WASHINGTON (AP) — Three senators said Thursday they have tested positive for COVID-19 despite being vaccinated, a high-profile collection of breakthrough cases that comes as the highly infectious delta variant spreads rapidly across the United States.

Sens. Angus King, I-Maine, Roger Wicker, R-Miss., and John Hickenlooper, D-Colo., all said they have tested positive for the virus. Almost every member of the Senate spent long hours together on the chamber's floor last week in an all-night session of budget votes before leaving town for August recess.

King said he began feeling feverish Wednesday and took a COVID test at his doctor’s suggestion. “While I am not feeling great, I’m definitely feeling much better than I would have without the vaccine,” King said.

Wicker’s office said he tested positive for the virus Thursday morning.

“Senator Wicker is fully vaccinated against COVID-19, is in good health, and is being treated by his Tupelo-based physician,” a statement from his staff read. “He is isolating, and everyone with whom Senator Wicker has come in close contact recently has been notified.”

Hickenlooper announced his positive test a few hours later.

“I feel good but will isolate per docs instructions. I’m grateful for the vaccine (& the scientists behind it!) for limiting my symptoms,” Hickenlooper tweeted. “If you haven’t gotten your shot—get it today! And a booster when it’s available too!”

The breakthrough cases emerged the day after U.S. health officials announced plans to dispense COVID-19 booster shots to Americans. They said the shots are needed to shore up their protection against the delta variant amid signs that the vaccines’ effectiveness is waning over time.

Sen. Lindsey Graham, R-S.C. had announced Aug. 2 that he had tested positive for COVID-19 despite being vaccinated. “Sending best wishes for a speedy recovery to my good friends and colleagues," he tweeted Thursday.

“If you have not already done so please #GetVaccinated," Graham added.

Dozens of members of Congress have reported testing positive for COVID-19. Rep. Ron Wright, R-Texas, 67, died from the disease early this year while Rep.-elect Luke Letlow, R-La., 41, died in December before being sworn into office.