A fully vaccinated White House official tested positive for COVID-19 off site and has mild symptoms but was not found to have had close contacts with White House principals or staff, White House press secretary Jen Psaki said on Tuesday.

The official remains off White House grounds pending additional testing for confirmation, she said. The White House medical unit had conducted contact tracing and interviews, finding no close contact among staff and President Joe Biden.

Psaki also said there had been other instances of vaccinated employees testing positive, though they were not commissioned officers and therefore were not reported by the administration.

"We committed that we would release information proactively if it is commissioned officers," she said. Commissioned officers work for the president and not for another White House official.

Asked whether the administration fears that these breakthrough cases will spur more vaccine hesitancy among Americans, Psaki said she hasn't seen any data to indicate this trend.

"We know that there will be breakthrough cases, but as this instance shows, cases in vaccinated individuals are typically mild," she said. "This is another reminder of the efficacy of the COVID-19 vaccines against severe illness or hospitalizations," she added.

Over the weekend, six Texas Democrats, who fled the state to thwart Republican efforts to pass new voting restrictions and were visiting Washington, tested positive for Covid-19. Vice President Kamala Harris met the lawmakers last week but has since tested negative, Psaki said.

A senior spokesperson for House of Representatives Speaker Nancy Pelosi, who was fully vaccinated and came in contact with the Texas lawmakers, has tested positive. The spokesperson has had no contact with Pelosi since being exposed to the virus, according to the speaker's office. (Reporting by Nandita Bose; Writing by Doina Chiacu; Editing by Chizu Nomiyama and Sandra Maler)