Northwestern University researchers have discovered Chicago has a unique COVID-19 virus strain that appears to be directly linked from the early outbreak in China, the university said in a news release Thursday.

Another variant discovered in Chicago COVID-19 patients, which happens to be the predominant variant worldwide, and in the U.S. is centered in New York, generates more of the virus in the upper airways than the Chicago version.

“This is the first clear evidence that genetic differences in the viruses are associated with differences in the characteristics of the infections that they cause,” said Dr. Egon Ozer, an assistant professor in infectious diseases at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician.