Two Minnesota private colleges — Carleton and St. Olaf — announced this week they will require their students and employees to receive a booster dose of the COVID-19 vaccine.

The two colleges in Northfield are the first higher-education institutions in the state to require boosters. Carleton will require all students and employees who are eligible for a booster to get one by Jan. 21, while St. Olaf has set a deadline of Feb. 1.

Campus leaders cited concerns about the new omicron variant of COVID-19 and waning vaccine efficacy.

"Our high vaccination rate has been a primary factor in keeping COVID-19 transmission low on campus this fall," St. Olaf's campus-reopening lead Enoch Blazis wrote in a message to the campus community. "But with the vaccines' effectiveness waning over time, and with new, more transmissible variants contributing to breakthrough cases, it's clear our community will need booster shots to prevent additional spread of the virus."

Most private colleges in the state are requiring their students and employees to be fully vaccinated this fall, as are the University of Minnesota's five campuses. The Minnesota State system is requiring employees at its 30 community colleges and seven universities to be vaccinated, but not students.

The University of Minnesota is sticking with its current requirement for all students, faculty and staff to be fully vaccinated, spokesman Jake Ricker said.

"We continue to encourage everyone to get fully vaccinated," Ricker said. "Our current requirements align with CDC guidance on full vaccination and we will continue to monitor that."

Minnesota's largest private college, the University of St. Thomas, also "has no plans to require a booster" as of now, spokeswoman Vineeta Sawkar said.

Macalester College in St. Paul is "certainly considering the [booster] requirement," spokesman Joe Linstroth said, but leaders have not yet decided. They are consulting with the Minnesota Department of Health and monitoring guidance from the CDC. The college is holding booster shot clinics on its campus.

Gustavus Adolphus College in St. Peter is not requiring boosters, though campus leaders are encouraging students and employees to get them, spokesman JJ Akin said. The college's health service has administered about 300 boosters, he added.

"In partnership with the Minnesota Department of Health, Gustavus is continually evaluating its COVID-19 safety procedures and may ultimately require boosters based on the risks presented by new variants and emerging research on the waning effectiveness of vaccines over time," Akin said.