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A quarantine order was issued Thursday for hundreds of students and staff at two Los Angeles universities that may have been exposed to measles and either have not been vaccinated or can’t verify that they have immunity.

Measles in the United States has climbed to its highest level in 25 years, closing in on 700 cases this year in a resurgence largely attributed to misinformation that is turning parents against vaccines. Roughly three-quarters of this year’s illnesses have been in New York state.

The University of California, Los Angeles, said that as of Wednesday there were 119 students and 8 faculty members under quarantine. Seventy-one students and 127 staff members are quarantined at California State University, Los Angeles after a possible measles exposure at a campus library, school officials said.

The numbers were expected to change as students and staff turn in immunization records or take blood tests to establish immunization.

A person with a confirmed measles case visited the library at Cal State L.A. on April 11. Because the library receives about 2,000 visitors a day, the number of those exposed was not immediately known.

Authorities issued a blanket quarantine order for all students, faculty and staff who’ve been to the library on that date and asked those who visited between 11 a.m. and 3 p.m. to notify university officials.

“The Department of Public Health has determined that there is no known current risk related to measles at the library at this time,” Cal State said in a statement.

UCLA said some people could remain in quarantines for up to 48 hours before they prove immunity. A few may need to remain in quarantine for up to seven days, officials said.

Such an order mandates that the exposed people stay home and notify authorities “if they develop symptoms of measles, and to avoid contact with others until the end of their quarantine period or until they provide evidence of immunity,” the Los Angeles County Department of Public Health said in a statement.

Quarantine for measles can last up to 21 days from the date of the most exposure to the virus, health officials said.

The orders come as a small outbreak of measles is occurring in Los Angeles County involving five confirmed cases linked to overseas travel. The state recorded 38 measles cases as of Thursday; there were 11 around the same time last year, said Dr. Karen Smith, director of the California Department of Public Health.

Up to 10 of those cases were in Los Angeles County and four of them were linked to an outbreak from one unvaccinated traveler, officials said.

The state typically sees fewer than two dozen cases a year, Smith said.

This year, California’s cases stretch across 11 counties and affect patients from 5 months old to 55.

More than 76% of patients were not vaccinated or didn’t receive the recommended two doses of vaccine, Smith said. Fourteen of those infected had traveled overseas to countries including Philippines, Thailand, India and Ukraine.

Measles in most people causes fever, runny nose, cough and a rash all over the body. However, a very small fraction of those infected can suffer complications such as pneumonia and a dangerous swelling of the brain.

The Centers for Disease Control and Prevention recommends the vaccine for everyone over a year old, except for people who had the disease as children. Those who have had measles are immune.

The vaccine, which became available in the 1960s, is considered safe and highly effective, and because of it, measles was declared all but eliminated in the U.S. in 2000.

“Both universities are assisting with the implementation of quarantine orders and determining how best to support students who must be quarantined and who live on campus,” the news release said.

Officials reminded residents that one person with a confirmed measles case can infect thousands others.