President Biden posted a video to social media on Saturday afternoon after testing positive for COVID-19 in a "rebound" case.

"Hey folks, Joe Biden here. Tested positive this morning. Going to be working from home for the next couple of days. And I'm feeling fine, everything's good. But Commander and I got a little work to do," Biden said in the video posted to Twitter.

White House Doctor Dr. Kevin O'Connor said in a letter on Saturday afternoon that a small number of people who take Paxlovid to treat COVID-19 test positive for the virus after testing negative.

"As described last week, acknowledging the potential for so-called ‘rebound’ COVID positivity observed in a small percentage of patients treated with PAXLOVID the President increased his testing cadence, both to protect people around him and to assure early detection of any return of viral replication," O'Connor said.

BIDEN TESTS POSITIVE FOR COVID IN 'REBOUND' CASE, DOCTOR SAYS

President Biden video

President Biden posted a video to Twitter on Saturday afternoon after testing positive for COVID-19 in a "rebound" case. (President Biden/Twitter)

Biden tested positive for COVID-19 on Saturday morning after using an antigen test.

The infection represents "rebound positivity," adding that Biden has not displayed coronavirus symptoms.

Biden will begin "strict isolation procedures," O'Connor said.

"Folks, today I tested positive for COVID again. This happens with a small minority of folks. I’ve got no symptoms but I am going to isolate for the safety of everyone around me. I’m still at work, and will be back on the road soon," Biden tweeted after testing positive on Saturday.

BIDEN 'PLAYED TOO LOOSE' WITH CDC'S MASK GUIDANCE AFTER NEGATIVE COVID TEST, DOCTOR SAYS: 'NOT A GOOD LOOK

President Biden in meeting with CEO's

US President Joe Biden speaks in the Eisenhower Executive Office Building in Washington, D.C., US, on Thursday, July 28, 2022. The drumbeat of recession grew louder after the US economy shrank for a second straight quarter, as decades-high inflation undercut consumer spending and Federal Reserve interest-rate hikes stymied businesses and housing.  (Photographer: Oliver Contreras/Bloomberg via Getty Images)

Biden initially tested negative for COVID-19 on Wednesday.

Dr. Marc Siegel, Fox News medical analyst and professor of medicine at New York University Langone Medical Center told Fox News Digital that he thinks some people who take Paxlovid experience a reemergence of the virus because of leftover COVID-19 particles.

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President Biden sitting

US President Joe Biden meets with chief executive officers on economic conditions in the Eisenhower Executive Office Building in Washington, D.C., US, on Thursday, July 28, 2022. The drumbeat of recession grew louder after the US economy shrank for a second straight quarter, as decades-high inflation undercut consumer spending and Federal Reserve interest-rate hikes stymied businesses and housing.  (Photographer: Oliver Contreras/Bloomberg via Getty Images)

"What I think happens is that the Paxlovid stops the virus from reproducing but when it wears off there may still be some particles left and they then start to reproduce again and the test turns positive. I think the FDA should consider extending the course to 7-8 days in higher-risk cases like the president," Siegel said.