.

U.S. Covid deaths

The U.S. is reporting a weekly average of 990 Covid deaths per day, according to Hopkins data. Overall, more than 550,000 total U.S. coronavirus deaths have been reported.

U.S. vaccine shots administered

Nearly 2.4 million vaccine shots were reported administered on Monday, bringing the seven-day average of daily vaccinations to 2.8 million, a record level.

Biden said Monday that 90% of adults in the U.S. will be eligible for Covid shots by April 19.

"For the vast, vast majority of adults, you won't have to wait until May 1. You'll be eligible for your shot on April 19," Biden said

U.S. share of the population vaccinated

CDC data shows that 95 million people, nearly 30% of the U.S. population, have received at least one dose of a Covid vaccine. Some 53 million are fully vaccinated with two shots of the Pfizer or Moderna vaccines or one shot of Johnson & Johnson's.

About half of those 65 and older are fully vaccinated, according to the CDC.

CNBC's Noah Higgins-Dunn and Berkeley Lovelace Jr. contributed to this report.