Democratic vice-presidential candidate Kamala Harris will halt campaign travel until Monday after two members of her staff tested positive for coronavirus.
The California senator’s communications director, Liz Allen, and a flight crew member received the results on Wednesday, a Biden official said.
Neither aide had close contact with the candidates in the 48 hours prior to their positive tests, she added.
Ms Harris had been scheduled to fly to North Carolina on Thursday.
Biden Campaign Manager Jen O’Malley Dillon said the senator had no close contact with either infected staff member in the two days before the positive test, and was therefore not required to quarantine.
“Regardless, out of an abundance of caution and in line with our campaign’s commitment to the highest levels of precaution, we are cancelling Senator Harris’s travel through Sunday,” she said.
An airline company staff member who flew with presidential candidate Joe Biden on Monday and Tuesday also tested positive, Ms Dillon said in a statement.
Mr Biden was not in close contact with the individual, his team said, and doctors advised that he did not need to self-isolate.
On 8 October, Ms Harris and Mr Biden campaigned together in Arizona, where they held multiple appearances and interviews. The campaign says Ms Harris flew with both staff members on that trip, but they all wore masks throughout the flight and practiced social distancing.
Ms Harris and her husband both tested negative on Thursday, the campaign told reporters.
The Biden campaign has made emphasising health safety a visible part of its political strategy, in an effort to mark a point of contrast with President Trump. A number of Republicans and White House associates – and Mr Trump himself – have tested positive for coronavirus in recent weeks.
Mr Biden is scheduled to hold a town hall event on ABC News on Thursday night. President Trump is due to host a competing town hall on NBC at the same time.