CHICAGO — A third COVID-19 variant has been identified in Illinois and the strain is thought to be more contagious than other ones.

Northwestern University researchers have determined the P.1 variant, first identified in travelers from Brazil, was confirmed in a Chicago resident. Health officials said their household partner also had COVID-19 and they did not travel outside of Illinois.

Health officials believe this variant is more contagious and may affect antibodies.

“Evidence suggests that this variant can spread more easily than most currently circulating strains of COVID-19, and there is some evidence that some mutations in the P.1 variant may affect the ability of antibodies (from natural infection or vaccination) to recognize and neutralize the virus, but additional studies are needed,” health officials said.

The first COVID-19 variant to be reported in Illinois was the B.1.1.7 variant, which was first identified in the United Kingdom. As of Friday, there are 85 cases of the B.1.1.7 variant and two cases of the B.1.351 variant, in addition to the P.1 variant.

Dr. Egon Ozer and his Pathogen Genomics research team made the discovery during their study of test samples from Northwestern Memorial Hospital. He said this patient was tested within the last month.

“We happened to identify that this one in particular was one of these variants of concern. And in this case, the Chicago Department of Public Health confirmed the patient and members of their household had not traveled outside Illinois before getting sick,” Dr. Ozer said.

On Friday, 1,442 new cases of COVID-19 were reported with 33 additional deaths.

A total of doses of 3,780,305 vaccine have been delivered to providers in Illinois, including Chicago.