WASHINGTON (AP) — White House press secretary Jen Psaki said Tuesday that she is positive again for COVID-19 and will not accompany President Joe Biden to Europe this week for urgent meetings with world counterparts on Russia's invasion of Ukraine.

Biden tested negative on Tuesday, she said.

Psaki's reinfection follows recent positive tests for Vice President Kamala Harris' husband and Ireland's prime minister, who was in the nation's capital last week for a series of in-person celebrations of St. Patrick's Day with Biden and other officials.

The scares happened as the Biden administration tries to help the United States ease back into its pre-pandemic patterns, even as cases climb in Europe due to a new, more contagious variant of the omicron strain of the coronavirus.

Psaki tweeted that she took a laboratory test for COVID-19 as part of her preparation for the trip, which gets underway on Wednesday, and was later notified of a positive result.

She said she had two “socially distanced meetings” with Biden on Monday and that he is not considered a “close contact” under Centers for Disease Control and Prevention guidelines.

Psaki tweeted and released a statement a short time before she was scheduled to step into the White House press room for her daily briefing, accompanied by National Security Adviser Jake Sullivan, who was joining her to discuss the trip.

After a brief delay, White House deputy press secretary Chris Meagher entered and introduced Sullivan to a waiting White House press corps.

“Obviously, we've had some last-minute adjustments to the briefing, which is why I'm up here today," Meagher said before he read a statement on Supreme Court nominee Ketanji Brown Jackson's performance at her confirmation hearing before the Senate Judiciary Committee. He took no questions.

Sullivan made a statement and spent about 16 minutes answering questions about the trip.

Psaki said she will follow CDC guidance and not accompany Biden to Brussels, where he will attend a series of meetings with European and other world leaders on Russia’s war in Ukraine. Biden also plans to visit Poland, which shares a border with Ukraine and has taken in more than 2 million Ukrainians fleeing warfare following Russia's Feb. 24 invasion.

Psaki said she has experienced only mild symptoms of COVID-19 and credited being vaccinated against the disease. Under White House COVID-19 protocols, she said she will work from home and return to work at the end of a five-day isolation period and a negative test.

It's not unheard of for someone who has had COVID-19 to become infected again. Reinfections became more likely after the super-contagious omicron variant emerged, even among the fully vaccinated, but those cases tend to be very mild.

As coronavirus cases plummeted around the United States this year, and states and localities dropped their mask-wearing requirements, the White House did as well. As of March 1, neither White House staff nor reporters were required to wear face masks inside the building.

But some scientists are beginning to worry that the omicron variant known as BA.2 could soon push up COVID-19 cases in the United States, after months of case declines and people taking off their masks and returning to indoor spaces.

Harris' husband Doug Emhoff tested positive on March 15, though he is not considered a close contact of the president. Harris has continued to test negative.

The following day, Irish Prime Minister Micheál Martin learned he had tested positive for COVID-19 while attending a gala with U.S. leaders, including Biden. Martin was due to appear with Biden at the White House on St. Patrick's Day but instead made those appearances on video.

This is the second time that COVID-19 has forced Psaki to bow out of accompanying Biden abroad. She sat out last fall's trip to Rome and Glasgow, Scotland, after learning at the last minute that she had tested positive.