A fully vaccinated White House official tested positive for COVID-19 but was found to have had no close contact with White House principals or staff, White House Press Secretary Jen Psaki said Tuesday.

"Yesterday, a fully vaccinated White House official tested positive for COVID-19 off campus. In accordance with our rigorous COVID-19 protocols, the official remains off campus as they wait for confirmatory PCR (polymerase chain reaction) test," said Psaki during Tuesday's press briefing, confirming earlier local media reports of the breakthrough case.

A PCR test is used to detect genetic material from a specific organism, such as a virus. 

She said the White House medical unit has done contact tracing and interviews, finding no close contact among White House principals, staff or President Joe Biden.

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

A senior spokesperson for House of Representatives Speaker Nancy Pelosi has also tested positive after coming into contact with Democrats from the Texas state legislature last week.

The spokesperson was fully vaccinated and had no contact with Pelosi since being exposed to the virus, according to the speaker's office.

COVID-19 cases are on the rise again in the United States as the highly transmissible Delta variant takes hold and vaccination efforts stagnate in the country.

Biden urged all Americans to remain vigilant in the fight against COVID-19, especially with the rise of the Delta variant, during his second full Cabinet meeting of his administration on Tuesday.

"The safest thing to do is to get vaccinated, get vaccinated," said Biden.

The Delta variant accounts for more than 80 percent of new U.S. COVID-19 cases, but the authorized vaccines remain more than 90 percent effective in preventing hospitalizations and deaths, said top U.S. infectious disease expert Anthony Fauci during a U.S. Senate hearing on Tuesday. 

Deaths from COVID-19 in the U.S. have averaged 239 per day over the past week, nearly 48 percent higher than the previous week, U.S. Centers for Disease Control and Prevention (CDC) Director Rochelle Walensky said during the hearing. 

The pace of vaccinations in the United States has dropped sharply in the past few months. Twelve states have yet to vaccinate 40 percent of their population, according to the data from CDC.

About 48.6 percent of the U.S. population is fully vaccinated against COVID-19, and 56.1 percent of the population has received at least one shot as of Monday, CDC data showed.

(With input from Xinhua and Reuters)