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 CDC's advisory committee recommended Thursday that people who have a choice should get an mRNA vaccine, either Pfizer or Moderna, over the single-shot Johnson & Johnson vaccine after a review of new CDC data on rare blood clots linked to J&J.

The vote was unanimous.

The rare blood clots are not a new safety concern and the vaccine has already become far less common in the U.S. after it was given an FDA warning label about the clotting condition. But more data that confirmed a slightly higher rate of clotting cases and deaths than was previously reported caused the CDC and FDA to take another look at the data this week.

The CDC has confirmed nine deaths and 54 cases from the severe clotting event, thrombosis with thrombocytopenia.

There could also be more cases and deaths because TSS is under-diagnosed and could be underreported, the CDC said.

The clotting is more common among women in their 30s and 40s but has been seen in adult men and women of all ages.

The experts said J&J should not be taken off the shelves and is still far more beneficial than not getting any vaccine at all.

-ABC News' Cheyenne Haslett