Colleges across the U.S. are starting to require booster shots, extend mask mandates and in some cases revert to online classes as they brace for the new omicron variant.

More than 20 colleges have said they will require boosters, including Boston University and Notre Dame. Others are extending mask mandates into next year, including Penn State.

Still others are planning to start next term online to prevent outbreaks after the holidays. The new variant comes as a gut punch to schools that were hoping to relax safety measures this spring and take a step toward normalcy.