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Miller tweeted Friday night and said she was "doing well."
"Thank you all for your prayers and well wishes. I’m doing well and look forward to getting back to work for the American people," she wrote.
Earlier, the White House had announced that an unnamed Pence staffer had contracted the virus. Two sources said Friday afternoon the aide is Miller.
"There is a member of the vice president's team who is positive for coronavirus," White House press secretary Kayleigh McEnany said at the briefing.
A senior administration official said the staffer tested positive for COVID-19 Friday morning.
"Wonderful young woman - Katie, she tested positive, she hasn't come in touch with me," President Trump said of Miller during a roundtable Friday. "It's the press person, tested positive out of the blue."
Miller is married to senior White House adviser Stephen Miller.
In light of the news, all members of the White House press corps at the White House were offered free COVID-19 tests as a precaution.
This is the second member of the vice president’s staff to test positive for COVID-19 in recent days. The news came one day after the White House revealed a person working as a valet for President Trump tested positive for the virus.
“We have put in place the guidelines our experts have put forward to keep this building safe,” McEnany said. “All of the recommended guidelines we have for businesses that have essential workers were now putting in place here in the White House, so as America reopens safely the white house is continuing to operate safely.”
The president and vice president, along with those in their close circle, are tested daily for coronavirus, an administration official said, and the aide who tested positive exhibited no symptoms. The person was tested yesterday and results came back negative, the official added.
Pence is traveling Friday to meet with faith leaders in Des Moines, Iowa to discuss reopening houses of worship. Later, he’ll meet with agricultural and food leaders in Iowa to discuss steps to keep the food chain secure.
Pence’s flight on Air Force 2 was delayed about an hour Friday morning because of the staffer's positive test, the senior administration official said. The person who tested positive was not on the plane and not scheduled to be on the trip, but those who had contact with the person were asked to go home and get tested "out of an abundance of caution," according to the official.
In March, another staff member in Pence’s office tested positive for coronavirus, making that the first White House staffer known to have the virus.
Fox News’ Kristin Fisher, Sally Persons and Kellianne Jones contributed to this report.