U.S. Sen. Lindsey Graham of South Carolina announced Monday he has contracted the coronavirus.

“I was just informed by the House physician I have tested positive for #COVID19 even after being vaccinated,” Graham said on Twitter. “I started having flu-like symptoms Saturday night and went to the doctor this morning.”

Graham described his symptoms as like “a sinus infection and at present time I have mild symptoms.”

Graham, a Republican who won reelection in November, said he will quarantine for 10 days.

“I am very glad I was vaccinated because without vaccination I am certain I would not feel as well as I do now,” he wrote. “My symptoms would be far worse.”

On Monday, Johns Hopkins University of Medicine said it has recorded more than 35 million cases of the coronavirus in the U.S. since the pandemic began.