Elizabeth Warren has tested positive for COVID-19. The Mass. Senator announced her diagnosis on Sunday.

“I regularly test for COVID and while I tested negative earlier this week, today I tested positive with a breakthrough case,” Warren stated through her official Twitter. “Thankfully, I am only experiencing mild symptoms and am grateful for the protection provided against serious illness that comes from being vaccinated and boosted.”

Warren continued her statement by imploring the public to receive booster vaccinations against COVID-19 to assist in mitigating the spread of the virus and softening its potential symptoms: “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.”

News of Sen. Warren’s diagnosis comes amid renewed concern regarding COVID-19 and its new, more transmissible Omicron variant. The variant was first reported by researches in South Africa in November. The first U.S. case was discovered in early December. Now, the World Health Organization believes that U.S. cases of Omicron are doubling every one-and-a-half to three days, with experts projecting it will become the dominant strain of COVID-19 during the next few weeks. Yesterday, the state of New York broke its highest single-day COVID-19 diagnosis count for the second consecutive day.

President Joe Biden is expected to address the nation on Tuesday with a speech focusing on the threat of the Omicron variant.

“We are going to see a significant stress in some regions of the country on the hospital system, particularly in those areas where you have a low level of vaccination,” chief medical advisor Dr. Anthony Fauci warned in an appearance on Sunday’s edition of CNN’s “State of the Union.” “[That’s] one of the reasons why we continue to stress the importance of getting those unvaccinated people vaccinated.”