The large volume of travelers arriving daily in Los Angeles County make it the second most vulnerable place in the nation to a measles outbreak, according to a study released Thursday.

The study, published in the journal Lancet Infectious Diseases, put the county second only to Cook County, Illinois.

In 2019, seven people with measles have passed through Los Angeles International Airport and one through Long Beach Airport.

San Diego and San Mateo counties also made the top 25 in most vulnerable places, the report said. San Francisco International Airport is located in San Mateo County.

“The places, in particular in California — and also Cook County, which is where Chicago O’Hare (Airport) is — are really high on the list mainly because of the sheer volume of travelers,” Johns Hopkins civil engineering associate professor Lauren Gardner, an author of the paper, told the Los Angeles Times.

“It’s not just the fact that there are big airports, but those airports have a lot of incoming routes from countries having ongoing measles outbreaks.”

Nine measles cases have been reported in Los Angeles County this year. Travelers who visited parts of Southeast Asia where measles outbreaks had occurred brought the disease to California, but those cases did not expand into a major outbreak because of high vaccination rates in the state, the Times said.

Rankings for the study were based on how vulnerable a county was to having a single case of measles reported.

Because of California’s limited number of people exempt from vaccines, the state is somewhat protected from an outbreak, but Los Angeles County remains vulnerable, Gardner said.

“You could have another little town with higher exemption rates, but they’re not as well-connected to the rest of the world and they’re actually going to be at lower risk than Los Angeles,” Gardner said.

Following Cook and Los Angeles counties on the list were Miami-Dade County in Florida, King County in Washington and Queens in New York, where John F. Kennedy and LaGuardia airports are located. According to the New York City health department, Queens and Brooklyn have reported 466 cases of measles — the largest measles outbreak in the country this year.

At least 112,000 people have been diagnosed with measles outside the United States, according to the World Health Organization.

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