CHICAGO (CBS) — A new study in the medical journal “The Lancet” ranks Cook County as the most vulnerable place in the country for a measles outbreak.

It’s partly because of O’Hare International Airport. It serves many destinations, including places where parents don’t vaccinate their children.

“This is not going away, and as the anti-vaxxers dig in their heels, it means the epidemic is here to stay,” said Dr. Robert Murphy, professor of medicine and biomedical engineering at Northwestern University. “Europe is a mess. It’s even worse than here. They’re talking about fining people who aren’t vaccinated and limiting their ability to go to public places. It’s going to get nasty.”

Murphy said the Centers for Disease Control and Prevention is recommending people get a booster shot if they were vaccinated in 1968 or 1969, when the vaccine was less effective.

Los Angeles County was ranked second in the study, followed by Miami-Dade in Florida.

The United States has already seen more than 760 cases of measles. That’s the most since the disease was declared eliminated two decades ago.

“The measles, mumps, and rubella (MMR) vaccine confers lifelong protection with only one or two doses and is the most effective way to protect your family,” said Judd Hultquist, assistant professor of infectious diseases at Northwestern.