(CNN) — President Joe Biden has tested positive for Covid-19 and is experiencing “mild symptoms,” White House press secretary Karine Jean-Pierre said Thursday.

“This morning, President Biden tested positive for COVID-19. He is fully vaccinated and twice boosted and experiencing very mild symptoms. He has begun taking Paxlovid. Consistent with CDC guidelines, he will isolate at the White House and will continue to carry out all of his duties fully during that time,” she said.

This is the first time Biden, 79, has tested positive for Covid-19. He last tested negative on Tuesday, per Jean-Pierre, who added that he will take Paxlovid.

Paxlovid is Pfizer’s antiviral drug and is available via emergency use authorization from the US Food and Drug Administration for treatment of mild to moderate Covid-19 in people 12 and older who are at high risk of severe illness. It requires a doctor’s prescription.

Biden received his first two doses of the Pfizer/BioNTech Covid-19 vaccine ahead of his inauguration in January 2021, his first booster shot in September and his second booster vaccination on March 30.

Due to his age, Biden is at an increased risk for a more severe case of Covid-19, although the US Centers for Disease Control and Prevention says older adults being fully vaccinated and boosted significantly reduces their risk of hospitalization and death.

A wave of cases among Cabinet members, White House staffers and members of Congress has swept Washington in recent months.

Vice President Kamala Harris contracted the virus earlier this year. Harris is also fully vaccinated and double boosted and did not experience symptoms, according to her spokesperson Kirsten Allen. The President was not a close contact. The vice president took the antiviral coronavirus treatment Paxlovid after consulting her physicians, according to Allen, and tested negative on May 2, leaving isolation.

Secretary of State Antony Blinken and White House domestic policy adviser Susan Rice were some of the highest-ranking Biden administration officials to test positive for Covid-19 after the White House Correspondents’ Dinner in Washington in April. The President also attended the dinner and delivered remarks. All of the roughly 2,600 guests were required to be fully vaccinated and show proof of a negative test on the day of the event.

Defense Secretary Lloyd Austin, second gentleman Doug Emhoff, House Speaker Nancy Pelosi, Commerce Secretary Gina Raimondo, Attorney General Merrick Garland, then-White House press secretary Jen Psaki and several others have tested positive in recent months.

White House officials had acknowledged it was possible the President would at some point contract Covid-19 but have emphasized the precautions being taken to prevent infection.

“The bottom line is he is vaccinated and boosted. He is very well protected. He’s got very good protocols around him to protect him from getting infected. But there is no 100% anything,” White House Covid-19 response coordinator Dr. Ashish Jha has said.

The President’s infection comes as the US sees a rise of Covid-19 cases and more than 1 million people have died of Covid-19 since the pandemic began.

The Biden administration is continuing the Covid-19 public health emergency as it seeks new funding from Congress for treatments and vaccines. The public health emergency declaration allows many Americans to obtain free Covid-19 testing, therapeutic treatment and vaccines. Medicare has also relaxed the rules governing telehealth so that many more seniors can access such services during the declaration. And states are not involuntarily disenrolling residents from Medicaid during the declaration, in exchange for receiving more generous federal matching funds.

More than two years into the pandemic, Biden has become the second sitting US president to test positive for Covid-19. Then-President Donald Trump announced on October 2, 2020, that he and then-first lady Melania Trump had tested positive for Covid-19, months before any vaccines were authorized by the US Food and Drug Administration.

Later that day, Trump was transferred to Walter Reed, where he spent the weekend and received various treatments. Trump returned to the White House on October 5, 2020.

Biden underwent his annual physical in November at Walter Reed National Military Medical Center. His physician, Dr. Kevin O’Connor, wrote in a memo that the President “remains fit for duty, and fully executes all of his responsibilities without any exemptions or accommodations.”