COVID-19 updates: Elizabeth Warren tests positive

The senator says she's experiencing "mild symptoms."

ByMorgan Winsor, Emily Shapiro, Ivan Pereira, and Meredith Deliso
Last Updated: December 20, 2021, 12:51 AM EST

As the COVID-19 pandemic has swept the globe, more than 5.3 million people have died from the disease worldwide, including over 806,000 Americans, according to real-time data compiled by Johns Hopkins University's Center for Systems Science and Engineering.

About 61.4% of the population in the United States is fully vaccinated against COVID-19, according to data from the Centers for Disease Control and Prevention.

Latest headlines:

Here's how the news is developing. All times Eastern.
Dec 17, 2021, 9:00 AM EST

Harvard joins list of universities mandating boosters

Harvard University will require boosters for all eligible members of the community, school officials said Thursday.

Students walk outside the Smith Campus Center at Harvard University in Cambridge, Mass., July 8, 2020.
NurPhoto via Getty Images, FILE

Earlier this week, Harvard warned of an increase in cases, saying the rise can be attributed to social events following the Thanksgiving break.

Omicron is likely already on campus, university officials added.

Harvard joins a growing list of colleges and universities moving to require third doses next semester for those eligible. Other schools include Stanford, NYU, University of Notre Dame, Syracuse, Smith College and Wellesley College.

-ABC News' Arielle Mitropoulos

Dec 17, 2021, 8:13 AM EST

Illinois reports highest case number of the year

In Illinois, 11,858 new cases were reported on Thursday -- the highest daily case number of all of 2021, ABC Chicago station WLS reported, citing state health officials.

A woman walks out of a free COVID-19 testing site in Chicago, Dec. 10, 2021.
Nam Y. Huh/AP

Illinois confirmed its second omicron case Wednesday, detected in a suburban Chicago resident. That person is asymptomatic and vaccinated, WLS reported.

Dec 16, 2021, 8:52 PM EST

CDC recommends opting for Pfizer or Moderna over J&J when there's a choice

The Centers for Disease Control and Prevention has signed off on its advisory committee's recommendation that people who have a choice should get an mRNA vaccine, either Pfizer or Moderna, over the single-shot Johnson & Johnson vaccine.

The updated recommendation comes after a review of new CDC data on rare blood clots linked to the J&J vaccine.

"Today's updated recommendation emphasizes CDC's commitment to provide real-time scientific information to the American public," CDC Director Dr. Rochelle Walensky said in a statement. "I continue to encourage all Americans to get vaccinated and boosted."

Dec 16, 2021, 7:54 PM EST

Omicron now makes up nearly 100% of strains found in Orlando wastewater samples

The new omicron variant makes up nearly 100% of the strains found in wastewater samples in Orlando, Florida, officials said Thursday.

"It escalated rapidly," Orange County Utilities spokeswoman Sarah Lux told ABC News.

In its first test for the variant last Thursday, the department found no evidence of omicron in the community's wastewater, she said. On Saturday, it represented about 30% of the strains found in the samples, and by Tuesday, nearly 100%.

"So, we're talking about zero to nearly 100 in a matter of a week," Lux said.

All parts of the county are seeing an increasing presence of the omicron variant, she said. The southern area, home to the theme parks, has seen the highest amount of virus remnants, followed by the eastern area, which is home to the University of Central Florida.

-ABC News' Arielle Mitropoulos