WASHINGTON: Donald Trump's national security advisor tested positive for Covid-19 Monday, as the president prepared to visit a North Carolina facility where one of the leading vaccine candidates is being manufactured.

Trump has placed his hopes in the emergence of a successful vaccine by this fall to both contain the country's still raging coronavirus outbreak and revive his faltering election hopes.

National security advisor Robert O'Brien is the latest and most senior White House aide to contract the virus.

He "has been self-isolating and working from a secure location off site," the White House said in a statement, adding that there was "no risk of exposure to the president or the vice president." Others who have been previously infected include Vice President Mike Pence's spokeswoman Katie Miller, and Kimberly Guilfoyle, a top fundraiser for the Trump campaign.