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Almost two-thirds of the nearly 800 students, faculty and staff members who were quarantined following exposure to the measles virus at two Los Angeles universities have been cleared to resume normal activities.

The quarantine marked one of the most sweeping efforts by authorities to contain the nation’s measles outbreak, where cases have reached a 25-year high.

People at California State University, Los Angeles and the University of California, Los Angeles were cleared after providing proof of immunity.

At the Cal State campus, 435 students and employees were cleared by Monday afternoon, with 221 still under quarantine.

Officials said they may have been exposed to an infected student who visited a school library.

At UCLA, 27 people remained quarantined. People at that campus were in classes attended by an infected student.