Senators Roger Wicker, Republican of Mississippi, Angus King, independent of Maine, and John Hickenlooper, Democrat of Colorado, said on Thursday that they had tested positive for the coronavirus, adding to the number of breakthrough cases among lawmakers.
“Senator Wicker is fully vaccinated against Covid-19, is in good health and is being treated by his Tupelo-based physician,” his spokesman, Phillip Waller, said in a statement released by his office, adding that the senator was experiencing only mild symptoms.
The announcement from Mr. Wicker came as his home state has shattered previous records for new cases this week, and is now reporting more new cases relative to its population than any other state in the country. Mississippi is averaging 118 new cases a day for every 100,000 people, according to data compiled by The New York Times.
Mr. King’s statement said he was symptomatic but taking recommended precautions.
“While I am not feeling great, I’m definitely feeling much better than I would have without the vaccine,” he said. “I am taking this diagnosis very seriously, quarantining myself at home and telling the few people I’ve been in contact with to get tested in order to limit any further spread.”
Mr. Hickenlooper said on Twitter that he was experiencing limited symptoms and expressed gratitude to scientists who had developed the vaccine. He also encouraged vaccinated people to get booster shots in accordance with a plan that the Centers for Disease Control and Prevention announced this week.
The Senate is in recess this week after adjourning early last Wednesday, leaving it unclear whether any of the men had been in recent contact with other lawmakers, as well as when or where they were first exposed. Their diagnoses brings to 11 the number of senators who have tested positive so far, according to news reports compiled by Ballotpedia, a political data website; more than 50 members of the House have tested positive.
Several other vaccinated politicians have recently announced breakthrough cases of their own, including Senator Lindsey Graham of South Carolina, who said he tested positive for the virus after attending a gathering hosted by Senator Joe Manchin III of West Virginia.
On Tuesday, Gov. Greg Abbott of Texas tested positive and began receiving an antibody treatment, highlighting both the growing concerns over breakthrough cases in the United States and the political tensions over public health measures that Mr. Abbott has consistently opposed in his home state.
While Mr. Wicker has encouraged his constituents to get vaccinated and has applauded the national vaccination effort in official statements, he has also resisted elements of the Biden administration’s coronavirus response. In June, he introduced a resolution calling on the C.D.C. to end a mask mandate for vaccinated people on public transportation.
As the Delta variant spreads aggressively, infections in vaccinated people have been seen more frequently, though they are still rare. The surge and the rising frequency of breakthrough infections have prompted agencies to extend public health measures. The Transportation Security Administration said on Tuesday that the mask mandate would remain in effect on public transportation through Jan. 18.
