Charles, Prince of Wales, tested positive for COVID-19 on Thursday morning, according to a spokesperson for Clarence House, his official London residence.

The 73-year-old heir apparent to the British throne "is now self-isolating" and "is deeply disappointed not to be able to attend today's events in Winchester and will look to reschedule his visit as soon as possible," the spokesperson said.

It's the second time that Charles has contracted COVID-19. He previously tested positive in March 2020, early on in the pandemic before vaccines were available, but he had mild symptoms.

Both the Prince of Wales and his wife, Camilla, the Duchess of Cornwall, are fully vaccinated against COVID-19, a Clarence House spokesperson has said.

The couple attended a British Asian Trust event at the British Museum in London on Wednesday night, along with hundreds of other guests, including several British politicians such as Chancellor Rishi Sunak, Home Secretary Priti Patel and Health Secretary Said Javid. Adar Poonawalla, CEO of the Serum Institute of India, the world's largest manufacturer of vaccines, was also in attendance.

-ABC News' Zoe Magee

Washington became the latest state Wednesday to announce it will be easing mask requirements.

Gov. Jay Inslee said the state's outdoor mask mandate will be lifted on Feb. 18, and he will provide a date next week on when the indoor mask mandate will end.

The state health department has required that everyone ages 5 and older wear a mask at indoor public settings, as well as at outdoor events with 500 or more attendees, regardless of vaccination status.

The announcement comes as COVID-19 cases have been declining rapidly in the state.

Dr. Anthony told the Financial Times that the U.S. is "heading out of" the "full-blown pandemic phase" and that he hopes masks and other measures can be dropped entirely in the coming months.

“As we get out of the full-blown pandemic phase of COVID-19, which we are certainly heading out of, these decisions will increasingly be made on a local level rather than centrally decided or mandated," Fauci said. "There will also be more people making their own decisions on how they want to deal with the virus.”

“There is no way we are going to eradicate this virus,” Fauci cautioned. “But I hope we are looking at a time when we have enough people vaccinated and enough people with protection from previous infection that the COVID restrictions will soon be a thing of the past.”

-ABC News' Cheyenne Haslett

Illinois plans to lift its indoor mask mandate at the end of month, Gov. JB Pritzker said, citing "hospitalization rates declining faster than any other point in the pandemic."

"If these trends continue -- and we expect them to -- then on Monday, Feb. 28, we will lift the indoor mask requirement," he said Wednesday.

Masks will continue in Illinois schools "subject to pending litigation which impacts a number of schools," the governor's office said. "As the CDC reaffirmed just today, masks remain a critical tool to keep schools safe and open."

The governors of New York and Rhode Island also announced an end to their indoor mask mandates on Wednesday.