COLUMBIA, S.C. (AP) — Sen. Lindsey Graham has become the first senator to disclose a breakthrough infection after being vaccinated against the coronavirus, saying Monday he is "very glad" he received the vaccine, without which his current symptoms would be "far worse."

The news prompted several other lawmakers to get quick COVID-19 tests and report their status. A handful of Senate colleagues spent part of the weekend working and socializing with the South Carolina Republican, who attended a gathering on Sen. Joe Manchin's houseboat the evening that he first developed symptoms.

In a statement issued Monday afternoon, Graham said he "started having flu-like symptoms Saturday night" and went to the doctor Monday morning.

After being notified of his positive test, Graham said he would quarantine for 10 days.

"I feel like I have a sinus infection, and at present time, I have mild symptoms," the 66-year-old Graham said. "I am very glad I was vaccinated because without vaccination, I am certain I would not feel as well as I do now. My symptoms would be far worse."

According to spokesman Kevin Bishop, Graham was among senators who attended Manchin's event on Saturday. Sam Runyon, a spokeswoman for Manchin, said the West Virginia Democrat "is fully vaccinated and following the CDC guidelines for those exposed to a COVID positive individual."

In the Capitol Monday evening, senators who attended the gathering were present and voting. Manchin said he had since tested negative and said the outdoor event, which lasted several hours and featured hamburgers, was "just trying to get people together."

"We do everything in a bipartisan way, and that's what we do," Manchin said. "I talked to Lindsey today, he's fine."

Sen. Chris Coons, D-Del., told reporters that he was also on the boat, named "Almost Heaven," and was awaiting test results. Sens. John Thune, R-S.D., and Jacky Rosen, D-Nev., were also there and were getting tested.

More senators have donned masks in recent weeks as coronavirus case counts have risen, but they aren't required in the chamber, and some still choose not to wear them. The House has returned to a mask requirement.