USA: Days after contracting Covid-19 for the second time, US President Joe Biden tested negative for the disease on Saturday.
President Biden is "feeling great," according to a statement from Biden's physician, Kevin O'Connor. His SARS-CoV-2 antigen test came back negative this morning.

Until a second negative test, 79-year-old Biden, according to his doctor, will remain in isolation at the White House.

The president's efforts to capitalize on a recent Democratic policy victory have been thwarted by his "rebound" case, which his doctor has linked to the antiviral drug Paxlovid.

Although he attended virtually, he postponed a visit to Michigan on August 2 to support a law subsidizing US semiconductor manufacturing to compete with China.

Biden's doctor said that his most recent antigen test came negative on Saturday morning. The president will maintain his strict isolation rules until a second test is negative, as previously stated, out of caution.

After initially testing positive on July 21 and then twice negative on rapid antigen tests, Biden was released from isolation six days later. He experienced some minor symptoms, such as runny nose, sore throat, fatigue and fever.

On July 30, the president tested positive for the second time in a similar case to some Covid-19 patients who take PaxLovid from Pfizer to treat their condition.

After a positive test, rebound cases are advised to remain in isolation for five days. If their symptoms are improving and they do not develop a fever, they are advised to end isolation, but continue to wear a mask for an additional five days without any travel restrictions.

As with Paxlovid, which Biden has hailed as a sign of America's progress in tackling the pandemic, Biden's case brought to light the problem of rebound cases in a small percentage of users.

Rebound cases often have few or no symptoms, but many people should resume isolation according to the CDC's recommendations. O'Connor said Biden only had a mild cough.

Pfizer's Chief Scientific Officer Mikel Dolston said the company is collaborating with the Food and Drug Administration to plan a study of paxclovid "retreatment" for individuals who test positive after testing negative.

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