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Cornell University reported 903 cases of Covid-19 among students between December 7-13, and a “very high percentage” of them are Omicron variant cases in fully vaccinated individuals, according to university officials.

The school’s Covid-19 dashboard was updated late Tuesday afternoon, accounting for the jump in case numbers reported.

“Virtually every case of the Omicron variant to date has been found in fully vaccinated students, a portion of whom had also received a booster shot,” said Vice President for University Relations Joel Malina in a statement.

As of result, the school has decided to shut down its Ithaca, New York, campus, where it has about 25,600 students. Cornell’s overall vaccination rate among students is 99%.

The university will move final exams for the semester online, cancel all activities and athletics and close the libraries, President Martha Pollack wrote in a letter to the student body posted Tuesday.

Malina said the measures being taken on campus are to “help students who have tested negative to return safely home for the winter break, and in an effort to limit the spread of the Omicron variant to vulnerable populations.”

“While I want to provide reassurance that, to date, we have not seen severe illness in any of our infected students, we do have a role to play in reducing the spread of the disease in the broader community,” Pollack said.

The school has a mandatory vaccination policy for students, with exemptions for religious or medical issues. All unvaccinated students and many vaccinated students are required to take part in surveillance testing. Mask wearing indoors is compulsory.

Employees must be vaccinated by January 18. Ninety-seven percent of people on campus are fully vaccinated, the university says on its website.

“Cornell is not requiring members of our community to receive a booster at this time; however, as breakthrough cases continue to occur, we encourage you to consider receiving a booster,” officials said.

Cornell’s last day of classes was December 7 and its final exam period is scheduled from December 11-18, according to its online academic calendar.

Correction: A previous version of this story gave an inaccurate number for the percentage of students vaccinated. It is 99%.

CNN’s Sarah Boxer and Steve Almasy contributed to his report.