Minnesota colleges are reporting large spikes in COVID-19 cases on their campuses at the start of the spring semester, indicating the omicron variant is surging through their highly vaccinated communities in a way previous strains of the virus did not.

Nearly 1 in 4 University of Minnesota students who tested for COVID-19 at the Twin Cities campus' clinic from Jan. 6-13 were positive, according to data published Friday showing 253 positive student and employee cases out of 1,093 tests taken. Most U students are back on campus Tuesday for the start of spring semester classes.

"Our goal is to safely maintain continuity and in-person instruction but we recognize that Omicron is surging," U President Joan Gabel said in a message to students last week.

The U is requiring students and employees at its five campuses to be vaccinated against COVID-19 and encouraging them to get the booster shot. As of Jan. 5, 94% of university employees had submitted proof that they are partially or fully vaccinated and about 96% of students had reported they are vaccinated, according to Gabel.

High vaccination rates largely shielded the U and other Minnesota college campuses from spikes in COVID-19 cases last fall, when the delta variant was circulating. The omicron variant is proving much more transmissive, however, as the U's recent case count is by far its highest weekly number since vaccines became available early last year.

Following new guidance from the Centers for Disease Control and Prevention, the U has shortened the isolation period for students who've tested positive to five days if they have no symptoms or are improving. The U is expanding its testing capacity, providing upgraded masks to students and employees, and allowing professors who cannot teach in person for up to five straight weekdays due to COVID-19 infection or exposure the option to temporarily shift their classes online.

On Friday, Gabel announced the U will also temporarily require guests attending indoor athletic contests, performances and other events with 200 or more attendees to show proof of vaccination or a negative COVID-19 test taken 72 hours prior.

Faculty in the U's American Association of University Professors chapter and members of a union representing university clerical workers issued a joint statement last week calling on the U to move all classes online for the first two weeks of the semester to reduce virus transmission.

"Students, staff, and faculty are eager to return to campus this spring, but the University must do its part to limit community spread during the coming few weeks," the statement said.

Classes are set to begin Tuesday with no widespread shift online. The U is not planning further precautions than those already announced, university spokesman Jake Ricker said Friday.

Among Minnesota's private colleges, St. Olaf and Carleton, both located in Northfield, each reported more than 100 new positive cases over the past two weeks, and the University of St. Thomas in St. Paul reported 131 cases from Jan. 1-7.

The Minnesota State system tallied 1,077 total positive cases across its 30 public community colleges and seven universities from Jan. 5-12, according to data published Friday. That includes 860 positive cases among students and 217 among employees.

The total is far and away the highest weekly count the Minnesota State system has reported throughout the pandemic. Spring classes at Minnesota State schools began Jan. 10.

Minnesota State is not requiring all its students to be vaccinated. Its colleges and universities are requiring vaccination only for students living in college-owned housing, participating in intercollegiate athletics or working internships or clinical jobs. System employees are subject to a vaccination requirement for all state workers.

Across Minnesota State's colleges and universities, 65% of students had received at least one dose of a COVID-19 vaccine as of Dec. 1, according to state immunization data the system obtained.

Vaccination rates at the individual schools ranged from 43% at Northland Community and Technical College's campuses in East Grand Forks and Thief River Falls to 79% at Metropolitan State University in St. Paul.

In a memo last week, Minnesota State Chancellor Devinder Malhotra urged system college and university presidents to find ways to reduce campus foot traffic early in the semester, such as phasing in on-campus activities to help limit large gatherings.

"As the spring semester begins, our colleges and universities are continuing to adapt and are following appropriate mitigation measures," Malhotra said in a statement. "As has been the case since the onset of the pandemic, our top priorities remain protecting the health and safety of our students, our faculty, and our staff."