Updated at 6:23 p.m. ET
Hundreds of students and faculty at two universities in Los Angeles have been asked to stay home unless they can prove that they've been vaccinated against measles.
The LA campuses of the University of California and California State University imposed the quarantine after they became aware of people infected with measles who had potentially exposed hundreds. At UCLA, a student exposed at least 500 people earlier this month; at Cal State, someone with measles went to a library and encountered hundreds.
California officials said Friday the two campuses have more than 650 students and staff under quarantine order.
UCLA was notified by the LA County Department of Public Health that one of its students had contracted measles. After identifying people the infected student might have come in contact with while contagious, the school asked them to provide proof of immunization. On Wednesday, 119 people who couldn't provide proof were quarantined.
Of those, dozens were able to prove immunity and were released from quarantine by Thursday afternoon. But 82 were still quarantined, and "a few may need to remain in quarantine for up to seven days," the school said in a statement.
"Considering the time that has elapsed since the last possible exposure to the individual with measles on April 9, the highest risk period for developing measles has already passed — and the period during which symptoms may appear is nearing the end," UCLA Chancellor Gene Block said.
Los Angeles County declared Monday that the county was facing a measles outbreak, with international travel leading to five confirmed measles cases, including students from UCLA and Cal State L.A. So far this year, 38 people have been infected with measles in California, state officials said, according to the Los Angeles Times.
As of Wednesday, the Centers for Disease Control and Prevention was reporting 695 cases of measles from 22 states — the highest it's been since measles was ostensibly "eliminated" from the country in 2000. There's been a 300% increase in the number of measles cases worldwide over the first three months of 2018, according to the World Health Organization. "That increase is part of a global trend seen over the past few years as other countries struggle with declining vaccination rates and may be exacerbating the situation here," the CDC said.