The number of people who have died from COVID-19 in the United States surpassed 800,000 on Tuesday, according to real-time data compiled by Johns Hopkins University's Center for Systems Science and Engineering.

The figure is greater than the approximately 700,000 Americans who have died from AIDS-related illnesses over the last four decades, and it's higher than the total number of U.S. troops who have fallen in battle since 1900.

Since last December, when the first COVID-19 vaccines were being administered, an additional 500,000 people in the U.S. have died from the virus.

Of those, some 230,000 have died since April 2021, when U.S. President Joe Biden announced COVID-19 vaccines were widely available to every American over the age of 18.

-ABC News' Arielle Mitropoulos

The U.S. saw a sevenfold increase in the prevalence of the omicron COVID-19 variant over the last week, according to data from the U.S. Centers for Disease Control and Prevention.

Just over two weeks after it was first discovered in the country, the omicron variant is now estimated to account for nearly 3% of all new cases in the U.S., the latest data from the CDC shows.

Last week, omicron accounted for an estimated 0.4% of all new cases, according to the data.

-ABC News' Arielle Mitropoulos

Dr. Anthony Fauci told CNN Tuesday that omicron will "for sure" become the dominant strain in the U.S. given how rapidly it is spreading.

"Omicron is going to be a challenge because it spreads very rapidly," Fauci said.

Fauci reiterated that omicron so far appears to be less severe, adding, "Whether it is inherently less pathogenic as a virus or whether there is more protection in the community, we're just going to have to see when it comes in the United States."

-ABC News' Arielle Mitropoulos

Cornell University is moving into a "level red" alert after a "significant" number of suspected omicron cases were detected among student samples.

"While we must await confirmatory sequencing information to be sure that the source is Omicron, we are proceeding as if it is," university president Martha Pollack wrote in a letter to the community.

All final exams will be online beginning Tuesday, Pollack announced, and libraries and fitness centers are closed.

All undergraduate events are canceled, as is Saturday's recognition ceremony for December graduates, Pollack said.

Cornell has recorded more than 600 confirmed cases among students and staff in the last week alone, according to the university dashboard. While no infected students are seriously sick, Pollack said the university has "a role to play in reducing the spread."

-ABC News' Arielle Mitropoulos, Chris Donato

The U.K. reported a 48.59 percent single-day increase in confirmed omicron cases Sunday.

And across the U.K. in the last seven days, there's been a 51.9 percent increase in new COVID cases. Hospitalizations are up 8.1 percent during that period. However, there's been a 6.5 percent decrease in new deaths compared to the preceding seven days.

On Sunday, the British government reported 82,886 new COVID cases and 45 new deaths. The government also confirmed 12,133 new cases of the omicron variant.

London's mayor declared a major incident in the capital Sunday because of the serious threat of omicron. In an interview with the BBC on Sunday, he said that in the last 24 hours, "we're at almost 30,000 confirmed new cases, and in the last seven days almost 130,000 confirmed new cases."

He said he's worried about the impact the increases are already having on frontline emergency services in London, adding there are a record number of absences that will hamper their ability to respond to people who are unwell.

-ABC News' Christine Theodorou