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.”

In a statement issued Monday afternoon, the South Carolina Republican 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 attended an event over the weekend hosted by Sen. Joe Manchin on his houseboat and attended by other senators. 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.”

There’s no way to know just how risky it was for the people who were near Graham — vaccinated or not. Vaccinated people are at a much lower risk of being infected at all and for contracting a serious case. But the level of risk depends on whether he was masked, whether they were masked, how much virus his body was producing when they met, how close they were and for how long.

Manchin received his second dose of the vaccine earlier this year. According to the Centers for Disease Control and Prevention, fully vaccinated people determined to have been in close contact with someone who has COVID-19 do not need to quarantine if they are asymptomatic but should be tested within 5 days and wear a mask indoors for 4 days or until testing negative.

Graham, who was vaccinated in December, has long been a proponent of vaccination, saying during a visit this spring to the Medical University of South Carolina in Charleston that “the sooner we get everybody vaccinated, the quicker we can get back to normal.”

Graham's infection comes on the heels of updated CDC guidance urging even fully vaccinated people to return to wearing masks indoors in areas of high coronavirus transmission, citing the surge of the highly contagious delta variant. Recent analysis has shown that breakthrough cases of COVID-19, with mild or no symptoms, still remain rare.

Both congressional chambers have been adopting stricter face covering regulations amid a resurgence in COVID-19 cases across the country. The House has returned to a mask requirement, while the Senate has recommended medical-grade face coverings.

Graham, who was wearing a mask, did not answer questions from reporters on Capitol Hill earlier Monday, prior to the statement being issued. Because of Senate votes, Graham was not in attendance at Friday night’s Silver Elephant dinner, the South Carolina Republican Party’s signature annual fundraiser and an event attended by hundreds, including former Secretary of State Mike Pompeo, a headlining speaker.