Travis County is one of 25 counties in the U.S. that is at highest risk for a measles outbreak, according to a study published in The Lancet Infectious Diseases.

Researchers from Johns Hopkins University and UT Austin ranked Travis County 22nd on the list, citing its high rates of nonmedical childhood vaccination exemptions and its high volume of international travel.

Two other Texas counties made the list, as well. Harris County ranked ninth and Tarrant County ranked 12th. So far in 2019, Harris County has reported four cases of measles. Statewide, there have been 15 reported cases of measles this year.

Along with Honolulu and and Salt Lake counties, Travis is one of the most at-risk areas near an international airport that has yet to report a measles case. The study's authors said travel from countries including India, China, Mexico, Japan, Ukraine, Philippines and Thailand appeared to pose the greatest measles risk.

The number of confirmed measles cases in the U.S. has nearly doubled since last year, with more than 700 cases since January 2019, and researchers warned the epidemic could worsen.

“For measles, most experts believe that there will be one to two deaths per 1,000 cases, most likely infants," said the study’s lead author, Sahotra Sarkar, a philosophy and integrative biology professor at UT Austin. "We are set to see over 1,000 cases in the U.S. in 2019. So, for the first time since the 1980s, we may expect infant deaths from measles in the U.S."

The researchers involved in the study said their risk analysis should be used in the study of other vaccine-preventable diseases, such as mumps, rubella and whooping cough.

"The vaccine avoidance problem is not limited to measles," Sarkar said.