(CNN) Three Democratic members of Congress announced Sunday that they have breakthrough coronavirus infections.
Sens. Elizabeth Warren of Massachusetts and Cory Booker of New Jersey as well as Rep. Jason Crow of Colorado shared that they had tested positive for Covid-19 via tweets from their official accounts.
They all reported having received Covid-19 booster shots and experiencing mild symptoms.
Warren was on the Senate floor last week before the chamber went on recess, but CNN could not confirm that Booker was.
"I regularly test for COVID & while I tested negative earlier this week, today I tested positive with a breakthrough case. Thankfully, I am only experiencing mild symptoms & am grateful for the protection provided against serious illness that comes from being vaccinated & boosted," Warren tweeted. "As cases increase across the country, I urge everyone who has not already done so to get the vaccine and the booster as soon as possible - together, we can save lives."
Crow tweeted that he "just returned from an official congressional delegation visit to Ukraine and tested positive for a breakthrough COVID infection."
The announcements came as the emergence of the Omicron variant has thrust the nation -- and the White House -- back into an uncertain pandemic reality, posing both public health and political challenges.
The US is now facing a resurgent coronavirus as the pandemic marches into its third year: The country was averaging 126,967 new cases per day as of Saturday, according to data from Johns Hopkins University -- up from an average of just more than 70,000 new cases per day at the beginning of November.
The country is likely in for a hard winter as the new variant strains a health care system already battered by the Delta variant, Dr. Anthony Fauci said Sunday.
"It's going to take over," Fauci, the nation's top infectious disease expert, said of the Omicron variant on CNN's "State of the Union" Sunday, urging Americans to get vaccinated and get their booster shots. "And be prudent in everything else you do: When you travel in your indoor settings that are congregated, wear a mask."
According to the World Health Organization, Omicron cases are doubling every 1.5 to 3 days with documented spread. And in the US, it's expected to become the "dominant strain" in the coming weeks, the US Centers for Disease Control and Prevention Director Dr. Rochelle Walensky said Friday.
This story has been updated with additional information Sunday.