Sophomore student Khoa Nguyen waits with other students to enter a classroom on the USC campus Monday, August 23, 2021 for the first day of in-person classes. USC and California State University campuses start in-person classes on Monday, serving as a test case for whether vaccine mandates, masking, regular testing and other protocols can minimize spread of the Delta variant even as thousands of students congregate in classes, dorms and social events.