The University of Notre Dame will move its undergraduate classes online for two weeks in an attempt to curtail a surge in coronavirus cases on campus after reopening earlier this month, the school announced Tuesday. “If these steps are not successful, we’ll have to send students home as we did last spring,” President Rev. John Jenkins said during a conference call announcing the new curriculum. “The virus is a formidable foe. For the past week, it has been winning.”

The decision to move in-person classes online comes after 80 students tested positive on Monday for COVID-19 out of 418—or 19 percent of students who were tested. The surge in cases has been linked to at least two off-campus parties at Notre Dame, which is now reporting about 140 total cases since the school began to track two weeks ago, Jenkins said. According to the university, nearly 12,000 students were tested before arriving on campus and only 33 tests came back positive. “Our contact tracing analysis indicates that most infections are coming from off-campus gatherings. Students infected at those gatherings passed it on to others who in turn passed the virus on to a further group, resulting in the positive cases we have seen,” Jenkins said.