To determine the rankings, which have been published in a map, researchers at The University of Texas at Austin and Johns Hopkins University analyzed counties across the country to find those with the lowest vaccination rates combined with the highest rates of international travel.
“We have long known that vaccine avoidance is a critical public health issue in the U.S. and Europe,” the study’s lead author Sahotra Sarkar explained in a statement, adding that “our results show how travel from regions elsewhere compounds this risk.”
Cook County, Ill. was named the most at-risk for a measles outbreak. It’s followed by Los Angeles County, Calif.; Miami-Dade County, Fla.; Queens, N.Y.; and King County, Wash.
The researchers identified counties in Washington, Oregon, California, and New York in the top 25 rankings that have already experienced some of the worst measles outbreaks in the country. Additionally, 30 of the 45 counties that have reported cases of the infectious disease to the CDC (which announced on Monday that there are now over 800 confirmed cases in the U.S. across 23 states) made the list.
Other areas that have a high risk include those with international airports, like Salt Lake, Utah; Travis, Texas; and Honolulu. According to the study, travelers who visit India, China, Mexico, Japan, Ukraine, Philippines, and Thailand are the most likely to return with measles.
Experts warn that the issue of low vaccination rates isn’t just contained to measles, either. “Pertussis — whooping cough — is another disease making a comeback because of dropping vaccination rates, and we predict serious outbreaks in the U.S. in the near future,” Sarkar warned, urging lawmakers to use their data to inform public health policy surrounding vaccines.