More than 1000 students and staff members at two Los Angeles universities have been quarantined on campus or sent home this week, to contain the spread of measles.
Measles cases have reached a 25-year high in the US.
By Friday afternoon, two days after Los Angeles County ordered the precautions, about 325 of those affected had been cleared to return after proving their immunity to the disease, through either medical records or tests, health officials said.
The action at the University of University of California, Los Angeles, and California State University, Los Angeles - which together have more than 65,000 students - reflected the seriousness with which public health officials are taking the nation's outbreak.
The number of measles cases in the US has climbed to nearly 700 this year, including five in Los Angeles County and 38 altogether in California.
The surge is blamed largely on parents not getting their children vaccinated because of misinformation about the supposed dangers.
Cal State-LA reported 875 students, staff, faculty and visitors were placed under quarantine after possibly being exposed to measles earlier this month. About 250 had been cleared by Friday after proving they are immune to the disease.
At UCLA, 129 students and faculty were quarantined. All but 46 had been cleared by Friday.
Those covered by the quarantine were singled out based on their possible exposure to either an infected UCLA student who had attended classes in two buildings on three days earlier this month, or a person with measles who visited a Cal State-LA library on April 11, officials said.
Given the amount of time a person can remain contagious, officials said the quarantine would end at UCLA on Tuesday and at Cal State-LA on Thursday.
Measles usually causes fever, runny nose and an all-over rash but in a small number of cases can lead to deadly complications such as pneumonia and swelling of the brain.
