Sarah Palin recently dined indoors in New York City while unvaccinated.

Sarah Palin, who is not vaccinated against the coronavirus, dined indoors Saturday night at Elio’s, an Italian restaurant on the Upper East Side of Manhattan that regularly draws celebrities, despite New York City’s requirement that all indoor guests show proof of vaccination. She tested positive for the virus on Monday.

“We just made a mistake,” said Luca Guaitolini, a manager for the restaurant, who was not working Saturday night but confirmed Ms. Palin’s visit. He said that the restaurant checked vaccination cards for all first-time customers but not for regulars who come each week, and that Ms. Palin had dined with a longtime guest, whom he declined to name.

“She probably just walked in and strolled over” to the table, Mr. Guaitolini said. “We are trying to get to the bottom of this.”

Ms. Palin’s lawyers did not immediately respond to a request for comment. Mr. Guaitolini said that the restaurant was notifying customers that they had been exposed to the coronavirus, and that the staff would be tested this week.

Ms. Palin, the former Alaska governor who ran for vice president in 2008, had traveled to New York for the trial of her defamation lawsuit against The New York Times. The trial was set to begin this week, but because of her positive test result, it will now start on Feb. 3. According to the judge in the case, Ms. Palin’s lawyers reported that she had received three Covid tests, all of which came back positive, and that she had not been vaccinated.

Shawn McCreesh, a features writer for New York Magazine, tweeted Monday that he had spotted Ms. Palin at Elio’s while out to dinner on Saturday night. (“My mom thought she was Tina Fey,” he wrote in a follow-up tweet.)

Brian Schwartz, a political finance reporter at CNBC, tweeted that he had also recently dined at the restaurant, and that the staff there had not verified his vaccination status.

New York City recorded 8,914 new coronavirus cases on Sunday, according to a Times database, 19,634 fewer than the Sunday before. Hospitalizations, which lag cases, have risen 106 percent in the past two weeks.

In light of the highly contagious Omicron variant, some restaurants have imposed more stringent safety measures for workers than those required by the government, including keeping Covid tests on hand and strictly enforcing the wearing of masks. But at many of these restaurants, including at Elio’s, the sole requirement for diners is that they be vaccinated.

Elio’s, which opened in 1981 on Second Avenue at East 84th Street, is known for its famous clientele, which has included Tom Hanks, Joan Didion and Mick Jagger. An obituary for the restaurant’s founder Elio Guaitolini, who died in 2016, described the place as “an informal clubhouse for Manhattan’s social and media elite.”

His son, Mr. Guaitolini, said Ms. Palin “is a controversial person wherever she goes. I just hope she has a speedy convalescence.”