US President Joe Biden has tested positive for Covid-19 again, in what has been described as a “rebound” infection by his doctor.

The 79-year-old first contracted the virus on 21 July, when he was revealed to be experiencing mild symptoms.

On Saturday Mr Biden said he was not experiencing symptoms but would isolate “for the safety of everyone around me”.

The president had tested negative for the virus four times between Tuesday and Friday last week.

In a letter describing the situation, Mr Biden’s physician Dr Kevin O’Connor said there was no need to resume treatment but the president would remain under “close observation”.

Mr Biden has been taking Paxlovid, an antiviral medicine which Dr O’Connor said had led to a “small percentage” of Covid patients experiencing a “rebound” test.