A challenge to the University of Massachusetts’ COVID-19 vaccine mandate may have a mootness problem, a federal appellate judge suggested during oral arguments Thursday.

Judge Bruce Selya, of the U.S. Court of Appeals for the First Circuit, questioned whether the challenge brought by students Hunter Harris and Cora Cluett against the university’s Boston and Lowell campuses is still a live dispute since Harris is now enrolled at a different college and Cluett is set to graduate this month.