Three fully vaccinated Democratic members of Congress tested positive for COVID-19 on Sunday.  

The breakthrough cases were announced by Sens. Elizabeth Warren of Massachusetts and Cory Booker of New Jersey. Both Warren and Booker ran for president in 2020.  

Rep. Jason Crow of Colorado also tested positive for COVID. The three received a COVID-19 booster shot and are reportedly experiencing mild symptoms.  

“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.”  

The COVID-19 pandemic has plagued the world for two years in a row, and is having a resurgence heading into year three.  

Related: South African President Cyril Ramaphosa Contracts ‘Mild’ Case of COVID-19  

According to data from Johns Hopkins University, as of Saturday, the US is averaging 126,967 new cases a day, which is up from an average of 70,000 new cases per day at the start of November.  

First detected in Botswana and South Africa last month, the Omicron variant has spread quickly worldwide. 

The variant was first identified in the US on Dec. 1 and has been reported in 45 states as of Monday.  

According to the CDC, the Omicron variant will likely spread more quickly than the original COVID-19 virus. It is still unknown how Omicron spreads compared to the Delta variant.   

The CDC said anyone who has contracted the Omicron variant could spread the virus to others, even if they are fully vaccinated.  

COVID-19 vaccinations are still the No. 1 source of protection against the virus to prevent severe illness, hospitalizations and deaths. 

Related: Nigeria To Discard 1 Million Expired COVID-19 Vaccines