President Biden said on Thursday afternoon that he tested positive for COVID-19.
In a video posted to Twitter Thursday afternoon, Biden said his symptoms continue to be mild.
"I guess you heard, this morning I tested positive for COVID. But I've been double vaccinated, double boosted. Symptoms are mild, and I really appreciate your inquiries and concerns," Biden said in the 20-second video. "But I'm doing well, getting a lot of work done. Going to continue to get it done, and in the meantime, thanks for your concern, and keep the faith. It's gonna be OK." 
Biden was unmasked while standing outside on the Truman Balcony at the White House in the video.
The video confirmed the announcement from the White House in a statement earlier on Thursday morning.
White House Press Secretary Karine Jean-Pierre wrote that Biden will work in isolation at the White House until he tests negative. She reiterated much of the statement at the daily White House press briefing, saying the president has continued working from the White House residence and has been in touch with staff throughout the day.
He also spoke with the Pennsylvania officials he was supposed to meet with today in an event highlighting the recently passed bipartisan legislation on gun reform.
“He's feeling tired, but he's working very hard on behalf of the American people,” Jean-Pierre said.
She also said the White House is, as of now, unaware of where exactly Biden may have been exposed to COVID-19.
According to the CDC, COVID symptoms may appear between two and 14 days after initial exposure to the virus. 
The president last week traveled to the Middle East and attended meetings with officials in Israel and the Palestinian territories before attending a summit of the Gulf Cooperation Council in Jeddah, Saudi Arabia. 
White House Coronavirus Response Coordinator Dr. Ashish Jha joined Jean-Pierre at Thursday’s briefing and underscored the importance of vaccination and early detection of COVID infections. He also said the president’s test has been sent off for sequencing to determine which variant he is infected with.
"Because the president is fully vaccinated, double boosted, his risk of serious illness is dramatically lower,” Dr. Jha said. “And it's a reminder of the reason that we all work so hard to make sure that every American has the same level of protection that the president has."
Jean-Pierre read a letter from Dr. Kevin O'Connor, the physician to the president, outlining the positive test result from an antigen test. She told reporters that Dr. O’Connor would not be made available today, despite the fact that he is the one directly administering treatment to the president.
O'Connor said in the letter that the president's "mild symptoms" include a runny nose and an occasional dry cough, which started Wednesday evening.
Jean-Pierre said the White House will provide a daily update of the president's status.
She also said Biden is taking Paxlovid, the early COVID treatment available to those who test positive and are at a high risk for developing severe COVID-19. Biden is 79 years old, putting him in one of the most high-risk age brackets.
"The President is fully vaccinated and twice-boosted," O'Connor wrote, "so I anticipate that he will respond favorably, as most maximally protected patients do. Early use of PAXLOVID in this case provides additional protection against severe disease."
Jean-Pierre also said the White House Medical Unit "will inform all close contacts of the President during the day today, including any Members of Congress and any members of the press who interacted with the President during yesterday's travel."
Biden on Wednesday traveled to Massachusetts and delivered remarks on climate change and announced new executive actions. His speech took place outdoors in front of a small crowd and with little interaction, as some members of the press corps have noted.
The president traveled with Massachusetts Sens. Elizabeth Warren (D) and Ed Markey (D) and Reps. Jake Auchincloss (D-4th District) and Bill Keating (D-9th District).
Keating, who is vaccinated and boosted, tweeted on Thursday that he tested negative after hearing the news of Biden's positive test.
First Lady Jill Biden is considered a close contact as well. She tested negative this morning while in Detroit for an event with Education Secretary Miguel Cardona.
Vice President Kamala Harris also tested negative, according to a White House official. She was last with Biden on Tuesday. Her Thursday schedule will remain unchanged, and she will remain masked on the advice of the White House Medical Unit.
Updated on July 21, 2022, at 4:09 p.m. ET with President Biden's video on Twitter.