Sen. Angus King, I-Maine, left, Sen. Roger Wicker (R-MS)

Bill Clark/CQ-Roll Call, Inc via Getty Images; Tom Williams-Pool | Getty Images

Sens. Roger Wicker and Angus King, who are both vaccinated for the coronavirus, tested positive for Covid-19 on Thursday after experiencing symptoms.

Wicker, a Republican from Mississippi, and King, an independent from Maine, are the latest in a string of prominent politicians to announce positive coronavirus tests in recent weeks despite being fully vaccinated. Others include Republicans Sen. Lindsey Graham of South Carolina and Gov. Greg Abbott of Texas.

“Senator Wicker is fully vaccinated against COVID-19, is in good health, and is being treated by his Tupelo-based physician,” Phillip Waller, Wicker’s communications director, said in a statement. The 70-year-old Wicker “is isolating, and everyone with whom Senator Wicker has come in close contact recently has been notified.”

The Senate is in recess this week, and many of the chamber’s members are in home states either preparing for 2022 elections or checking in with district offices.

“Despite all my efforts, when I began feeling mildly feverish yesterday, I took a test this morning at my doctor’s suggestion, and it came back positive,” King, 77, said in a statement. “While I am not feeling great, I’m definitely feeling much better than I would have without the vaccine.”

Sen. Angus King (I-Maine) holds a chart as bipartisan members of the Senate and House gather to announce a framework for fresh coronavirus relief legislation at a news conference on Capitol Hill on Dec. 1, 2020.

Kevin Lemarque | Reuters

Wicker’s and King’s positive tests came as the Biden administration ramps up efforts to encourage Americans to seek booster shots starting next month amid a growing pool of data that shows vaccine protections fade over time.

Three of Washington’s top health experts on Wednesday provided further details on how the immune system’s protections wane over time.

It’s now “very clear” that immunity starts to fall after the initial two doses, and with the dominance of the delta variant, “we are starting to see evidence of reduced protection against mild and moderate disease,” according to a statement signed by CDC Director Dr. Rochelle Walensky, acting FDA Commissioner Dr. Janet Woodcock, White House chief medical advisor Dr. Anthony Fauci and other U.S. health leaders.

New Covid-19 cases are emerging at their highest rates since winter as the delta variant of the coronavirus sweeps across the U.S. Health experts blame its rapid spread for the uptick in case counts and deaths as a growing number of so-called “breakthrough” cases show fully vaccinated people are still at risk.

More than 140,000 new cases and 822 deaths were reported in the U.S. on Monday, according to the Centers for Disease Control and Prevention. The number of new daily deaths has more than doubled since the start of August.

The situation in Florida and Texas is especially grim, with case counts in both states blowing past records and overwhelming hospital systems.