Biden tests positive for Covid-19 again in a case of ‘Paxlovid rebound’ – STAT

President Biden tested positive for the coronavirus again Saturday, the White House said, an example of Covid-19 rebound that can occur after people take the oral antiviral Paxlovid.

Biden is not experiencing any symptoms but is isolating again, according to his physician, Kevin OConnor. Biden, who is vaccinated and has received two boosters, is not starting any Covid treatments at this time.

Biden, 79, first tested positive on July 21, and after a mild case, tested negative this past Tuesday. He tested negative each day the rest of the week the White House said he had upped his testing frequency following his infection but tested positive again Saturday morning.

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This in fact represents rebound positivity, OConnor wrote in a memo Saturday.

Such rebound cases following treatment with Pfizers five-day oral antiviral have stumped physicians as theyve tried to understand how frequently its occurring and whats allowing the virus to come back a second time.

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While some rebound cases are asymptomatic like Bidens thus far other people see their symptoms return.

Rebound cases have raised such questions as whether Paxlovid should be prescribed for longer courses and for which patients it should be recommended.

Pfizers clinical trials showed rebound in 1% to 2% of patients, but in both patients who took Paxlovid and those who received placebo. But there have been enough anecdotes about Paxlovid rebound that many infectious disease physicians believe the rate could be higher. Anthony Fauci also had a rebound case after taking Paxlovid.

One theory for whats allowing rebound is that the drug wipes out most of the virus before the body has a chance to recognize whats happening and build up its full immune arsenal. If there are little pockets that manage to survive the treatment, they can start replicating again once the course of Paxlovid is finished. Other experts have wondered if it has something to do with the Omicron variant specifically. (The trials took place when the Delta variant was dominant.)

Research to determine the cause is ongoing.

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Biden tests positive for Covid-19 again in a case of 'Paxlovid rebound' - STAT