Biden tests positive for COVID. Again.

President Biden has tested positive for COVID ... again.

"This happens with a small minority of folks," the president tweeted Saturday afternoon. "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."

Presidential physician Kevin O'Connor explained that Biden's positive antigen test was the result of a rare "rebound" infection that can occur in patients taking the antiviral drug with which Biden was treated.

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"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 in a letter.

Biden initially tested positive on the morning of July 21. He then reportedly tested negative on Tuesday evening and on the following three mornings before testing positive on Saturday morning. Biden is double vaccinated and has received two booster shots.