US senators Elizabeth Warren and Cory Booker have confirmed they have tested positive for Covid-19, as the US deals with another surge in cases and the emergence of the Omicron variant.

Warren, a progressive Democrat who ran for the presidential nomination in 2020, tweeted that she was vaccinated, had received her booster shot and was experiencing mild symptoms in a breakthrough case of the virus.

“Thankfully, I am only experiencing mild symptoms and am grateful for the protection provided against serious illness that comes from being vaccinated and boosted,” the Massachusetts senator wrote, using the occasion to also urge anyone not vaccinated to do so.

Warren, 72, didn’t elaborate on where she might have contracted the virus but said she was regularly tested and had returned a negative result earlier this week.

Her office did not respond to an email seeking comment.

Booker, a Democratic senator for New Jersey who also ran for president in 2020, said in a statement on Sunday he had tested positive for Covid after feeling symptoms a day earlier.

“Fortunately, my symptoms are relatively mild. I’m beyond grateful to have received two doses of vaccine and, more recently, a booster – I’m certain that without them I would be doing much worse. I encourage everyone who is eligible to get vaccinated and boosted,” he said.

Warren was at the US Capitol this week along with other senators as Democrats sought to pass Joe Biden’s $1.75tn Build Back Better social and environment bill.

That effort resulted first in delay and then, on Sunday, in fury, as the West Virginia senator Joe Manchin, a centrist and therefore key vote in the 50-50 chamber, said he would not support the bill.