WASHINGTON — White House press secretary Jennifer Psaki said Tuesday that she is positive again for Covid and will not accompany President Biden to Europe this week for urgent meetings with world counterparts on Russia’s invasion of Ukraine.

Mr. Biden tested negative on Tuesday, she said.

Ms. Psaki’s reinfection is the latest Covid scare for the White House after recent positive tests for Vice President 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 Mr. Biden and other officials.

The scares come as the Biden administration is trying to help the United States ease back into its pre-pandemic norms, even as cases climb in Europe due to a new variant of the omicron variant of the coronavirus.

Ms. 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 Mr. Biden on Monday and that he is not considered a “close contact” under guidelines from the Centers for Disease Control and Prevention.

Ms. 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 Jacob Sullivan, who was joining her to discuss the trip.

After a brief delay, White House deputy press secretary Christopher Meagher entered and introduced Mr. Sullivan to a waiting White House press corps. Mr. Meagher read a statement on the changes caused by Ms. Psaki’s condition and on Judge Ketanji Brown Jackson’s appearance before the Senate Judiciary Committee for her Supreme Court confirmation hearing. He took no questions, while Mr. Sullivan delivered a statement and answered questions about Mr. Biden’s trip.

Ms. Psaki said she will follow CDC guidance and no longer accompany Mr. Biden to Belgium, where he will participate in a series of meetings with European and other world leaders on Russia’s war in Ukraine, and to Poland, which shares a border with Ukraine and has taken in millions of Ukrainians fleeing warfare.

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

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.

Douglas Emhoff, the vice president’s husband, tested positive on March 15, the White House announced. Ms. Harris, meanwhile, has continued to test negative.

The following day, the Irish prime minister, Micheál Martin, learned he had tested positive for Covid while attending a dinner event with American leaders, including Mr. Biden and Speaker Pelosi. Mr. Martin was due at the White House on March 17, to help celebrate St. Patrick’s Day with Mr. Biden, but he made those appearances on video instead because of his diagnosis.

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