WASHINGTON — Doug Emhoff, the husband of Vice President Kamala Harris, tested positive for the coronavirus on Tuesday, according to a statement from the White House.

“My symptoms are mild and I’m grateful to be both vaccinated and boosted,” Mr. Emhoff wrote on Twitter, encouraging others to get vaccinated and boosted as well.

Mr. Emhoff’s positive result forced Ms. Harris to back out of an event at the White House with President Biden advocating equal pay, according to Sabrina Singh, a spokeswoman for Ms. Harris. The vice president tested negative for the virus on Tuesday, Ms. Singh said.

“Out of an abundance of caution, the vice president will not participate in tonight’s event,” Ms. Singh said.

Ms. Harris stood alongside Mr. Biden earlier Tuesday during a bill signing. She also was at the President’s Daily Brief in the Oval Office, according to her schedule. Mr. Biden last received a negative test result on Sunday.

The prospect of the coronavirus spreading among the inner circle of the White House comes as Mr. Biden prepares to travel to Europe next week for a pivotal NATO summit to discuss the Russian invasion of Ukraine. Ms. Harris returned this weekend from a trip of her own in Europe, where she met with the presidents of Poland and Romania.

The virus has already begun to spread anew in Congress: At least nine House Democrats announced in the past five days that they had tested positive for the coronavirus, with more than half of those cases emerging after lawmakers attended a party retreat last week in Philadelphia — an event Mr. Biden attended to deliver a speech.

But there has been little sign that the White House or Congress would reimpose the precautions meant to mitigate the spread of the coronavirus. The Centers for Disease Control and Prevention issued guidance last month that was expected to relax mask-wearing requirements for most Americans, and many leaders across the country have made the decision to drop pandemic-era restrictions.

On Tuesday, Mr. Emhoff visited members of AmeriCorps at the Marvin Gaye Greening Center in Washington for an event on community-based gardens. He shoveled dirt and observed produce while chatting with workers at the green space project.

A White House official said Mr. Emhoff started to experience mild symptoms on Tuesday afternoon. He took an antigen test that was negative, the official said, but he then took a PCR test that came back positive. It was not clear when Mr. Emhoff was last tested before Tuesday afternoon.