"The best protection against measles is through immunization, and everyone should make sure they and their family members are up to date on their vaccines," Allison Arwady, the Chicago Department of Public Health's acting commissioner told the WSJ.
According to Newsweek, the same person is believed to be responsible for both the Austin and Chicago incidents, with Austin public health officials confirming Monday the patient represents the city's first documented case of the virus in 20 years.
"Measles is an acute, highly contagious viral disease. A small number of cases are capable of quickly producing epidemics," Dr. Mark Escott, interim health authority and medical director for Austin Public Health, said in a statement posted to the organization's website.
Another infected person reportedly visited Richmond's International Airport in Virginia on Dec. 17 as well as a local doctor's office a few days later, Newsweek reported.
The high alerts began, however, after health officials in Colorado and California determined three unvaccinated children traveled through both Los Angeles and Denver International airports Dec. 11, following a flight from New Zealand.
According to the WSJ, more than 1,200 confirmed measles cases have been reported year-to-date across the United States, giving 2019 the distinction of yielding the most confirmed cases nationwide since 1992.