Relapse after Paxlovid: Why Biden is corona positive again

US President Biden has Corona for the second time - and that within just one week.

Relapse after Paxlovid: Why Biden is corona positive again

US President Biden has Corona for the second time - and that within just one week. As soon as the 79-year-old is out of isolation, he has to go back. The Covid drug Paxlovid is said to be responsible. In rare cases, a relapse can occur.

Just a few days ago, Joe Biden left isolation after his corona infection. However, the US President has now tested positive for the virus again. How can that be? This probably has little to do with bad tests or an extremely rapid reinfection. A corona drug with which the 79-year-old was treated is said to be responsible.

Last Thursday, Biden's corona test was positive for the first time. His doctors then prescribed him the Covid drug Paxlovid. The preparation, which is also approved in Germany, prevents corona viruses from multiplying in the body. Paxlovid must be taken for five days, starting within five days of the onset of symptoms or the suspected time of infection.

In fact, the drug worked for Biden — at least for now. After five days, the US President was negative. But then a problem that was rare with Paxlovid treatment arose: the so-called rebound effect. A study by the manufacturer Pfizer showed that the virus can flare up again in around two percent of the patients treated. Same with Biden: "Guys, I tested positive for Covid again today. That happens to a small minority. I have no symptoms, but I will isolate myself for the safety of everyone around me," he wrote on Twitter.

It has been known for months that Covid disease can return shortly after treatment with the drug Paxlovid. The US health authority CDC sees the very rare phenomenon calmly. Such a "Covid rebound" usually occurs two to eight days after an initial recovery, she wrote in May. A special therapy is then not necessary, but you should go into isolation for five days.

Stefan Kluge, Director of the Clinic for Intensive Care Medicine at the University Hospital Hamburg-Eppendorf, sees it that way. A rebound occurs in less than five percent of patients treated with Paxlovid, he told the dpa. Medically, according to the current state of knowledge, this is not a major problem.

One reason for the sudden return of corona could be that the virus cannot be reached by Paxlovid in some tissues and is therefore not completely killed. "The drug does not work like an antibiotic," explains Bernd Salzberger from the University Hospital in Regensburg. "By stopping the virus from multiplying, it gives the body time to build up its own immune protection and end the infection more quickly."

The duration of the treatment is not very long at five days, and remaining viruses could possibly multiply again afterwards, says Salzberger, who is also chairman of the German Society for Infectious Diseases. In addition, it cannot be ruled out that taking the drug could lead to the development of resistance.

So far, however, there is only limited reliable scientific knowledge about what triggers a relapse after Paxlovid treatment or makes it more likely. A first study by the University of San Diego in mid-June found no evidence that a relapse was associated with resistance or an immune deficiency in the patient. "Covid-19 rebound appears to be the result of insufficient exposure to the drug," the university said in a statement.

It is rather unlikely that Biden infected other people after his release from isolation. How infectious a person is depends primarily on the viral load in the body. The Paxlovid active ingredient nirmatrelvir disrupts the function of an enzyme that is central to virus replication. If the viral load falls, as has apparently been the case with Biden in the meantime, the patient is no longer contagious. Nevertheless, regular testing after the end of treatment makes sense to rule out a rare relapse. Biden was also tested daily after his isolation.

Paxlovid has been approved in the US since December 2021 and in Europe since January 2022. It was hailed as a miracle cure and gave great hope in the fight against the pandemic. In Germany, the preparation has so far been prescribed with caution, says the Hamburg expert Kluge. One reason for this is probably the fact that Paxlovid interacts with many other drugs. The intake should be checked carefully by a doctor.

In general, Paxlovid is recommended for patients who are not seriously ill but are at high risk of being hospitalized - for example because of their age. According to one study, it reduces the risk of hospitalization by almost 90 percent compared to a placebo. If a patient has a relapse, manufacturer Pfizer recommends repeat treatment with Paxlovid. According to the US health authority FDA, however, there is no evidence to date that longer or repeated treatment makes sense. Biden is also not receiving the drug again at this time.

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