Sen. Lindsey Graham announced he would self-quarantine for 10 days Monday after revealing a positive COVID-19 test.

“I was just informed by the House physician I have tested positive for COVID-19 even after being vaccinated,” the South Carolina Republican said in a statement. “I started having flu-like symptoms Saturday night and went to the doctor this morning. I feel like I have a sinus infection and at present time I have mild symptoms.”

Graham is the first senator to announce a “breakthrough” case of COVID-19 despite being vaccinated and the first to say he had been sickened by the virus this year. He is the third member of Congress since mid-July to announce a positive test.

Graham said he was glad he got vaccinated, saying that without it, “My symptoms would be far worse.”

Rep. Vern Buchanan, a vaccinated Florida Republican, announced he was sickened by the virus on July 19. Rep. Clay Higgins, a Louisiana Republican, posted to Facebook that he and his family had tested positive for the virus a second time and completed a 10-day quarantine July 25. It’s not clear if he received a vaccine.  

Graham was one of 16 Republicans who joined Democrats in a 66-28 vote on Friday to proceed to the legislative vehicle for the bipartisan infrastructure package. It’s not clear what his 10-day absence will mean for the future of that bill.

Graham was reportedly in attendance over the weekend at an event on West Virginia Democratic Sen. Joe Manchin’s houseboat with other senators. The Centers for Disease Control and Prevention says people who are fully vaccinated do not need to self-quarantine after being in contact with someone who is positive for COVID-19 unless they’re symptomatic. 

The agency does advise fully vaccinated people to get tested three to five days after exposure, even if they don’t have symptoms, and to wear a mask indoors and in public for 14 days following exposure or until their test result is negative.

“Senator Manchin is fully vaccinated and following the CDC guidelines for those exposed to a COVID positive individual,” said a Manchin spokeswoman when asked whether Graham was in attendance at the event. 

Senators from both parties, including Graham, had been seen in the past several weeks moving around the Capitol without masks after the CDC relaxed masking rules for vaccinated people. Lately, more senators have been seen wearing masks.

Mask mandates were ordered back for the House and at the White House last week, as cases among vaccinated people have gone up, in part because of the highly contagious delta variant of the coronavirus. The Senate strongly encouraged people to pull their masks back out but did not mandate them. 

Attending Physician Brian Monahan sent messages to both the House and Senate last week, urging them to adhere to the new CDC guidance that called on fully vaccinated people to wear masks indoors in areas with significant spread. 

Reimposed mask rules didn’t sit well with some members of the House. On Thursday, some Republican members of the House protested the mandate on their side of the Capitol by walking over to the Senate’s chamber maskless and sitting in while GOP Sen. Mike Lee discussed the House mask rules. 

The House is now in recess, and not scheduled to return until September. 

Some GOP members had begun wearing masks before Graham’s announcement, including Sen. Lisa Murkowski, who was sporting one Monday. 

The Alaska Republican said she chose to begin wearing a mask again because Washington Mayor Muriel Bowser reimposed a masking policy, calling on businesses once again to enforce the wearing of masks indoors. 

The Capitol complex is not required to follow District of Columbia rules, but city guidance says fully vaccinated people who experience any symptoms suggestive of COVID-19 should isolate, see their healthcare provider and get tested if indicated.

“The District has imposed a mask mandate, and I respect the masking mandates,” Murkowski said. “Even though I don’t like to wear a mask, I will do that out of respect to everybody else.”